Ankle arthroplasty systems and methods

Abstract

The ankle arthroplasty system (100) may include a talar prosthesis (102) and a tibial prosthesis (104), each having an articular surface (110, 120) and a bone-engaging surface (112, 122). Each bone-engaging surface may have an anterior-posterior curvature and a medial-lateral curvature with a convex shape. A burr (610, 800, 830, 860) with a rotatable cutting element (720, 820, 850, 880) may be used to create a prepared surface on the talus or tibia to receive the corresponding prosthesis. A cutting guide may be used to guide the movement of the burr, and the cutting guide may include a base and an arm movably coupled to the base. One of the base and the arm may include a guide surface, and the other may have a follower that slides along the guide surface to constrain movement of the bar so that the preparation surface has at least one concave curvature and one convex curvature.

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to surgical systems and methods, and more particularly, to implants and associated methods for ankle arthroplasty. [Background technology]

[0002] An arthroplasty procedure is a surgical procedure in which one or more articular surfaces of a joint are replaced with an artificial articular surface. Such procedures are becoming increasingly popular. In particular, ankle arthroplasty may be required due to trauma or degeneration of the natural articular surfaces of the tibia and talus.

[0003] For the success of ankle arthroplasty, it is important that the postoperative kinematic characteristics of the ankle mimic, as closely as possible, those of the natural ankle. Furthermore, it is desirable for the ankle implant to remain in the correct position during the subsequent function of the joint. It is also desirable for the ankle arthroplasty procedure to be quick and smooth with little room for error. Many existing ankle arthroplasty implants and methods are biomechanically inaccurate, take a long time to implant, or do not form an adequate attachment to the underlying bone. Summary of the Invention [Problem to be solved by the invention]

[0004] The various systems and methods of the present disclosure have been developed in response to the state of the art, and in particular to technical problems and needs not yet fully addressed by currently available ankle arthroplasty systems and methods. The systems and methods of the present disclosure may provide ankle implants and devices, including but not limited to talar and tibial prostheses and devices, that improve biomechanics, provide superior bone fixation, and / or simplify implantation. [Means for solving the problem]

[0005] According to some embodiments, an ankle arthroplasty system may be designed to replace a natural talar articular surface on the talus and a natural tibial articular surface on the tibia. The ankle arthroplasty system may include a talar prosthesis and a tibial prosthesis, each of which has an articular surface and a bone-engaging surface. At least one of the bone-engaging surfaces may have a first anterior-posterior curvature and a medial-lateral curvature with a convex shape.

[0006] The first anterior-posterior curve may extend along substantially the entire anterior-posterior length of the bone-engaging surface. The bone-engaging surface may also have a keel projecting from the first anterior-posterior curve and extending along the anterior-posterior direction. The keel may have a base portion secured or integral with the remainder of the selected portion and a penetration portion extending from the base portion to penetrate the talus preparation surface or the tibial preparation surface. The penetration portion may have a generally semicircular periphery.

[0007] The talar articular surface may have two convex talar curves extending in a medial-lateral direction and a concave talar curve extending in the medial-lateral direction between the two convex talar curves. The tibial articular surface may have two concave tibial curves extending in the medial-lateral direction and a convex tibial curve extending in the medial-lateral direction between the two concave tibial curves. The talar articular surface and the tibial articular surface may be further shaped such that, with the tibial joint prosthesis centered on the talar joint prosthesis, the two concave tibial curves are substantially flush with the two convex talar curves.

[0008] The bone-engaging surface having the first anterior-posterior curvature may be the talus-engaging surface, and the first anterior-posterior curvature may be a concave curvature. The talus-engaging surface may further include a second medial-lateral curvature having a convex shape and extending in the medial-lateral direction, and a central flare extending substantially linearly along the medial-lateral direction between the first and second medial-lateral curvatures. The talus-engaging surface may further include a keel projecting from the first anterior-posterior curvature and extending along the anterior-posterior direction.

[0009] The bone-engaging surface with the first anterior-posterior curvature may be the tibial engaging surface, and the first anterior-posterior curvature may be a convex curvature. The tibial engaging surface may further include a second medial-lateral curvature having a convex shape and extending in the medial-lateral direction, and a central flare extending substantially linearly along the medial-lateral direction between the first and second medial-lateral curvatures. The tibial engaging surface may further include a keel projecting from the first anterior-posterior curvature and extending along the anterior-posterior direction.

[0010] According to some embodiments, the talar joint prosthesis may have a talar articular surface shaped to replace the natural talar articular surface, and a talar engagement surface shaped to engage the talar preparation surface of the talus, the talar engagement surface may have a first anterior-posterior curvature having a concave shape and extending in the anterior-posterior direction, and a first medial-lateral curvature having a convex shape and extending in the medial-lateral direction.

[0011] The first anterior-posterior curve may extend along substantially the entire length of the talus engaging surface in the anterior-posterior direction. The talus engaging surface may further include a second medial-lateral curve having a convex shape and extending in the medial-lateral direction, and a central extension extending substantially linearly along the medial-lateral direction between the first medial-lateral curve and the second medial-lateral curve. The talus engaging surface may further include a keel projecting from the first anterior-posterior curve and extending along the anterior-posterior direction. The keel may have a base portion secured or integral with a remainder of the talus engaging surface, and a penetration portion extending from the base portion to penetrate the talus preparation surface. The penetration portion may have a generally semicircular periphery.

[0012] According to some embodiments, the tibial joint prosthesis may have a tibial articular surface shaped to replace the natural tibial articular surface, and a tibial engagement surface shaped to engage the tibial preparation surface of the tibia, the tibial engagement surface may have a first anterior-posterior curvature having a convex shape and extending in the anterior-posterior direction, and a first medial-lateral curvature having a convex shape and extending in the medial-lateral direction.

[0013] The first anterior-posterior curvature may extend along substantially the entire length of the tibial engagement surface in the anterior-posterior direction. The tibial engagement surface may further include a second medial-lateral curvature having a convex shape and extending in the medial-lateral direction, and a central flare extending substantially linearly along the medial-lateral direction between the first medial-lateral curvature and the second medial-lateral curvature. The tibial engagement surface may further include a keel projecting from the first anterior-posterior curvature and extending along the anterior-posterior direction. The keel may have a base portion secured or integral with a remainder of the tibial engagement surface, and a through portion extending from the base portion to through the tibial preparation surface. The through portion may have a generally semicircular periphery.

[0014] According to some embodiments, a system for preparing a bone for joint formation may include a bur with a rotatable cutting element having a shape extending along the length of the rotatable cutting element selected from the group consisting of a concave shape and a convex shape. The system may further include a cutting guide including a bone attachment interface securable to the bone, a bur attachment interface securable to the bur, and a guide mechanism configured to constrain relative movement between the bur attachment interface and the bone attachment interface to facilitate formation of a preparation surface on the bone by the bur. The preparation surface may have at least one concave curvature or one convex curvature.

[0015] The cutting guide may further include a base and a bar holder. The base may have the bone attachment interface and a bar holder interface. The bar holder may have the bar attachment interface and a base interface bondable to the bar holder interface.

[0016] The guide mechanism may permit movement of the burr mounting interface along a first direction perpendicular to the length of the rotatable cutting element. The guide mechanism may guide movement of the burr mounting interface along a straight line perpendicular to the length of the rotatable cutting element. The shape of the rotatable cutting element may be convex with a maximum radius perpendicular to the length such that the preparation surface has a cross-sectional shape including a first convex curvature with a first radius of curvature substantially equal to a maximum radius, a second convex curvature with a second radius of curvature substantially equal to the maximum radius, and a central expansion extending substantially in a straight line between the first convex curvature and the second convex curvature.

[0017] The guide mechanism may further permit movement of the burr mounting interface along a second direction parallel to the length of the rotatable cutting element. The guide mechanism may permit movement of the burr mounting interface along the second direction by permitting rotation of the burr mounting interface about an axis perpendicular to the rotatable cutting element. The shape of the rotatable cutting element may be a concave shape with a maximum radius perpendicular to the length such that the preparation surface has a cross-sectional shape with a first convex curvature with a first radius of curvature substantially equal to a maximum radius, a second convex curvature with a second radius of curvature substantially equal to the maximum radius, and a central widening extending substantially linearly between the first convex curvature and the second convex curvature. The cross-sectional shape may be swept along the convex curvature.

[0018] According to some embodiments, a method for preparing a bone for joint formation may include positioning a cutting guide adjacent to the bone, the cutting guide may include a bone attachment interface, a bur attachment interface, and a guide mechanism. The method may further include affixing the bone attachment interface to the bone and affixing a bur to the bur attachment interface. The bur may include a rotatable cutting element with a shape extending along a length of the rotatable cutting element selected from the group consisting of a concave shape and a convex shape. The method may further include guiding, with the guide mechanism, the movement of the bur relative to the bone to facilitate formation of a preparation surface on the bone by the bur. The preparation surface may have at least one concave curvature or one convex curvature.

[0019] The cutting guide may have a base and a bar holder interface with the bone attachment interface. The cutting guide may further have a bar holder with the bar attachment interface and a base interface. The method may further include coupling the base interface of the bar holder to the bar holder interface of the base.

[0020] Guiding movement of the burr relative to the bone may include permitting movement of the burr with the guide mechanism along a first direction perpendicular to the length of the rotatable cutting element. Guiding movement of the burr relative to the bone may further include guiding movement of the bur attachment interface with the guide mechanism along a line perpendicular to the length of the rotatable cutting element. The shape may be a convex shape with a maximum radius perpendicular to the length such that the preparation surface has a cross-sectional shape including a first convex curvature with a first radius of curvature substantially equal to a maximum radius, a second convex curvature with a second radius of curvature substantially equal to the maximum radius, and a central extension extending substantially in a straight line between the first convex curvature and the second convex curvature.

[0021] Guiding the movement of the burr relative to the bone may further include permitting movement of the burr attachment interface along a second direction parallel to the length of the rotatable cutting element. Guiding the movement of the burr relative to the bone may further include permitting rotation of the burr attachment interface about an axis perpendicular to the rotatable cutting element. The shape may be a concave shape with a maximum radius perpendicular to the length such that the preparation surface has a cross-sectional shape with a first convex curvature with a first radius of curvature substantially equal to a maximum radius, a second convex curvature with a second radius of curvature substantially equal to the maximum radius, and a central flare extending substantially linearly between the first convex curvature and the second convex curvature. The cross-sectional shape may be swept along the convex curvature.

[0022] According to some embodiments, a system for preparing a talus or tibia for ankle arthroplasty may include a first bur and a first cutting guide. The first bur may have a first rotatable cutting element having a first shape extending along a length of the first rotatable cutting element. The first shape may be selected from the group consisting of a concave shape and a convex shape. The first cutting guide may include a first bone attachment interface securable to the talus or the tibia, a first bar attachment interface securable to the first bar, and a first guide mechanism configured to constrain relative movement between the first bar attachment interface and the first bone attachment interface by permitting movement of the first bar attachment interface along a first direction perpendicular to a first length of the first rotatable cutting element to facilitate formation of a first preparation surface on the talus or the tibia by the first bur. The first preparation surface may have at least one concave curvature or one convex curvature.

[0023] The first bone attachment interface may be fixable to the talus such that the first preparation surface is on the talus. The first guide mechanism may further permit movement of the first bur attachment interface along a second direction parallel to the first length of the first rotatable cutting element by permitting rotation of the first bur attachment interface about an axis perpendicular to the first rotatable cutting element. The first shape may be a concave shape such that the first preparation surface has a cross-sectional shape swept along a convex curvature.

[0024] The system may further include a second burr including a second rotatable cutting element having a convex shape, and a second cutting guide. The second cutting guide may include a second bone attachment interface securable to the tibia, a second bur attachment interface securable to the second bur, and a second guide mechanism configured to constrain relative motion between the second bur attachment interface and the second bone attachment interface by permitting movement of the second bur attachment interface along a third direction perpendicular to a second length of the second rotatable cutting element to facilitate formation of a second preparation surface on the tibia by the second bur. The second preparation surface may have at least one concave curvature.

[0025] The first cutting guide may further include a first base having the first bone attachment interface, and a first bar holder. The first base may further include a first bar holder interface. The first bar holder may have the first bar attachment interface and a first base interface coupleable to the first bar holder interface. The second cutting guide may further include a second base and a second bar holder. The second base may have the second bone attachment interface and a second bar holder interface. The second bar holder may have the second bar attachment interface and a second base interface coupleable to the second bar holder interface. The system may further include a third base interface attachable to the first base, and a fourth base interface attachable to the second base to facilitate positioning of the second base relative to the first base.

[0026] According to some embodiments, a method for performing ankle arthroplasty may include exposing an anterior side of the ankle, affixing a first cutting guide to a first bone, the talus or the tibia, inserting a first cutting instrument into the ankle from an anterior approach, and using the first cutting guide to guide movement of the first cutting instrument relative to the first bone to cause the first cutting instrument to form a first preparation surface on the first bone. The first preparation surface may have a first anterior-posterior curvature extending in an anterior-posterior direction. The method may further include placing a first prosthesis on the first preparation surface. The first prosthesis may have a first articular surface shaped to replace a first natural articular surface of the first bone.

[0027] The first prosthesis may have a keel. The method may further include inserting a second cutting instrument into the ankle from an anterior approach and guiding movement of the second cutting instrument relative to the first bone with the first cutting guide to cause the second cutting instrument to form a slot in the first bone such that the slot is oriented in an anterior-posterior direction. Placing the first prosthesis on the first preparation surface may include inserting the keel into the slot.

[0028] The first bone may be the tibia. The first anterior-posterior curve may be a concave curve extending in an anterior-posterior direction. The first prosthesis may have a convex bone-engaging surface. Placing the first prosthesis on the first preparation surface may include inserting the convex bone-engaging surface into the concave curve.

[0029] The first bone may be the talus. The first anterior-posterior curve may be a convex curve extending in an anterior-posterior direction. The first prosthesis may have a concave bone-engaging surface. Placing the first prosthesis on the first preparation surface may include positioning the convex curve on the concave bone-engaging surface.

[0030] The method may further include exposing an anterior side of the ankle, affixing a second cutting guide to the tibia, and inserting the first or second cutting instrument into the ankle from an anterior approach. The method may further include guiding the movement of the first or second cutting instrument relative to the tibia with the second cutting guide to cause the first or second cutting instrument to form a second preparation surface on the tibia such that the second preparation surface has a second anterior-posterior curvature with a concave curvature extending in an anterior-posterior direction. The method may include placing a second prosthesis on the second preparation surface. The second prosthesis may have a convex bone-engaging surface and a second articular surface shaped to replace a second natural articular surface of the tibia. The step of placing the second prosthesis on the second preparation surface may include inserting the convex bone-engaging surface into the concave curvature.

[0031] The first cutting guide may have a talus base with a talus attachment interface and a talus instrument holder interface, and a talus instrument holder with a talus instrument attachment interface and a talus base interface. Securing the first cutting guide to the first bone may include securing the talus attachment interface to the talus. The method may further include coupling the talus base to the talus instrument holder by coupling the talus instrument holder interface to the talus base interface, and attaching the first cutting instrument to the talus instrument attachment interface prior to guiding movement of the first cutting instrument with the first cutting guide.

[0032] The method may further include positioning a trial on the talus prior to the step of securing the talar base to the talus. The trial may be coupled to a distal end of a post. The method may further include using the post to align the trial with the talus by aligning a proximal end of the post with a landmark on a portion of the patient's leg proximal to the talus, and aligning the trial with the talar base prior to the step of securing the talar base to the talus.

[0033] The method may further include attaching a talus base interface of an alignment block to the talus base and attaching a tibial base interface of the alignment block to a tibial base. The tibial base may have a tibial mounting interface and a tibial instrument holder interface. The method may further include affixing the tibial mounting interface to the tibia and coupling the tibial instrument holder to the tibial base by coupling the tibial instrument holder interface to the tibial base interface of the tibial instrument holder. The tibial base and the tibial instrument holder may comprise a second cutting guide.

[0034] The method may further include mounting the first or second cutting instrument to a tibial instrument mounting interface of the tibial instrument holder, inserting the first or second cutting instrument into the ankle joint from an anterior approach, and guiding, with the second cutting guide, movement of the first or second cutting instrument relative to the tibia in a medial-lateral direction to cause the first or second cutting instrument to form a second preparation surface on the tibia, the second preparation surface having a second anterior-posterior curvature with a concave curvature extending in an anterior-posterior direction.

[0035] Guiding movement of the first cutting instrument relative to the first bone to create the first preparation surface may include moving the first cutting instrument in a medial-lateral direction. Guiding movement of the first cutting instrument relative to the first bone to create the first preparation surface may further include rotating the first cutting instrument relative to the first bone about an axis extending in a medial-lateral direction to move the first cutting instrument in an anterior-posterior direction.

[0036] According to some embodiments, a method for performing ankle arthroplasty on an ankle joint including a talus and a tibia may include exposing an anterior side of the ankle joint, affixing a talus cutting guide to the talus, and inserting a first cutting instrument into the ankle joint from an anterior approach. The method may further include guiding a motion of the first cutting instrument relative to the talus with the talus cutting guide to rotate the first cutting instrument relative to the talus about an axis extending in a medial-lateral direction to move the first cutting instrument in an anterior-posterior direction to form a first preparation surface on the talus. The first preparation surface may have a first anterior-posterior curvature extending in an anterior-posterior direction. The method may further include placing a talar prosthesis on the first preparation surface. The talar prosthesis may have a talar articular surface shaped to replace a natural talar articular surface of the talus.

[0037] The talar prosthesis may have a keel. The method may further include inserting the first or second cutting instrument into the ankle from an anterior approach and using the talar cutting guide to guide movement of the first or second cutting instrument relative to the talus to cause the first or second cutting instrument to form a slot in the talus such that the slot is oriented in an anterior-posterior direction. Placing the talar prosthesis on the first preparation surface may include inserting the keel into the slot.

[0038] The step of guiding the movement of the first cutting instrument relative to the talus to create the first preparation surface may further include moving the first cutting instrument in a medial-lateral direction. The method may further include the steps of affixing a tibial cutting guide to the tibia and inserting the first or second cutting instrument into the ankle joint from an anterior approach. The method may further include guiding the movement of the first cutting instrument relative to the tibia with the tibial cutting guide to move the first or second cutting instrument in a medial-lateral direction to create a second preparation surface on the tibia. The second preparation surface may have a second anterior-posterior curve extending in an anterior-posterior direction. The method may further include mounting a tibial prosthesis on the second preparation surface. The tibial prosthesis may have a tibial articular surface shaped to replace a natural tibial articular surface of the tibia.

[0039] The talus cutting guide may have a talus base and a talus instrument holder. The talus base may have a talus attachment interface and a talus instrument holder interface. The talus instrument holder may have a talus instrument attachment interface and a talus base interface. Securing the talus cutting guide to the talus may include securing the talus attachment interface to the talus. The method may further include coupling the talus base to the talus instrument holder by coupling the talus instrument holder interface to the talus base interface and attaching the first cutting instrument to the talus instrument attachment interface prior to guiding movement of the first cutting instrument with the talus cutting guide.

[0040] The method may further include attaching a talus base interface of an alignment block to the talus base and attaching a tibial base interface of the alignment block to a tibial base. The tibial base may have a tibial mounting interface and a tibial instrument holder interface. The method may further include fixing the tibial mounting interface to the tibia and coupling the tibial instrument holder to the tibial base by coupling the tibial instrument holder interface to the tibial base interface of the tibial instrument holder. The tibial base and the tibial instrument holder may comprise a second cutting guide.

[0041] According to some embodiments, a method for performing ankle arthroplasty on an ankle joint including a talus and a tibia may include exposing an anterior side of the ankle joint, securing a talus cutting guide to the talus, inserting a first cutting instrument into the ankle joint along an anterior approach, and guiding movement of the first cutting instrument relative to the talus with the talus cutting guide to cause the first cutting instrument to form a first preparation surface on the talus. The first preparation surface may have a first anterior-posterior curvature extending in an anterior-posterior direction. The method may further include securing a tibial cutting guide to the tibia, inserting the first cutting instrument or a second cutting instrument into the ankle joint along the anterior approach, and guiding movement of the first cutting instrument or the second cutting instrument relative to the tibia with the tibial cutting guide to cause the first cutting instrument or the second cutting instrument to form a second preparation surface on the tibia. The second prepared surface may have a second anterior-posterior curvature extending in an anterior-posterior direction. The method may further include mounting a talar prosthesis on the first prepared surface and mounting a tibial prosthesis on the second prepared surface. The talar prosthesis may have a talar articular surface shaped to replace a first natural articular surface of the talus, and the tibial prosthesis may have a tibial articular surface shaped to replace a second natural articular surface of the tibia.

[0042] The talar prosthesis may include a talar keel and the tibial prosthesis may include a tibial keel. The method further includes guiding, with the talar cutting guide, the movement of the first cutting instrument, the second cutting instrument, or the third cutting instrument relative to the talus to form a first slot in the talus such that the first slot is oriented in an anterior-posterior direction. The method further includes guiding, with the tibial cutting guide, the movement of the first cutting instrument, the second cutting instrument, the third cutting instrument, or the fourth cutting instrument relative to the tibia to form a second slot in the tibia such that the second slot is oriented in an anterior-posterior direction. The step of placing the talar prosthesis on the first preparation surface may include the step of inserting the talar keel into the first slot. The step of placing the tibial prosthesis on the second preparation surface may include the step of inserting the tibial keel into the second slot.

[0043] The talus cutting guide may have a talus base and a talus instrument holder. The tibial cutting guide may have a tibial base and a tibial instrument holder. Securing the talus cutting guide to the talus may include securing the talus base to the talus. The method may further include attaching a talus base interface of an alignment block to the talus base and attaching a tibial base interface of the alignment block to the tibial base prior to guiding the movement of the first cutting instrument or the second cutting instrument with the tibial cutting guide. Securing the tibial cutting guide to the tibia may include securing the tibial base to the tibia with the talus base interface attached to the talus base and the tibial base interface attached to the tibial base.

[0044] According to some embodiments, a system for preparing a bone for joint formation may include a cutting instrument and a guide assembly securable to the bone. The guide assembly may have a base and an arm. The base may have a first mating feature and a first guide feature. The arm may have a second mating feature movably coupled to the first mating feature, an instrument mounting interface mountable to the cutting instrument, and a second guide feature. One of the first guide feature and the second guide feature may have a guide surface having a predetermined shape. The other of the first guide feature and the second guide feature may include a follower configured to slide along the guide surface to constrain movement of the instrument mounting interface relative to the base.

[0045] The first and second coupling features may be coupled to one another to allow the arm to rotate relative to the base about an arm rotation axis. The guide surface may face either toward or away from the arm rotation axis. The guide surface may have a planar shape configured to prevent movement of a cutting instrument axis of the cutting instrument beyond a planar boundary to prevent over-penetration of the bone by the cutting instrument. The cutting instrument may include a burr with a cutting element that rotates about the cutting instrument axis.

[0046] The guide surface may be on the base and the follower may be on the arm. The follower may include a cylindrical post that protrudes from a remainder of the arm.

[0047] The arm may include a first arm member having at least a portion of the second coupling feature, and a second arm member slidably coupled to the first arm member having the instrument mounting interface and the second guide feature. The system may further include a resilient member urging the follower toward the guide surface and urging the cutting instrument toward the bone.

[0048] The guide assembly may further include a base having a bone mounting interface mountable to the bone and a base mounting interface mountable to a base mounting interface of the base. The base may further include a stationary member having the bone mounting interface, and a movable member coupled to the stationary member for rotation relative to the stationary member about a base axis perpendicular to the arm rotation axis. The movable member may have the base mounting interface.

[0049] The bone may be a talus or a tibia. The bone attachment interface may be configured to attach the base to the talus or the tibia proximate an ankle joint defined by the talus or the tibia.

[0050] According to some embodiments, a method for preparing a bone for joint formation may include affixing a guide assembly to a bone. The guide assembly may include a base and an arm. The base may include a first mating feature and a first guide feature. The arm may include a second mating feature movably coupled to the first mating feature, an instrument mounting interface, and a second guide feature. The method may further include mounting a cutting instrument to the instrument mounting interface, and moving the arm relative to the base to guide movement of the cutting instrument relative to the bone to cause the cutting instrument to form a preparation surface on the bone. One of the first guide feature and the second guide feature may include a guide surface with a predetermined shape. The other of the first guide feature and the second guide feature may include a follower. Moving the arm relative to the base may include sliding the follower along the guide surface to constrain movement of the instrument mounting interface relative to the base.

[0051] Moving the arm relative to the base may further include rotating the arm relative to the base about an arm rotation axis, and the guide surface may face either towards or away from the arm rotation axis.

[0052] The guide surface may have a planar shape. The cutting instrument may include a bur with a cutting element that rotates about a cutting instrument axis. Sliding the follower along the guide surface to constrain movement of the instrument mounting interface relative to the base may include preventing movement of the cutting instrument axis beyond a planar boundary to prevent over-penetration of the bone by the bur.

[0053] The arm may include a first arm member having at least a portion of the second coupling feature, and a second arm member slidably coupled to the first arm member having the instrument mounting interface and the second guide feature. Sliding the follower along the guide surface to constrain movement of the instrument mounting interface relative to the base may include sliding the second arm member relative to the first arm member. The guide assembly further includes a resilient member. Sliding the follower along the guide surface to constrain movement of the instrument mounting interface relative to the base may include urging the follower toward the guide surface with the resilient member and urging the cutting instrument toward the bone.

[0054] The guide assembly may further include a base comprising a stationary member having a bone mounting interface and a movable member rotatably coupled to the stationary member. The movable member may have a base mounting interface. Securing the guide assembly to the bone may include mounting the bone mounting interface to a talus. The method may further include mounting a base mounting interface of the base to the base mounting interface prior to moving the arm relative to the base to guide movement of the cutting instrument relative to the bone. Moving the arm relative to the base to guide movement of the cutting instrument relative to the bone may include rotating the movable member relative to the stationary member about a base axis.

[0055] The guide assembly may further have a base with a bone mounting interface and a base mounting interface. Securing the guide assembly to the bone may include mounting the bone mounting interface to a tibia. The method may further include mounting a base mounting interface of the base to the base mounting interface prior to moving the arm relative to the base to guide movement of the cutting instrument relative to the bone.

[0056] According to some embodiments, a system for preparing a talus or tibia for ankle arthroplasty may include a bar with a cutting element that rotates about a bar axis, and a guide assembly that is securable to the talus or tibia. The guide assembly may have a first coupling feature, a base with a first guide feature, and an arm. The arm may have a first arm member with at least a portion of a second coupling feature coupled to the first coupling feature as an arm that allows the arm to rotate relative to the base about an arm rotation axis. The arm may also have a second arm member slidably coupled to the first arm member. The second arm member may have an instrument mounting interface, a second guide feature, and a resilient member that is attachable to the bar. One of the first guide feature and the second guide feature may include a guide surface having a planar shape configured to prevent movement of the bar axis beyond a planar boundary to prevent over-penetration of the talus or tibia by the bar. The other of the first and second guide features may include a follower configured to slide along the guide surface to constrain movement of the instrument mounting interface relative to the base, and the resilient member may urge the follower toward the guide surface and urge the bur toward the talus or the tibia.

[0057] These and other features of the present disclosure will become more fully apparent from the following description and appended claims, or may be learned by the practice of the systems and methods described below. [Brief description of the drawings]

[0058] Exemplary embodiments of the present disclosure will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings, in which: Exemplary embodiments of the present disclosure will be described with additional specificity and detail through the use of the accompanying drawings, with the understanding that these drawings merely depict exemplary embodiments and therefore should not be considered limiting of the scope of the appended claims. [Figure 1] FIG. 1 is a perspective view of an ankle arthroplasty system according to one embodiment. [Figure 2A] FIG. 2 is a cranial perspective view of a talar prosthesis. [Figure 2B] FIG. 2 is a caudal perspective view of the talar prosthesis. [Figure 2C] FIG. 2 is a side view of a talar prosthesis. [Figure 2D] FIG. 2 is a lateral cross-sectional view of a talar prosthesis. [Figure 2E] FIG. 2 is an anterior cross-sectional view of a talar prosthesis. [Figure 3A] FIG. 2 is a cranial perspective view of a tibial prosthesis. [Figure 3B] FIG. 2 is a caudal perspective view of the tibial prosthesis. [Figure 3C] FIG. 2 is a side view of a tibial prosthesis. [Figure 3D] FIG. 2 is a lateral cross-sectional view of a tibial prosthesis. [Figure 3E] FIG. 2 is an anterior cross-sectional view of a tibial prosthesis. [Figure 4A] FIG. 13 is a cranial perspective view of a trial that may be used to position the talar base relative to the talus through the use of a post. [Figure 4B] FIG. 13 is a caudal perspective view of a trial that may be used to position the talar base relative to the talus through the use of a post. [Figure 4C] FIG. 4C is a cranial perspective view of a trial that may be used to position a talar base relative to the talus through the use of a post, with the talar base and post assembled with the talus and trial. [Figure 5A] FIG. 4D is a posterotemporal perspective view of the talar base of FIG. 4C. [Figure 5B] FIG. 4D is an anterior-temporal perspective view of the talar base of FIG. 4C. [Figure 5C] 5C is an anterior-temporal perspective view of the talar base of FIG. 4C, where the talar base is secured to the talus. [Figure 6A] FIG. 13 is a front perspective view of a talus bar holder secured to the talus base to hold a bar against the talus. [Figure 6B] FIG. 13 is a posterior perspective view of a talus bar holder secured to the talar base to hold a bar against the talus. [Figure 7A] FIG. 6C is a perspective view of the bar of FIGS. 6A and 6B. [Figure 7B] FIG. 6C is a side view of the bar of FIGS. 6A and 6B. [Figure 7C] FIG. 6C is a cross-sectional plan view of the bar of FIGS. 6A and 6B. [Figure 8A] FIG. 1 is a side view of a bar according to various embodiments. [Figure 8B] FIG. 1 is a side view of a bar according to various embodiments. [Figure 8C] FIG. 1 is a side view of a bar according to various embodiments. [Figure 9A] FIG. 6C is a cranial perspective view of the talar bar holder of FIGS. 6A and 6B. [Figure 9B] FIG. 6C is a caudal perspective view of the talar bar holder of FIGS. 6A and 6B. [Figure 9C] FIG. 6C is a front cross-sectional view of the talar bar holder of FIGS. 6A and 6B. [Figure 10A] FIG. 1 is an anterior perspective view of the talus with the talar base attached to the talus, the talar bar holder attached to the talar base, and the bar positioned to resect the anterior portion of the natural articular surface of the talus. [Figure 10B] FIG. 2 is a posterior perspective view of the talus with the talar base attached to the talus, the talar bar holder attached to the talar base, and the bar positioned to resect the anterior portion of the natural articular surface of the talus. [Figure 11A]10C is a cross-sectional view of the lateral surface of the talus with the talar base, the talar bar holder, and the bar positioned as in FIGS. 10A and 10B. FIG. [Figure 11B] FIG. 1C is an enlarged cranial lateral view of the talus with the talar base, the talar bar holder, and the bar positioned as in FIGS. 10A and 10B. [Figure 12] FIG. 13 is a perspective view depicting the formation of a slot in the preparation surface of the talus using the burr. [Figure 13A] FIG. 1 is a posterior caudal perspective view of the tibial base. [Figure 13B] FIG. 1 is an anterior view of the tibial base. [Figure 13C] FIG. 13C is an anterior-temporal perspective view of the tibial base, with an alignment block and talar base also depicted in FIG. 13C for securing the tibial base to the tibia. [Figure 14A] FIG. 13 is an anterior temporal perspective view of the tibial bar holder. [Figure 14B] FIG. 13 is a side view of the tibial bar holder. [Figure 14C] FIG. 14C is an anterior-temporal perspective view of a tibial bar holder secured to the tibial base and the tibia. [Figure 15] 13 is a cross-sectional view of the lateral surface of the tibial bar holder and the tibial base secured to the tibia. [Figure 16] A cross-sectional view of a lateral surface depicting the talus and the tibia with the talar prosthesis secured to the prepared surface of the talus and the tibial prosthesis secured to the prepared surface of the tibia. [Figure 17A] FIG. 4B is a perspective view of a talus with a portion of the trial of FIGS. 4A-4C placed on the concave curvature of the talus, along with a talar base according to an alternative embodiment. [Figure 17B] 17B is a perspective view of the talus base of FIG. 17A, the talus base 1710 being secured to the talus 420. FIG. [Figure 18A] FIG. 17C is a perspective view of the talar base of FIGS. 17A and 17B with a talar bar holder secured to a movable member of the talar base; [Figure 18B] FIG. 17C is a perspective view of the talar base of FIGS. 17A and 17B with a talar bar holder secured to a movable member of the talar base; [Figure 19] FIG. 17C is a side cross-sectional view of the talar base of FIGS. 17A and 17B with a talar bar holder secured to the movable member of the talar base; [Figure 20A] FIG. 13 is an exploded perspective view of an alignment block according to an alternative embodiment. [Figure 20B] FIG. 13 is a rear view of an alignment block according to an alternative embodiment. [Figure 20C] FIG. 13 is a front view of an alignment block according to an alternative embodiment. [Figure 20D] FIG. 13 is a side view of an alignment block according to an alternative embodiment. [Figure 20E] FIG. 13 is a side exploded view of an alignment block according to an alternative embodiment. [Figure 21A] FIG. 17C is a perspective view of the talar base of FIGS. 17A and 17B attached to the talus and tibial base positioned relative to the tibia through the use of the alignment block and tibial trial. [Figure 21B] FIG. 17C is a side view of the talar base of FIGS. 17A and 17B attached to the talus and tibial base being positioned relative to the tibia through the use of the alignment block and tibial trial. [Figure 22A] FIG. 17C is a front view of the talar base of FIGS. 17A and 17B attached to the talus and tibial base being positioned relative to the tibia through the use of the alignment block and tibial trial. [Figure 22B] FIG. 17C is a perspective view of the talar base of FIGS. 17A and 17B attached to the talus and tibial base positioned relative to the tibia through the use of the alignment block and tibial trial. [Figure 22C] FIG. 17C is a side cross-sectional view of the talar base of FIGS. 17A and 17B attached to the talus and tibial base being positioned relative to the tibia through the use of the alignment block and tibial trial. [Diagram 23]FIG. 17C is a perspective view of a tibial bar holder secured to the tibial base of FIGS. 17A and 17B to hold a bar against the tibia. [Figure 24A] FIG. 13 is a top view of a patient-specific mounting plate that may be used as part of a patient-specific guide mechanism for the talus, according to one embodiment. [Figure 24B] FIG. 13 is a bottom view of a patient-specific mounting plate that may be used as part of a patient-specific guide mechanism for the talus, according to one embodiment. [Figure 24C] FIG. 13 is a side view of a patient-specific mounting plate that may be used as part of a patient-specific guide mechanism for the talus, according to one embodiment. [Figure 25A] FIG. 25 is a perspective view of the patient-specific mounting plate of FIGS. 24A to 24C on the talus. [Figure 25B] FIG. 24B is a perspective view of the patient-specific mounting plate and talus of FIG. 24A, with a non-moving component secured to the patient-specific mounting plate to define a non-moving member functionally similar to the non-moving member of FIGS. 5A and 5B and the non-moving member of FIGS. 17A and 17B. [Figure 26A] 25A and 25B, where the talar bar holder is secured to the movable member defined by the patient-specific mounting plate and the stationary component of FIGS. 24A to 25B. [Figure 26B] FIG. 25C is a side view of the talar base of FIGS. 25A and 25B, in which the talar bar holder is secured to the movable member defined by the patient-specific mounting plate and the stationary component of FIGS. 24A to 25B. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0059] Exemplary embodiments of the present disclosure will be best understood with reference to the drawings, in which like parts are designated with like numerals throughout. It will be readily understood that the components of the present disclosure, as generally described herein and illustrated in the drawings, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the present embodiments of the present devices, systems, and methods, as represented in Figures 1 through 16, are not intended to limit the scope of the claims, but are merely illustrative examples of example embodiments.

[0060] The terms "connected," "coupled," and "in communication with" refer to any form of interaction between two or more things, including mechanical, electrical, magnetic, electromagnetic, fluid, and thermal interaction. Two components can be operatively coupled to one another even if they are not in direct contact with one another. The term "in contact" refers to items that are in direct physical contact with one another, but the items are not necessarily attached to one another.

[0061] The word "exemplary" is used herein to mean serving as an example, instance, or illustration. Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. Various aspects of the present embodiments are presented in drawings, which are not necessarily drawn to scale unless specifically indicated.

[0062] 1A, 1B, and 1C are perspective, side, and anterior cross-sectional views, respectively, of an ankle arthroplasty system, or system 100, according to one embodiment. System 100 may be designed to replace the natural articular surfaces of the ankle joint and thus may include a talar prosthesis 102 and a tibial prosthesis 104. In some embodiments, the system 100 may be designed to replace only the articular surfaces of the talus or tibia and thus may include only the talar prosthesis 102 or the tibial prosthesis 104.

[0063] The talar prosthesis 102 and tibial prosthesis 104 may each have an articular surface and a bone-engaging surface. Specifically, the talar prosthesis 102 may have a talar articular surface 110 shaped to replace the natural articular surface of the talus, and a talar engaging surface 112 shaped to engage a talar preparation surface of the talus, either by direct contact if the talar engaging surface 112 is a porous in-growth material, or through a layer of adhesive such as polymethacrylate (PMMA, i.e., "bone cement"). Similarly, the tibial prosthesis 104 may have a tibial articular surface 120 shaped to replace the natural articular surface of the tibia, and a tibial engaging surface 122 shaped to engage with a tibial preparation surface of the tibia, either by direct contact if the tibial engaging surface 122 is a porous ingrowth material, or through a layer of adhesive such as PMMA.

[0064] The system 100 is shown with respect to directions applicable when the system 100 is implanted in an ankle joint. These directions may include an anterior-posterior direction 130, a medial-lateral direction 132, and a cranio-caudal direction 134. In this application, these directions may be referred to, for example, as "in the anterior-posterior direction 130" or "in the anterior-posterior direction." Direction may refer to the motion of an object, e.g., an object moving in the anterior-posterior direction 130 moves in the anterior direction and / or the posterior direction. Alternatively, direction may refer to the orientation of an object or feature. For example, an object or feature extending in the anterior-posterior direction is oriented such that the object's or feature's longest length is generally parallel to the anterior-posterior direction 130.

[0065] The talar prosthesis 102 is shown and described in more detail in connection with Figures 2A-2E, and the tibial prosthesis 104 is shown and described in more detail in connection with Figures 3A-3E.

[0066] 2A-2E are cranial perspective, caudal perspective, lateral, lateral, and anterior sectional views of the talar prosthesis 102, respectively. The talar articular surface 110 may be shaped to mimic the shape of the natural talar articular surface. In some embodiments, the talar articular surface 110 may have two convex talar curves 200 extending in a medial-lateral direction. The convex talar curves 200 may be separated from each other by a concave talar curve 202 extending in a medial-lateral direction. The convex talar curves 200 and the concave talar curves 202 are best seen in FIG. 2E, where the cut plane extends in a medial-lateral and cranio-caudal direction, i.e., parallel to the convex talar curves 200 and the concave talar curves 202.

[0067] The talus engaging surface 112 may be shaped to provide secure engagement with a prepared surface of the talus as shown and described below, using either a porous bone ingrowth surface or a surface adapted for bone cement. In some embodiments, the talus engaging surface 112 may have a main portion 210 and a keel 212 extending from the main portion 210. The main portion 210 may have a contour that helps the main portion 210 remain securely seated on the talus while leaving much of the adjacent bone of the talus intact. Thus, the talus prosthesis 102 may be a "bone sparing" prosthesis.

[0068] In some embodiments, the main portion 210 may have two medial-lateral curved portions 220 located at the edge of the talus engaging surface 112, and a central extension 222 extending substantially straight in the medial-lateral direction between the two medial-lateral curved portions 220. The medial-lateral curved portions 220 and the central extension 222 are best seen in FIG. 2E, where a cut plane extends in the medial-lateral and cranio-caudal directions, i.e., parallel to the medial-lateral curved portions 220 and the central extension 222. The central extension 222 may optionally be slightly recessed relative to the medial-lateral curved portions 220 to define a wall 224 facing toward the keel 212. The wall 224 may be arranged in a circumferential manner and may act as a retaining wall for the bone cement when the talus prosthesis 102 is implanted. If the talar prosthesis 102 is to be secured to the bone using a porous interface, the wall 224 may be used to contain the porous material.

[0069] The main portion 210 may also have an anterior-posterior curvature 230 extending in the anterior-posterior direction. Thus, the cross-sectional shape of the main portion 210 may be generally arcuate with a concave shape when viewed from a lateral perspective, as in FIG. 2C, and generally rectilinear when viewed from an anterior perspective, as in FIG. 2E. The main portion 210 may be a surface formed when the cross-sectional shape defined by the medial-lateral curvature 220, the central extension 222, and optionally the wall 224 is swept along the arcuate path of the anterior-posterior curvature 230, as shown in FIG. 2E. Similarly, the talar articular surface 110 may be a surface formed when the cross-sectional shape defined by the medial-lateral curvature 220 and the anterior-posterior curvature 230 is swept along a similar arcuate path, as also shown in FIG. 2E.

[0070] The keel 212 may also have a bone-sparing shape. Specifically, the keel 212 may have a base portion 240 that is integral with the remainder of the talar prosthesis 102, and a penetration portion 242 that extends from the base portion 240 and penetrates the bone of the talus. The penetration portion 242 may have a generally semicircular periphery 244 at a cranial end of the penetration portion. The generally semicircular periphery 244 may aid in preserving bone by presenting a medial-lateral facing surface area to the bone that resists movement of the talar prosthesis 102 in a medial-lateral direction. The resistance to medial-lateral movement may be equivalent to the resistance provided by a keel with a rectangular cross-sectional shape, but does not require as much bone removal as a rectangular periphery.

[0071] In some alternative embodiments (not shown), fixation pegs may be used in addition to or in place of the keel 212. Such fixation pegs may have any size or shape known in the art. In some embodiments, the fixation pegs may be permanently affixed to the remainder of the talus-engaging surface 112. In other embodiments, the fixation pegs may be modular and may be attached to receiving features in the bone-engaging surface, such as attachment apertures. In yet other embodiments, the fixation pegs may be deployable in place and movable from a retracted position to an deployed position to facilitate placement of the talar prosthesis and / or reduce the amount of ankle distraction required for implantation.

[0072] 3A-3E are cranial, caudal, lateral, lateral, and anterior cross-sectional views of the tibial prosthesis 104. The tibial articular surface 120 may be shaped to mimic the shape of the natural tibial articular surface. In some embodiments, the tibial articular surface 120 may have two concave tibial curves 300 extending in a medial-lateral direction. The concave tibial curves 300 may be separated from each other by a convex tibial curve 302 extending in a medial-lateral direction. The concave tibial curves 300 and the convex tibial curves 302 are best seen in FIG. 3E, where the cut plane extends in a medial-lateral and cranio-caudal direction, i.e., parallel to the concave tibial curves 300 and the convex tibial curves 302.

[0073] In a central position of the ankle after arthroplasty is complete, the convex talar curve 200 of the talar prosthesis 102 may reside within the concave tibial curve 300 of the tibial prosthesis 104, and the convex tibial curve 302 of the tibial prosthesis 104 may rest within the concave talar curve 202 of the talar prosthesis 102. This is the arrangement depicted in FIG. 1C. As the tibia rotates medially or laterally relative to the talus, one of the concave tibial curves 300 may slide along an adjacent one of the convex talar curves 200 such that the other of the concave tibial curves 300 is displaced from the adjacent one of the convex talar curves 200. The configurations and operation of the talar articular surface 110 and the tibial articular surface 120 described herein are exemplary only, and in alternative embodiments, any arrangement of articular surfaces and motion paths known in the art may be used.

[0074] The tibial engaging surface 122 may be shaped to provide secure engagement with a prepared surface of the tibia, as shown and described below. In some embodiments, the tibial engaging surface 122 may have a main portion 310 and a keel 312 extending from the main portion 310. The main portion 310 may have a contour that helps the main portion 310 remain securely seated on the tibia while leaving many of the adjacent bones of the tibia intact. Thus, the tibial prosthesis 104 may be a "bone-sparing" prosthesis.

[0075] In some embodiments, the main portion 310 may have two medial-lateral curved portions 320 located at the edges of the tibial engaging surface 122, and a central extension 322 extending substantially straight in the medial-lateral direction between the two medial-lateral curved portions 320. The medial-lateral curved portions 320 and the central extension 322 are best seen in FIG. 3E, where a cut plane extends in the medial-lateral and cranio-caudal directions, i.e., parallel to the medial-lateral curved portions 320 and the central extension 322. The central extension 322 may optionally be slightly recessed relative to the medial-lateral curved portions 320 to define a wall 324 facing towards the keel 312. The wall 324 may be arranged in a circumferential manner and may act as a retaining wall for the bone cement when the tibial prosthesis 104 is implanted. If the tibial component is to be secured to the bone using a porous interface, the wall 324 may be used to accommodate the porous material.

[0076] The main portion 310 may also have an anterior-posterior curvature 330 extending in the anterior-posterior direction. Thus, the cross-sectional shape of the main portion 310 may be generally arcuate with a convex shape when viewed from a lateral perspective, as in FIG. 3C, and generally rectilinear when viewed from an anterior perspective, as in FIG. 3E. The main portion 310 may be a surface formed when the cross-sectional shape defined by the medial-lateral curvature 320, the central extension 322, and optionally the wall 324 is swept along the arcuate path of the anterior-posterior curvature 330, as shown in FIG. 3E. Similarly, the tibial articular surface 120 may be a surface formed when the cross-sectional shape defined by the medial-lateral curvature 320 and the central extension 322 is swept along a similar arcuate path, as also shown in FIG. 2E.

[0077] The keel 312 may also have a bone-sparing shape similar to that of the keel 212. Specifically, the keel 312 may have a base portion 340 integrally formed with the remainder of the tibial prosthesis 104, and a penetration portion 342 extending from the base portion 340 and penetrating the bone of the talus. The penetration portion 342 may have a generally semicircular periphery 344 at its cranial end. In some embodiments, fixation pegs may secure the tibial prosthesis 104 to adjacent bone, as described above in connection with the talar prosthesis 102.

[0078] A variety of instruments and methods may be used to prepare the receiving surfaces of the talus and tibia for receiving the talar prosthesis 102 and the tibial prosthesis 104, respectively. One exemplary instrumentation set, along with one exemplary method, is shown and described in connection with Figures 4-15. Those skilled in the art will appreciate that each of the implants, instruments, and methods described herein may be used independently of the others and / or in conjunction with alternative implants, instruments, or methods.

[0079] In some embodiments, it may be beneficial to prepare the talus and / or the tibia from an anterior approach (i.e., an approach where instruments are inserted into the joint space from the anterior side of the joint space). The anterior approach may be less invasive and may speed recovery time by minimizing trauma. Some known procedures have used a lateral approach to create an anterior-posterior curve on the prepared surface of the talus and / or the tibia to preserve more of the bone underlying the implant. However, known instruments generally cannot create an anterior-posterior curve from other approaches, such as an anterior approach.

[0080] According to some embodiments, a surgeon may begin the arthroplasty procedure by entering the anterior side of the ankle joint. This may be done, for example, by cutting and retracting tissue (at the anterior surface of the joint) on the anterior side of the joint space. The joint space may then be exposed. The surgeon may then attach one or more guide assemblies to the talus and / or the tibia to guide the movement of one or more cutting instruments.

[0081] In some instances, a talar guide assembly may first be secured to the talus and used to guide the movement of a cutting instrument to prepare the talus to receive the talar prosthesis 102. This is illustrated and described in connection with FIGS. 4A-12. A portion of the talar guide assembly may then be used to properly position a tibial guide assembly which may be aligned on the talar guide assembly and then secured to the tibia. This is illustrated and described in connection with FIGS. 13A-13C. The tibial guide assembly may be used to guide the movement of a cutting instrument to prepare the tibia to receive the tibial prosthesis 104. This is illustrated and described in connection with FIGS. 14A-15. The talar prosthesis 102 and the tibial prosthesis 104 may then be inserted and secured to the talus and the tibia, respectively. The resulting joint space after completion of the ankle arthroplasty is illustrated and described in connection with FIG. 16.

[0082] 4A-4C are cranial, caudal, and cranial perspective views, respectively, of a trial 400 that may be used to position a talar base 410 relative to a talus 420 through the use of a post 430, with the talar base 410 and post 430 assembled with the talus 420 and trial 400 in FIG. 4C. The talus 420 may have a natural articular surface 422 to be replaced via arthroplasty.

[0083] As shown, the trial 400 has a cranial portion 440 and a caudal portion 442. The cranial portion 440 may have a post attachment feature 444 that interfaces with a corresponding feature (not shown) on the post 430. As shown, the post attachment feature 444 may have an oval shape with an opening that may interface with a corresponding oval recess and / or boss on the post 430. The caudal portion 442 may have a talar base alignment feature 446 that mates with the talar base 410 to temporarily couple the trial 400 to the talar base 410 such that rotation of the trial 400 also rotates the talar base 410. The talar base alignment feature 446 may have a hole 448 and a rectangular boss 450 that surrounds the hole 448.

[0084] Further, the trial 400 may have an anterior end 460 and a posterior end 462. When the trial 400 is placed on the talus 420, the anterior end 460 may extend over the anterior and metatarsals of the talus 420 and the posterior end 462 may rest on the natural articular surface 422 of the talus 420. The anterior end 460 may have an anterior window 464 that can be used to visually align the anterior end 460 with the talus 420 and / or the metatarsals. The posterior end 462 may have a posterior window 456 that facilitates visualization of the natural articular surface 422 and / or alignment of the posterior end 462 with the natural articular surface 422. The posterior end 462 may also have a concave curvature 458 sized to allow the posterior end 462 to fit relatively snugly over the natural articular surface 422.

[0085] The post 430 may have a proximal end (not shown) and a distal end 470. The distal end 470 may have a trial receiver 472 with a trial attachment feature (not shown) that is securable to the post attachment feature 444 of the trial 400. The trial receiver 472 may also have a hole 474 that aligns with and allows access to the hole 448 of the talar base alignment feature 446 when the post 430 is attached to the trial 400. The proximal end of the post 430 may have an alignment feature, such as a pin, hole, or marking, that may be easily aligned with a landmark on the patient's leg proximal to the talus. In some embodiments, this landmark may be the tibial tubercle on the proximal end of the tibia. Thus, the post 430 may have a length sufficient to span substantially the entire length of the patient's tibia.

[0086] As the proximal end of the post 430 is rotated into a desired alignment with the tibial tubercle, the distal end may also rotate, causing the trial 400 to rotate on the talus 420. This rotation may also cause the talar base 410 to rotate into a desired orientation relative to the talus 420. The talar base 410 may then be secured to the talus 420, for example, through the use of pins 480 that are inserted through the talar base 410 and driven into the talus 420. The pins 480 may be oriented at an angle relative to one another such that the talar base 410 cannot slide along the pins 480 toward or away from the talus 420. After the talar base 410 is secured in place relative to the talus 420, the trial 400 and post 430 may be removed from the talar base 410.

[0087] 5A, 5B, and 5C are posterior, anterior, and anterior temporal perspective views, respectively, of the talar base 410 of FIG. 4C, where the talar base 410 is fixed to the talus 420. The talar base 410 may be designed as a stable attachment point for positioning and / or moving other instruments relative to the talus 420 and / or the tibia. The talar base 410 may have a stationary member 500 and a movable member 502 that may be movably coupled to the stationary member 500.

[0088] The immobile member 500 may have a bone attachment interface that facilitates attachment of the immobile member 500 to the talus 420. Any bone attachment feature known in the art may be used, and in the embodiment of Figures 5A-5C, the bone attachment interface may take the form of a series of passages 510 through which the pins 480 are inserted. The passages 510 may be oriented obliquely relative to one another such that the pins 480 are non-parallel to one another. Thus, when the pins 480 are in position, the position and orientation of the talus base 410 may be substantially fixed relative to the talus 420. There may be more passages 510 than are required for fixation of the talus base 410, so that the surgeon need only insert the pins 480 through the passages 510 that are positioned for optimal fixation of the pins 480 in the talus 420.

[0089] The stationary member 500 may also have a movable member interface that provides a movable coupling of the movable member 502 to the stationary member 500. As embodied in Figures 5A-5C, the movable member 502 rotates relative to the stationary member 500. In an alternative embodiment (not shown), instead of pure rotation, a foundation may have a movable member that translates and / or some combination of translation and rotation relative to the stationary member. Any movable coupling known in the art may be used, including but not limited to pin joints, slip joints, linkages, and the like.

[0090] 5A-5C, the movable member interface may take the form of a pair of arcuate slots 512 extending in anterior-posterior and cranio-caudal directions. The arcuate slots 512 may be centered about an axis 514 extending in a medial-lateral direction. As shown in FIG. 5C, the axis 514 may be located caudal and posterior to the arcuate slots 512. From the outwardly facing side of the stationary member 500, the arcuate slots 512 may be recessed into an arcuate groove 516 that follows the same arcuate path as the arcuate slots 512. Two or more sets of detents 518 may be formed on each side of the stationary member 500. The detents 518 may extend generally in a medial-lateral direction and may help control the range of motion of the movable member 502 relative to the stationary member 500, as described below.

[0091] Additionally, the immobile member 500 may have a trial interface that couples the immobile member 500 to the trial 400. It may be desirable for the trial interface to provide a fixed attachment between the immobile member 500 and the trial 400 such that the position and orientation of the trial 400 determines the position and orientation of the immobile member 500, and thus the position and orientation of the talar base 410.

[0092] 5A-5C, the trial interface may be a hole 520 residing within a rectangular recess 522. A fastener, such as a screw or bolt, may be inserted through the talar base alignment feature 446 of the trial 400. The fastener may be inserted through the hole 474 of the trial receiver 472 and the hole 448 of the talar base alignment feature 446 and secured to the hole 520. The rectangular recess 522 may receive the rectangular boss 450 of the talar base alignment feature 446 to ensure that when the post 430 and the trial 400 are attached to the immobile member 500, the immobile member 500 cannot rotate relative to the trial 400 or the post 430.

[0093] The movable member 502 may have a stationary member interface that cooperates with the movable member interface of the stationary member 500 to provide a movable coupling between the stationary member 500 and the movable member 502. The stationary member interface may be selected to provide a rotatable coupling between the stationary member 500 and the movable member 502.

[0094] 5A-5C, the stationary member interface may include a roller 530 that resides in the arcuate groove 516 and is rotatably secured to the body of the movable member 502 through the arcuate slot 512. There may be two of the rollers 530 in each of the arcuate grooves 516 to ensure that the movable member 502 is not free to rotate relative to the stationary member 500, but instead is predictably forced to rotate relative to the stationary member 500 as it moves along the arcuate groove 516. Thus, the movable member 502 may be forced to rotate relative to the stationary member 500 about the axis 514.

[0095] In addition to the rollers 530, the movable member 502 may have a guide knob 540 that protrudes from an inner or outer side of the movable member 502. In some embodiments, the guide knob 540 may be rotatable relative to the remainder of the movable member 502 such that the guide knob 540 can be tightened to frictionally engage the stationary member 500, thereby preventing relative rotation between the stationary member 500 and the movable member 502, or loosened to allow the movable member 502 to rotate relative to the stationary member 500. Thus, the surgeon can engage the guide knob 540 to temporarily fix the movable member 502 in the correct position relative to the stationary member 500 and perform a cut with the movable member 502 in its current position and orientation before disengaging the guide knob 540 to move the movable member 502 to a new position and orientation.

[0096] The movable member 502 also has an abutment (not shown) facing towards the stationary member 500, which is adapted to engage the detent 518 when the movable member 502 is in two or more predefined positions relative to the stationary member 500. The predefined positions may be, for example, desired forward and rearward limits of movement of the movable member 502 relative to the stationary member 500. For example, when the movable member 502 is positioned such that the abutment engages the detent 518 at the front of the stationary member 500, the engagement of the abutment with the detent 518 may prevent the movable member 502 from moving further in a forward direction relative to the stationary member 500. This may be the position depicted in Figures 5A to 5C. Similarly, when the movable member 502 is positioned such that the abutment portion engages with the rear detent 518 of the stationary member 500, the engagement of the abutment portion with the detent 518 can prevent the movable member 502 from moving further in a rearward direction relative to the stationary member 500.

[0097] Alternatively, the engagement of the abutment with the detent 518 may not define a limit of motion, but rather provide a tactile response that indicates to the surgeon that the movable member 502 has reached a front or rear reference position relative to the stationary member 500. Specifically, the engagement of the abutment with the detent 518 may be heard and / or felt by the surgeon as the abutment snaps or clicks into the detent 518. Thus, the surgeon may be aware that further forward or rearward motion of the movable member 502 relative to the stationary member 500 may cause the movable member 502 to pass a predetermined reference point.

[0098] The movable member 502 may also have an instrument holder attachment interface, or more specifically, a talar bar holder interface that may be attached to a talar bar holder that holds a cutting instrument in the form of a bar. The talar bar holder may have a base that may be attached to the talar bar holder interface, and thus the talar bar holder interface may also be referred to as a base attachment interface. The base attachment interface may be designed to secure the base to the movable member 502 such that the movable member 502 carries the base with it as it moves relative to the stationary member 500. As described below, the base attachment interface may also be used to attach an alignment block to the movable member 502 to facilitate alignment of the tibial base relative to the tibia.

[0099] 5A-5C, the base mounting interface may take the form of a pair of threaded holes 550 in the movable member 502. The threaded holes 550 may receive fasteners, such as screws or bolts, that may be used to hold the base in place on the movable member 502. The construction and operation of the talar bar holder is shown and described in connection with FIGS. 6A-11B.

[0100] 6A and 6B are anterior and posterior perspective views, respectively, of a talar bar holder 600 secured to the talar base 410 for holding a bar 610 against the talus 420. The talar base 410 and the talar bar holder 600 may combine to define a talar guide assembly that guides movement of the bar 610 relative to the talus 420 to form a preparation surface 620 on the talus 420 that is shaped to receive a prosthesis, such as the talar prosthesis 102 of FIGS. 1A-2E.

[0101] Specifically, the talar bar holder 600 may be secured to the movable member 502 of the talar base 410 such that the talar bar holder 600 is pivotable along the movable member 502 relative to the stationary member 500 and the talus 420. The talar bar holder 600 may also allow for further movement of the bar 610 (e.g., medial-lateral and cranio-caudal) to create a desired profile of the preparation surface 620. The use of the burr 610 is exemplary only, and one of ordinary skill in the art will appreciate that a variety of cutting instruments may be used to form the preparation surface 620. Such cutting instruments may include rotational and / or translational instruments such as burrs, reamers, reciprocating saws, etc.

[0102] As shown, the talar bar holder 600 may have a base 630 fixedly secured to the movable member 502 of the talar base 410, and an arm 640 that moves relative to the base 630. Movement of the arm 640 relative to the base 630 may allow the bar 610 to move in a medial-lateral direction on the talus 420, in addition to the anterior-posterior rotation provided by movement of the movable member 502 relative to the talus 420. The bar 610, along with additional bars that may be used in connection with the arthroplasty process, are described in more detail in connection with Figures 7A-8C.

[0103] 7A-7C are perspective, side, and cross-sectional plan views, respectively, of the bar 610. The bar 610 may have a body 700, a shaft 710, and a cutting element 720. An adapter 730 may be used to couple the bar 610 to the talar bar holder 600. The body 700 may be generally cylindrical in shape and may house a rotational motor (not shown), which may rotate the shaft 710 relative to the body 700, which may also be cylindrical in shape. The cutting element 720 may be carried on the shaft 710, such that rotation of the shaft 710 may rotate the cutting element 720.

[0104] The cutting element 720 and the shaft 710 may rotate about a cutting instrument axis 740 that is parallel to the length of the cutting element 720. The rotating element 720 may have a concave shape that facilitates the creation of a convex anterior-posterior curve from an anterior approach. Specifically, the cutting element 720 may have a proximal end 750, a distal end 760, and an intermediate section 770 between the proximal end 750 and the distal end 760. The proximal end 750 and the distal end 760 may both be enlarged relative to the intermediate section 770 and may share a maximum radius 780 perpendicular to the cutting instrument axis 740. The radius of the intermediate section 770 may be much smaller. The maximum radius 780 may be substantially the same as the radius of the medial-lateral curve present in the preparation surface 620 to be created on the talus 420 by the cutting element 720.

[0105] In a plane with the cutting instrument axis 740, the cutting element 720 can have an arcuate concave profile with a radius 782 defined by the change in diameter of the cutting element 720 from the proximal end 750 to the intermediate end 770 and then to the distal end 760. The radius 782 can be substantially the same as the radius of the anterior-posterior curvature of the preparation surface 620 to be formed on the talus 420 by the cutting element 720.

[0106] The adaptor 730 may have a flared proximal end 790, a cylindrical distal end 792, a pair of body mounting holes 794, and a pair of bar holder mounting bosses 796. The proximal end 790 may be hollow and sized to accommodate the body 700 of the bar 610. The cylindrical distal end 792 may likewise be sized to accommodate the shaft 710 and / or surrounding material of the bar 610. The body mounting holes 794 may facilitate secure attachment of the adaptor 730 to the bar 610. According to some examples, fasteners such as screws may be inserted into the body mounting holes 794 to secure the adaptor 730 to the bar 610. The bar holder mounting bosses 796 may be used to facilitate attachment of the adaptor 730, and thus the bar 610, to the talar bar holder 600 and / or tibial bar holder, as shown and described below.

[0107] According to some examples, the body 700 may be the body of a standard orthopedic burr or reamer, and the cutting element 720 and the adapter 730 may be used to customize such a standard orthopedic burr or reamer for formation of the preparation surface 620 from an anterior approach.

[0108] A variety of different cutting elements may be used in addition to or in place of the cutting element 720. Such cutting elements may have a convex or straight shape. Examples are shown and described in connection with Figures 8A-8C.

[0109] 8A-8C are side views of a bar 800, a bar 830, and a bar 860, respectively, according to various embodiments. The bars 800, 830, and 860 may each be used with an adapter 730, such as the adapter of FIGS. 7A-7C, and may have components similar to those of the bar 610, including a body 700 and a shaft 710. The bars 800, 830, and 860 may each be configured to rotate about a cutting instrument axis 740, such as the cutting instrument axis of the bar 610. However, the cutting elements of the bars 800, 830, and 860 may be configured differently.

[0110] Specifically, the burr 800 may have a straight, generally cylindrical cutting element 820. The cutting element 820 may have a diameter 822 suitable for cutting a space in the preparation surface 620 for the keel 212 of the talar prosthesis 102. The diameter of the cutting element 820 may likewise be suitable for cutting a space for the keel 312 of the tibial prosthesis 104.

[0111] The burr 830 may also have a straight, generally cylindrical cutting element 850 having a diameter 852 suitable for cutting a space in the preparation surface 620 for the shaft 710 of the burr 610, the burr 800, and / or the burr 860, for example. Thus, the burr 830 may be used as an introduction tool to provide a space through which the shaft 710 can move in a subsequent bone removal step.

[0112] The burr 860 may be used to create a concave anterior-posterior curvature in the tibia. Thus, the burr 860 may have a generally convex cutting element 880. Specifically, the cutting element 880 may have a proximal end 882, a distal end 884, and an intermediate portion 886 between the proximal end 882 and the distal end 884. The intermediate portion 886 may be enlarged relative to the proximal end 882 and the distal end 884 and may have a maximum radius 888 perpendicular to the cutting instrument axis 740. The radii of the proximal end 882 and the distal end 884 may be much smaller. The maximum radius 888 may be substantially the same as the radius of the medial-lateral curvature present in the preparation surface to be created on the tibia by the cutting element 880.

[0113] In a plane with the cutting instrument axis 740, the cutting element 880 can have an arcuate convex profile with a radius 890 defined by the change in diameter of the cutting element 880 from the proximal end 882 to the intermediate end 886 and then to the distal end 884. The radius 890 can be substantially the same as the radius of the anterior-posterior curvature of the preparation surface to be created on the tibia by the cutting element 880.

[0114] 9A-9C are cranial, caudal, and anterior cross-sectional views, respectively, of the talar bar holder 600 of FIGS. 6A and 6B. The talar bar holder 600 can be designed to hold one or more cutting instruments to facilitate formation of the preparation surface 620 on the talus 420.

[0115] Specifically, the talar bar holder 600 may be used to hold the bar 830 to remove the anterior portion of the natural articular surface 422, thereby providing space for the shaft 710 of the bar 610 and the shaft 710 of the bar 800. The talar bar holder 600 may then be used to hold the bar 610 to remove the remaining portion of the natural articular surface 422 of the talus 420, thereby forming the convex anterior-posterior curvature of the preparation surface 620. The talar bar holder 600 may also be used to form a slot generally in the shape of the keel 212 of the talar prosthesis 102. Thus, after use of the talar bar holder 600 in combination with the bar 830, the bar 610, and the bar 800, the preparation surface 620 may be shaped to receive the talar engaging surface 112 of the talar prosthesis 102. These steps may be reordered and will be described in more detail below.

[0116] The base 630 of the talus bar holder 600 may have a base interface that can be used to attach the base 630 to the talus base 410. The base interface may have any structure suitable for securing the base 630 to the talus base 410. As embodied in FIGS. 9A-9C, the base interface may include two holes 900 spaced apart in a manner similar to the spacing between the screw holes 550 of the movable member 502 of the talus base 410. The holes 900 may be smooth bores. Thus, a fastener 902, which may be a screw, bolt, or the like, may be inserted through the holes 900 and rotated to engage the screw holes 550 of the movable member 502 of the talus base 410 to secure the base 630 to the movable member 502.

[0117] The base 630 may further include an arm coupling feature that couples the arm 640 to the base 630. The base 630 and the arm 640 may be movably coupled to one another through any combination of rotary and / or slip joints. According to some embodiments, the arm coupling feature provides a rotatable coupling between the base 630 and the arm 640.

[0118] As shown in FIGS. 9A-9C, the arm coupling feature may include a pin 910 to which the arm 640 is rotatably mounted. The pin 910 may have a head 912 and a shank 914 with male threads that engage with corresponding female threads in a hole 916 in the base 630. The head 912 may have an interface that allows the head 912 to be rotated by an instrument, such as a screwdriver, to facilitate assembly of the talar bar holder 600. The head 912 may reside in a hole 918 in the base 630. A portion of the shank 914 adjacent the head 912 may be smooth to allow the arm 640 to engage and rotate smoothly thereon. The base 630 may further include two parallel plates, an anterior plate 920 and a posterior plate 922, between which the proximal end of the arm 640 is captured. The hole 918 in which the head 912 resides may be formed in the front plate 920, and the hole 916 in which the shank 914 is seated may be formed in the rear plate 922. Thus, the pin 910 may be inserted rearwardly through the hole 918 in the front plate 920 to seat within the hole 916 in the rear plate 922.

[0119] Additionally, the base 630 may have a base guide feature that helps guide the movement of the arm 640 relative to the base 630. The base guide feature may cooperate with a corresponding arm guide feature of the arm 640 to limit the range of motion of the arm 640 and, therefore, the range of motion of the attached cutting instrument, such as the bar 610, the bar 800, or the bar 830, relative to the talus 420. As embodied in Figures 9A-9C, the base guide feature may include a rectangular window 930 with four guide surfaces 932. The guide surfaces 932, positioned caudally (and oriented to face the cranial direction), may help limit the movement of the cutting instrument in the caudal direction toward the talus 420, as described below.

[0120] As shown in FIG. 9C, the arm 640 may be divided into a first arm member 950 and a second arm member 952. The second arm member 952 may be nested within the first arm member 950 such that the second arm member 952 is slidable within the first arm member 950 such that the arm 640 effectively has an adjustable length relative to the pin 910. A resilient member may be used to bias the first arm member 950 away from the second arm member 952, thereby urging the arm 640 towards its maximum length. The resilient member may take the form of a linear spring 954 that is normally held under compression. The linear spring 954 may reside partially within a cavity at the tip of the second arm member 952.

[0121] The arm 640 may have a base coupling feature that couples the arm 640 to the base 630. The base coupling feature may be configured in a variety of ways and designed to cooperate with the arm coupling feature of the base 630. In Figures 9A-9C, the base coupling feature may include a slot 960 formed at a proximal end of the first arm member 950 and a cradle 962 formed at a proximal end of the second arm member 952. The slot 960 may be elongated in a cranial-caudal direction and may receive the pin 910 to allow the first arm member 950 to move upwardly or downwardly relative to the pin 910. The receiving base 962 may be concave and semicircular in shape so that the base end of the second arm member 952 presses up on the pin 910 and allows the first arm member 950 to urge downward, while allowing the base end of the second arm member 952 to abut and slide relatively smoothly against the pin 910.

[0122] The arm 640 may further include an instrument attachment interface to which a cutting instrument may be attached. When the cutting instrument is a bar, such as the bar 610, the bar 800, the bar 830, and / or the bar 860, the instrument attachment interface may be referred to as a bar attachment interface. The bar attachment interface may be designed to hold any of the bars 610, 800, 830 in a fixed relationship to the first arm member 950. More precisely, the bar attachment interface may be designed to receive and secure the adapter 730, which is secured to one of the bars 610, 800, 830.

[0123] 9A-9C, the bar mounting interface may take the form of a mounting cannula 970 with a lumen 972 sized to receive the cylindrical tip 792 of the adapter 730. The mounting cannula 970 may also have one or more locking features that can selectively lock the adapter 730 in position relative to the mounting cannula 970. The locking features may act as a bayonet-style attachment, and thus may take the form of axially and then circumferentially extending slots 974 on the mounting cannula. Each of the slots 974 may be sized to receive one of the bar holder mounting bosses 796 of the adapter 730.

[0124] Specifically, the adapter 730 may be attached to the corresponding cutting instrument and then inserted rearwardly into the mounting cannula 970 such that the bar holder mounting boss 796 enters the axially extending portion of the slot 974. Once the bar holder mounting boss 796 reaches the end of the axially extending portion, the adapter 730 may be rotated about the axis of the mounting cannula 970, which may be collinear with the cutting instrument axis 740 of the cutting instrument, such that the bar holder mounting boss 796 slides along the circumferentially extending portion of the slot 974. One or more snap features (not shown) may optionally snap the adapter 730 into the mounting cannula 970 in place. In any event, the combination of axial translation and rotation required to load the adapter 730 onto the loading cannula 970 can ensure that the cutting instrument is securely held relative to the first arm member 950 until the insertion motion is reversed.

[0125] Still further, the arm 640 may have an arm guide feature that cooperates with the base guide feature to constrain movement of the arm 640 relative to the base 630. The arm guide feature may be any member that can interact with the base guide feature to help constrain relative movement between the base 630 and the arm 640. Where the base guide feature includes a guide surface, the arm guide feature may advantageously be a follower that can abut and / or rest against such a guide surface.

[0126] Specifically, the base guide feature may be a post 980 that projects from the first arm member 950 between the pin 910 and the mounting cannula 970. The post 980 may project in an anterior direction such that the post 980 resides within the rectangular window 930 of the base 630. The interaction of the post 980 with the guide surface 932 of the rectangular window 930 may limit movement of the mounting cannula 970, and therefore the cutting instrument, to a generally rectangular area. In particular, the guide surface 932 at the bottom of the rectangular window 930 may limit movement of the cutting instrument toward the talus 420, thereby controlling the depth of resection.

[0127] More specifically, the guide surface 932 at the bottom of the rectangular window 930 may prevent the bar 610, the bar 800, and the cutting instrument shaft 740 of the bar 830 from moving closer to the talus 420 than a planar boundary. Similarly, the guide surface 932 at the side of the rectangular window 930 may prevent the bar 610, the bar 800, or the cutting instrument shaft 740 of the bar 830 from moving further inwardly or laterally than an additional planar boundary. Thus, the post 980 of the arm 640 may cooperate with the rectangular window 930 in the base 630 to ensure that the preparation surface 620 has a desired depth, width, and overall shape.

[0128] The action of the linear spring 954 may also help ensure that the preparation surface 620 has the desired shape. In particular, the pressure exerted by the linear spring 954 may help ensure that the cut made in the talus 420 extends to the maximum desired depth, thereby ensuring that the preparation surface 620 has the necessary depth and consistency to provide a continuous splay of bone to support the talar prosthesis 102. Even in this case, the linear spring 954 may be adjusted to provide a force that the surgeon can easily resist to remove bone with a shallower cut before extending the cutting instrument to the maximum depth allowed by the interaction of the post 980 with the rectangular window 930. The manner in which the talus cutting guide, including the talus base 410 and the talus bar holder 600, may be used to control the resection of the talus 420 is shown and described in more detail in connection with FIGS. 6A, 6B, and 10A-12.

[0129] 6A and 6B, the talar base 410 and the talar bar holder 600 may be used in some embodiments to form the preparation surface 620 starting from the posterior side of the preparation surface 620. Specifically, with the base 630 secured to the movable member 502 of the talar base 410 and the bar 830 secured to the arm 640, the movable member 502 may be pivoted relative to the stationary member 500 to a posterior position. This may position the cutting element 850 of the bar 830 above the posterior portion of the natural articular surface 422 of the talus 420. The surgeon may hold the bar 830 above the natural articular surface 422 against the force of the linear spring 954 with the post 980 displaced from the guide surface 932 at the bottom of the rectangular window 930 until the surgeon is ready to begin resecting the natural articular surface 422.

[0130] The surgeon may then lower the bar 830, causing the linear spring 954 to urge the bar 830 into engagement with the natural joint surface 422 until the post 980 rests against the guide surface 932 at the bottom of the rectangular window 930. The bar 830 may then be moved medially (i.e., side to side) by moving the loading cannula 970 medially, causing the post 980 to slide medially along the guide surface 932 at the bottom of the rectangular window 930. The post 980 may abut against the guide surfaces 932 on the right and left sides of the rectangular window 930 to control the range of medial and lateral movement of the bar 830.

[0131] Once the bar 830 has passed through the medial-lateral extent of the natural articular surface 422, the mobile member 502 may be rotated anteriorly relative to the stationary member 500 to move the bar 830 toward the anterior portion of the natural articular surface 422. The medial-lateral movement of the bar 830 may be repeated as necessary to remove material from the anterior portion of the natural articular surface 422. If desired, the medial-lateral movement of the bar 830 may also be performed during anterior rotation of the mobile member 502 to remove material from the entire anterior-posterior curve of the natural articular surface 422.

[0132] As previously mentioned, the purpose of the burr 830 may simply be to remove enough material to allow the burr 610 and the burr 800 to engage the talus 420 without obstruction, particularly by removing bone from where the shaft 710 of the burr 610 and the shaft 710 of the burr 800 will be placed in a later cutting step. Thus, the burr 830 need not be used to resect all of the natural articular surface 422.

[0133] Once the bar 830 has passed through the medial-lateral and anterior-posterior extents of the natural articular surface 422, it may be removed from the mounting cannula 970 and the bar 610 may be secured to the mounting cannula 970 instead. The bar 610 may then be positioned over the posterior portion of the natural articular surface 422. The surgeon may hold the bar 610 over the already partially resected natural articular surface 422 against the force of the linear spring 954. Again, the post 980 may be displaced from the guide surface 932 at the bottom of the rectangular window 930 until the surgeon is ready to begin resecting the natural articular surface 422 with the bar 610.

[0134] The surgeon may then lower the bar 610 and allow the linear spring 954 to urge the bar 610 into engagement with the natural joint surface 422 until the post 980 rests against the guide surface 932 at the bottom of the rectangular window 930. This is the position depicted in Figures 6A and 6B. The bar 610 may then be moved medially (i.e., side to side) by moving the loading cannula 970 medially and laterally, causing the post 980 to once again slide medially along the guide surface 932 at the bottom of the rectangular window 930. The post 980 may abut against the guide surfaces 932 on the right and left sides of the rectangular window 930 to control the range of medial and lateral movement of the bar 610.

[0135] Once the bar 610 has passed through the medial-lateral extent of the natural articular surface 422, the mobile member 502 may be rotated anteriorly relative to the stationary member 500 to move the bar 610 toward the anterior of the natural articular surface 422. This is the position depicted in Figures 10A and 10B.

[0136] 10A and 10B are anterior and posterior perspective views, respectively, of the talus 420 with the talar base 410 attached to the talus 420, the talar bar holder 600 attached to the talus base 410, and the bar 610 positioned to resect the anterior portion of the natural articular surface 422 of the talus 420. Medial-lateral motion of the bar 610 can be repeated as necessary to remove material from the anterior portion of the natural articular surface 422. If desired, medial-lateral motion of the bar 610 can also be performed during anterior rotation of the mobile member 502 to remove material from the entire anterior-posterior curvature of the natural articular surface 422.

[0137] As a result, the preparation surface 620 may be formed as depicted in Figures 6B and 10B, which is further shown and described in connection with Figures 11A and 11B.

[0138] 11A and 11B are a cross-sectional view and an enlarged cranial view, respectively, of the lateral surface of the talus 420 with the talar base 410, the talar bar holder 600, and the bar 610 positioned as in Figures 10A and 10B. The shape of the preparation surface 620, excluding the slot for the keel 212 of the talar prosthesis 102, is depicted in more detail.

[0139] As shown in FIG 11A, the preparation surface 620 may have a lateral cross-sectional shape in a plane lying in the anterior-posterior direction 130 and the cranio-caudal direction 134 that closely matches a side view of the talar prosthesis 102 as depicted in FIG 2C. The preparation surface 620 may have a convex anterior-posterior curvature 1100 with substantially the same radius as the anterior-posterior curvature 230 of the talus engaging surface 112 of the talar prosthesis 102. Anterior and posterior to the convex anterior-posterior curvature 1100, the preparation surface 620 may have two convex anterior-posterior curvatures 1110 that may have the same radius as the portion of the talus engaging surface 112 anterior and posterior to the anterior-posterior curvature 230.

[0140] 11B, the preparation surface 620 may have a cross-sectional shape in a plane lying in the medial-lateral direction 132 and cranio-caudal direction 134 that closely matches the cross-sectional shape of the talus engaging surface 112 of the talar prosthesis 102, as depicted in FIG 2E, except that a slot for the keel 212 of the talar prosthesis 102 has not yet been formed. The preparation surface 620 may have a generally linear (in cross-section) central extent 1120 and two concave medial-lateral curvatures 1130 on either side of the central extent 1120. The central extension 1120 may have a width generally equal to the width of the central extension 222 of the talus engaging surface 112 of the talar prosthesis 102, and the concave medial-lateral curvature 1130 may have a radius generally equal to the radius of the medial-lateral curvature 220 of the talus engaging surface 112 of the talar prosthesis 102.

[0141] The shape of the cutting elements 720 of the burr 610 may determine various configurational geometric parameters of the preparation surface 620. Specifically, the radius 782 along the length of the cutting tool axis 740 of the cutting elements 720 of the burr 610 may be substantially the same as the radius of the convex anterior-posterior curvature 1100. Similarly, the maximum radius 780 perpendicular to the cutting tool axis 740 of the cutting elements 720 of the burr 610 may be substantially the same as the radius of the concave medial-lateral curvature 1130.

[0142] As mentioned above, it may be desirable to form a slot in the preparation surface 620 to ensure that the surface 620 can receive the keel 212 of the talar prosthesis 102. Formation of a slot is optional, and in some embodiments, an ankle prosthesis may not have a keel or may have a keel that incorporates a cutting element that forms a slot in response to pressure of the keel against the bone. Additionally, in some embodiments, the slot may be formed prior to formation of the remainder of the preparation surface 620. Thus, for example, the burr 800 may be used to form the slot prior to use of the burr 610 to form the preparation surface 620 depicted in FIGS. 11A and 11B, and may also be used to form the slot prior to use of the burr 830. Formation of the slot is depicted in FIG. 12, assuming that the preparation surface 620 has already been formed as shown in FIGS. 11A and 11B.

[0143] 12 is a perspective view depicting the formation of a slot 1200 in the preparation surface 620 of the talus 420 using the bur 800. After completion of the previous bone removal step (or, optionally, prior to the performance of such step, as described above), the bur 800 may be attached to the mounting cannula 970 of the talus bar holder 600 with the talus bar holder 600 secured to the movable member 502 of the talus base 410. The bur 800 may then be positioned above a central portion of the preparation surface 620. The surgeon may hold the bur 800 above the preparation surface 620 against the force of the linear spring 954. Again, the post 980 may be displaced from the guide surface 932 at the bottom of the rectangular window 930 until the surgeon is ready to begin forming the slot in the preparation surface 620 with the bur 800.

[0144] The surgeon may then hold the burr 800 in a medial-lateral centered position and lower the burr 800, allowing the linear spring 954 to urge the burr 800 into engagement with the preparation surface 620 until the post 980 rests against the guide surface 932 at the bottom of the rectangular window 930. This is the position depicted in FIG. 12. As the cutting element 820 of the burr 800 is lowered onto the preparation surface 620, the cutting element 820 may form a slot 1200 substantially in the center of the preparation surface 620. The diameter 822 of the cutting element 820 may be generally equal to the width of the keel 212 of the talar prosthesis 102. The slot 1200 may have a caudal end (not visible) with a generally hemispherical, concave cross-sectional shape that closely receives the semicircular periphery 244 of the penetration 242 of the keel 212.

[0145] The keel 212 may interface with the slot 1200 in a manner that helps prevent the talar prosthesis 102 from moving in a medial-lateral direction relative to the preparation surface 620, and further facilitates secure attachment of the talar prosthesis 102 to the preparation surface 620. The keel 212 and / or the remainder of the talus engaging surface 112 of the talar prosthesis 102 may optionally have a porous and / or coated surface designed to promote bone ingrowth and adhesion. Additionally or alternatively, the talar prosthesis 102 may be designed for use with bone cement that forms a bond between the talus 420 and the talar prosthesis 102.

[0146] Once the preparation surface 620, including the slots 1200, is fully formed, the talar bar holder 600, along with any attached cutting instruments, may be removed from the talar base 410. The talar base 410 may remain in place on the talus 420, as in FIG. 5C. The talar base 410 may then be used to facilitate attachment of a tibial cutting guide to the tibia, as depicted in FIGs. 13A-13C.

[0147] 13A-13C are posterior caudal, anterior, and anterior temporal perspective views, respectively, of a tibial base 1300, also depicted in FIG. 13C as an alignment block 1310 for securing the tibial base 1300 to the tibia 1320. The talar base 410 may remain secured to the talus 420 as shown, and the alignment block 1310 is attached to the talar base 410 and the tibial base 1300 such that the tibial base 1300 is properly positioned relative to the joint.

[0148] Like the talar base 410, the tibial base 1300 can be part of a cutting guide that helps guide a cutting instrument relative to bone. A cutting instrument holder, such as a tibial bar holder, can be attached to the tibial base 1300 as shown and described below.

[0149] The tibial base 1300 may have a bone attachment interface that facilitates attachment of the tibial base 1300 to the tibia 1320. Any bone attachment feature known in the art may be used, and in the embodiment of Figures 13A-13C, the bone attachment interface may take the form of a series of passages 1330 through which the pins 480 are inserted. As with the talar base 410, the passages 1330 may be oriented obliquely relative to one another such that the pins 480 are non-parallel to one another. Thus, when the pins 480 are in place, the position and orientation of the tibial base 1300 may be substantially fixed relative to the tibia 1320. There may be more passages 1330 than are required for fixation of the tibial base 1300, so that the surgeon need only insert the pins 480 through the passages 1330 that are positioned for optimal fixation of the pins 480 in the tibia 1320.

[0150] The tibial base 1300 may also have an instrument holder attachment interface, or more specifically, a tibial bar holder interface that can be attached to a tibial bar holder that holds a cutting instrument in the form of a bar. The tibial bar holder may have a base that can be attached to the talar bar holder interface, and thus the talar bar holder interface may also be referred to as a base attachment interface. The base attachment interface may be designed to secure the base to the tibial base 1300. Unlike the talar base 410, the tibial base 1300 may not have a stationary member and a movable member, but rather, the entire tibial base may act as a stationary base for positioning the tibial bar holder. As depicted in FIG. 13C, the base attachment interface may also be used to attach the tibial base 1300 to the alignment block 1310 to facilitate positioning of the tibial base 1300 relative to the tibia 1320.

[0151] 13A-13C, the base attachment interface may take the form of a button 1340 with a threaded hole 1342 that may receive a threaded tip of a fastener for attaching the tibial bar holder or the alignment block to the button 1340. The button 1340 may also have an anterior rim 1344 and a posterior rim 1346 that cooperate to engage a slot 1350. More specifically, the slot 1350 may have a ledge 1352 that defines the keyhole shape of the slot 1350. The ledge 1352 may be between the anterior rim 1344 and the posterior rim 1346 such that the button 1340 may slide upwardly or downwardly within the slot 1350. The slot 1350 may have a cranial end 1354 that is absent the ledge 1352. The head end 1354 may thus provide a circular opening through which the front rim 1344 and the rear rim 1346 may pass to allow assembly of the button into a plate 1360 in which the slot 1350 is formed.

[0152] 13C, the alignment block 1310 can have a body 1370 with a talar base interface attachable to the talar base 410 and a tibial base interface attachable to the tibial base 1300. Each of the base interfaces can provide a secure fixation with the corresponding base such that the talar base 410 and the tibial base 1300 can be secured to one another in a predictable relative position.

[0153] 13C, the talar base interface may include two holes 1380 configured similarly to the two holes 900 of the talar bar holder 600. The holes 1380 may be spaced apart similarly to the spacing of the threaded holes 550 of the movable member 502 of the talar base 410 and may be smooth bores. Thus, a fastener such as the fastener 902 of the talar bar holder 600, which may be a screw, bolt, or the like, may be inserted through the holes 1380 and rotated into engagement with the threaded holes 550 of the movable member 502 of the talar base 410 to secure the alignment block 1310 to the movable member 502.

[0154] The tibial base interface may include a hole 1390, which may be a smooth bore like the hole 1380. A fastener, such as the fastener 902 of the talar bar holder 600, which may be a screw, bolt, or the like, may be inserted through the hole 1390 and rotated into engagement with the hole 1342 of the tibial base 1300 to secure the tibial base 1300 to the alignment block 1310.

[0155] The alignment block 1310 may first be secured to the talar base 410 by, for example, securing the holes 1380 to the threaded holes 550 of the movable member 502 with the fasteners 902. The movable member 502 may be positioned at a predictable location, such as at the anterior end of the movable member's 502 range of motion relative to the stationary member 500, when the alignment block 1310 is attached to the movable member 502. If desired, the movable member 502 may be locked in position relative to the stationary member 500, for example through the use of the guide knobs 540.

[0156] The tibial base 1300 may then be secured to the alignment block 1310 by fastening the holes 1390 to the holes 1342 of the tibial base 1300 with fasteners such as screws or bolts. In an alternative embodiment, the alignment block 1310 may first be secured to the tibial base 1300 and then secured to the talar base 410.

[0157] In either case, after attachment of the alignment block 1310 to the talar base 410 and the tibial base 1300, the tibial base 1300 can be in a predictable location relative to the talar base 410 and thus the ankle joint. The tibial base 1300 can then be used to guide the resection of the tibia 1320. The tibial base 1300 can then be secured to the tibia 1320 as shown by inserting a pin 480 through the passage 1330 of the tibial base 1300 and securing the tip of the pin 480 to the bone of the tibia 1320. Once the tibial base 1300 is secured to the tibia 1320, the alignment block 1310 can be removed from the talar base 410 and the tibial base 1300. The talus base 410 may also be removed from the talus 420 by withdrawing the pin 480 from the talus 420 .

[0158] The tibial base 1300 may then be used in combination with a tibial bar holder to define a tibial guide assembly that guides the bar relative to the tibia, as will be described in more detail with respect to Figures 14A-14C.

[0159] 14A, 14B, and 14C are anterior, lateral, and anterior temporal perspective views, respectively, of a tibial bar holder 1400 secured to the tibial base 1300 and the tibia 1320 in FIG. 14C. The tibial base 1300 and the tibial bar holder 1400 may combine to define a tibial guide assembly that guides movement of the bar 860 relative to the tibia 1320 to form a preparation surface on the tibia 1320 that is shaped to receive a prosthesis, such as the tibial prosthesis 104 of FIGS. 1A-1C and 3A-3E. Additionally, FIG. 15 is a lateral cross-sectional view of the tibial bar holder 1400 and the tibial base 1300 secured to the tibia 1320. The construction and operation of the tibial bar holder will be described in conjunction with FIGS. 14A to 15.

[0160] Specifically, the tibial bar holder 1400 may be secured to the hole 1390 of the tibial base 1300. The tibial bar holder 1400 may allow for movement of the bar 860 (e.g., medial-lateral and cranio-caudal) to create a desired contour of the preparation surface 1420 (shown in FIG. 15 ) of the tibia 1320. The use of the burr 860 is exemplary only, and one of ordinary skill in the art will appreciate that a variety of cutting instruments may be used to form the preparation surface 1420. Such cutting instruments may include rotational and / or translational instruments, such as burrs, reamers, reciprocating saws, etc.

[0161] As shown, the tibial bar holder 1400 can have a base 1430 fixedly secured to the tibial base 1300, and an arm 1440 that moves relative to the base 1430. Movement of the arm 1440 relative to the base 1430 can allow the bar 860 to move in a medial-lateral direction on the tibia 1320. The base 1430 and the arm 1440 can cooperate to provide constrained movement of a cutting instrument relative to the tibia 1320 in a manner similar to that of the talar bar holder 600, as described below.

[0162] The base 1430 of the tibial bar holder 1400 may have a base interface that can be used to attach the base 1430 to the tibial base 1300. The base interface may have any structure suitable for fastening the base 1430 to the tibial base 1300. As embodied in Figures 14A to 15, the base interface may include a hole 1450 that can align with the hole 1342 of the button 1340 of the tibial base 1300 such that a fastener 1452, such as a screw or bolt, can be inserted through the hole 1450 and rotated to engage the hole 1342 of the button 1340 of the tibial base 1300 to fasten the base 1430 to the tibial base 1300.

[0163] The base 1430 may further include an arm coupling feature that couples the arm 1440 to the base 1430. The base 1430 and the arm 1440 may be movably coupled to one another through any combination of rotating and / or slip joints. According to some embodiments, the arm coupling feature provides a rotatable coupling between the base 1430 and the arm 1440.

[0164] 14A-15, the arm coupling feature may include a pin 1460 to which the arm 1440 is rotatably mounted. The pin 1460 may have a head 1462 and a shank 1464 with male threads that may engage with corresponding female threads in a hole 1466 in the base 1430. The head 1462 may have an interface that allows rotation of the head 1462 by an instrument such as a screwdriver to facilitate assembly of the tibial bar holder 1400. The head 1462 may reside within a hole 1468 in the base 1430. A portion of the shank 1464 adjacent the head 1462 may be smooth to allow the arm 1440 to engage and smoothly rotate thereon. The base 1430 may further include two front plates 1470 and a rear plate 1472 between which the arm 1440 is generally captured. The hole 1468 in which the head 1462 resides may be formed in a top portion of the front plate 1470, and the hole 1466 in which the shank 1464 is seated may be formed in the rear plate 1472. Thus, the pin 1460 may be inserted rearwardly through the hole 1468 in the top portion of the front plate 1470 to seat within the hole 1466 in the rear plate 1472.

[0165] Additionally, the base 1430 may include a base guide feature that helps guide movement of the arm 1440 relative to the base 1430. The base guide feature may cooperate with a corresponding arm guide feature of the arm 1440 to limit the range of motion of the arm 1440, and thereby the range of motion of the attached cutting instrument, such as the bar 860, the bar 800, or the bar 830, relative to the tibia 1320. As embodied in FIGS. 14A-15, the base guide feature may include a notch 1480 with a number of guide surfaces 1482. One of the guide surfaces 1482 may be oriented to face in the caudal direction to limit movement of the cutting instrument in the cranial direction toward the tibia 1320, as described below. The remaining guide surfaces 1482 may be oriented in a medial-lateral direction to limit movement of the cutting instrument in the medial-lateral direction.

[0166] As shown in FIG. 15, the arm 1440 may be divided into a first arm member 1500 and a second arm member 1502. The second arm member 1502 may be nested within the first arm member 1500 such that the second arm member 1502 is slidable within the first arm member 1500 such that the arm 1440 effectively has an adjustable length relative to the pin 1460. A resilient member may be used to bias the first arm member 1500 away from the second arm member 1502, thereby urging the arm 1440 towards its maximum length. The resilient member may take the form of a linear spring 1504 that is normally held under compression. The linear spring 1504 may reside partially within a cavity at the distal end of the second arm member 1502. The first arm member 1500 may have an opening 1506 that allows the fastener 1452 to enter from the anterior side of the tibial bar holder 1400 .

[0167] The arm 1440 may have a base coupling feature that couples the arm 1440 to the base 1430. The base coupling feature may be configured in a variety of shapes and designed to cooperate with the arm coupling feature of the base 1430. In FIG. 15, the base coupling feature may include a slot 1510 formed in the first arm member 1500 and a cradle 1512 formed at the top end of the second arm member 1502. The slot 1510 may be elongated in a cranial-caudal direction and may receive the pin 1460 to allow the first arm member 1500 to move upwardly or downwardly relative to the pin 1460. The cradle 1512 may be concave and semicircular in shape so that the top end of the second arm member 1502 abuts and slides relatively smoothly against the pin 1460, while allowing the end of the second arm member 1502 to press down on the pin 1460 and urge the first arm member 1500 upward.

[0168] The arm 1440 may further have an instrument attachment interface to which a cutting instrument may be attached. When the cutting instrument is a bar, such as the bar 610, the bar 800, the bar 830, and / or the bar 860, the instrument attachment interface may be referred to as a bar attachment interface. The bar attachment interface may be designed to hold any of the bar 860, the bar 800, and the bar 830 in a fixed relationship to the first arm member 1500. More precisely, the bar attachment interface may be designed to receive and secure the adapter 730, which is secured to one of the bar 860, the bar 800, and the bar 830.

[0169] 14A-15, the bar mounting interface may take the form of a mounting cannula 970 that is substantially identical to the mounting cannula 970 of the talar bar holder 600. Thus, the mounting cannula 970 of the tibial bar holder 1400 may have an inner lumen 972 sized to receive the cylindrical tip 792 of the adapter 730. The mounting cannula 970 may also have one or more locking features that may selectively lock the adapter 730 in position relative to the mounting cannula 970. The locking features may act as bayonet-style attachments, and thus may take the form of axially and then circumferentially extending slots 974 on the mounting cannula. Each of the slots 974 may be sized to receive one of the bar holder mounting bosses 796 of the adapter 730. The adapter may be received and coupled to the mounting cannula 970 as described in connection with the talus bar holder 600 .

[0170] Still further, the arm 1440 may have an arm guide feature which cooperates with the base guide feature to constrain movement of the arm 1440 relative to the base 1430. The arm guide feature may be any member capable of interacting with the base guide feature to assist in constraining relative movement between the base 1430 and the arm 1440. Where the base guide feature includes a guide surface, the arm guide feature may advantageously be a follower which may abut and / or rest against such a guide surface.

[0171] Specifically, the base guide feature may be a post 1490 that projects from the first arm member 1500 between the pin 1460 and the mounting cannula 970. The post 1490 may project in an anterior direction such that the post 1490 resides within the notch 1480. The interaction of the post 1490 with the guide surface 1482 of the notch 1480 may limit the movement of the mounting cannula 970, and therefore the cutting instrument, to a generally rectangular area. In particular, the guide surface 1482 at the top of the notch 1480 may limit the movement of the cutting instrument toward the tibia 1320, thereby controlling the depth of resection.

[0172] More specifically, the guide surface 1482 on the top of the notch 1480 may prevent the cutting instrument shaft 740 of the bar 860, the bar 800, or the bar 830 from getting closer to the tibia 1320 than a planar boundary. Similarly, the guide surface 1482 on the side of the notch 1480 may prevent the cutting instrument shaft 740 of the bar 860, the bar 800, or the bar 830 from moving further inwardly or laterally than an additional planar boundary. Thus, the post 1490 of the arm 1440 may cooperate with the notch 1480 of the base 1430 to ensure that the preparation surface 1420 has a desired depth, width, and overall shape.

[0173] The action of the linear spring 1504 may also help ensure that the preparation surface 1420 has the desired shape. In particular, the pressure exerted by the linear spring 1504 may help ensure that the cut made into the tibia 1320 extends to the maximum desired depth, thereby ensuring that the preparation surface 1420 has the depth and consistency necessary to provide a continuous expanse of bone to support the tibial prosthesis 104. Even in this case, the linear spring 1504 may be adjusted to provide a force that the surgeon can easily resist in order to remove bone in a shallower cut before extending the cutting instrument to the maximum depth allowed by the interaction of the post 1490 with the notch 1480.

[0174] The tibial bar holder 1400 may be employed in a manner similar to that of the talar bar holder 600 to form the preparation surface 1420 on the distal end of the tibia 1320, except that the tibial bar holder 1400 does not have any moving parts and therefore does not require the cutting instrument to move in the anterior-posterior direction. Rather, the cuts may all be made at the same anterior-posterior reference point. Cutting may optionally begin with the burr 830 to remove enough bone to make room for the shaft 710 of the burr 860, and then cutting may continue with the burr 860 to form the contours of the preparation surface 1420, except for the slot for the keel 312 of the tibial prosthesis 104. The burr 800 may be used to form such a slot.

[0175] Similar to the talar bar holder 600, the linear spring 1504 is used to ensure that the proper depth of cut is obtained. Specifically, the surgeon may position the cutting element 850 of the bar 830 under the natural articular surface of the tibia 1320. The surgeon may hold the bar 830 under the natural articular surface against the force of the linear spring 1504 with the post 1490 displaced below the guide surface 1482 at the top of the notch 1480 until the surgeon is ready to begin resecting the natural articular surface.

[0176] The surgeon may then raise the bar 830 and allow the linear spring 1504 to push the bar 830 into engagement with the natural joint surface until the post 1490 rests against the guide surface 1482 at the top of the notch 1480. The bar 830 may then be moved medially (i.e., side to side) by moving the loading cannula 970 medially or laterally, causing the post 1490 to slide medially along the guide surface 1482 at the top of the notch 1480. The post 1490 may abut against the guide surfaces 1482 on the right and left sides of the notch 1480 to control the range of medial and lateral movement of the bar 830.

[0177] Once the bar 830 has passed through the medial-lateral extent of the natural articular surface, it may be removed from the mounting cannula 970 and the bar 860 may be secured to the mounting cannula 970 instead. The bar 860 may then be positioned beneath the natural articular surface of the tibia 1320. The surgeon may hold the bar 860 beneath the already partially resected natural articular surface against the force of the linear spring 1504. Again, the post 1490 may be displaced from the guide surface 1482 at the top of the notch 1480 until the surgeon is ready to begin resecting the natural articular surface with the bar 860.

[0178] The surgeon may then raise the bar 860 and allow the linear spring 1504 to push the bar 860 into engagement with the natural joint surface until the post 1490 rests against the guide surface 1482 at the top of the notch 1480. The bar 860 may then be moved medially (i.e., side to side) by moving the loading cannula 970 medially and laterally, causing the post 1490 to again slide medially along the guide surface 1482 at the top of the notch 1480. The post 1490 may abut against the guide surfaces 1482 on the right and left sides of the notch 1480 to control the range of medial and lateral movement of the bar 860.

[0179] The prepared surface 1420 may thus have a shape similar to that of the prepared surface 620 of the talus 420, with a concave anterior-posterior curvature 1592 instead of the convex anterior-posterior curvature 1100. A portion of the concave anterior-posterior curvature 1592 is depicted in FIG. 15. Referring briefly back to FIG. 11B, the prepared surface 1420 may have, in a plane parallel to the anterior-posterior direction 130 and the cranio-caudal direction 134, in addition to the concave anterior-posterior curvature 1592, two convex anterior-posterior curvatures 1110 located anterior and posterior to the concave anterior-posterior curvature 1592. Additionally, in a plane parallel to the medial-lateral direction 132 and the cranio-caudal direction 134, the prepared surface 1420 may have a central extension 1120 and two concave medial-lateral curvatures 1130 located on either side of the central extension 1120. Thus, once the slot for the keel 312 is formed, the preparation surface 1420 may have a shape that generally complements the shape of the tibial engaging surface 122 of the tibial prosthesis 104, as depicted in Figures 3A-3E.

[0180] Once the burr 860 has passed through the medial-lateral extent of the natural joint surface, it may be removed from the mounting cannula 970 and the burr 800 may instead be secured to the mounting cannula 970. The burr 800 may then be positioned under a center of the preparation surface 1420. The surgeon may hold the burr 800 under the preparation surface 1420 against the force of the linear spring 1504. Again, the post 1490 may be displaced from the guide surface 1482 at the top of the notch 1480 until the surgeon is ready to begin forming the slot in the preparation surface 1420 with the burr 800.

[0181] The surgeon may then hold the burr 800 in a medial-lateral centered position and raise the burr 800, causing the linear spring 1504 to urge the burr 800 into engagement with the preparation surface 1420 until the post 1490 rests against the guide surface 1482 at the top of the notch 1480. As the cutting element 820 of the burr 800 is raised onto the preparation surface 1420, the cutting element 820 may form a slot 1598 substantially in the center of the preparation surface 1420. The diameter 822 of the cutting element 820 may be generally equal to the width of the keel 312 of the tibial prosthesis 104. The slot 1598 may have a cranial end with a generally hemispherical, concave cross-sectional shape that snugly receives the semicircular periphery 344 of the penetration 342 of the keel 312.

[0182] The keel 312 may interface with the slot 1598 to help prevent the tibial prosthesis 104 from moving in a medial / lateral direction relative to the prepared surface 1420, and further to facilitate secure attachment of the tibial prosthesis 104 to the prepared surface 1420. The keel 312 and / or the remainder of the tibial engaging surface 122 of the tibial prosthesis 104 may optionally have a porous and / or coated surface designed to promote bone ingrowth and adhesion. Additionally or alternatively, the tibial prosthesis 104 may be designed for use with bone cement that forms a bond between the tibia 1320 and the tibial prosthesis 104.

[0183] Once the preparation surface 1420, including the slots 1598, is fully formed, the tibial base 1300 may be removed from the tibial base 1300 along with any attached cutting instruments. The tibial base 1300 may also be removed from the tibia 1320 to clear the joint space of any obstructions. The talar prosthesis 102 and the tibial prosthesis 104 are then positioned on the prepared surface 620 of the talus 420 and the prepared surface 1420 of the tibia 1320, respectively. The resulting configuration is shown and described in connection with FIG.

[0184] 16 is a lateral cross-sectional view depicting the talus 420 and the tibia 1320 with the talar prosthesis 102 secured to the prepared surface 620 of the talus 420 and the tibial prosthesis 104 secured to the prepared surface 1420 of the tibia 1320. The talar articular surface 110 may articulate with the tibial articular surface 120 in a manner that generally mimics the articulation of the natural ankle joint. The various curvatures of the prepared surfaces 620 and 1420, along with the matching curvatures of the talus engaging surface 112 and the tibial engaging surface 122, may help maintain the talar prosthesis 102 and the tibial prosthesis 104 in the correct position while preserving sufficient healthy bone to withstand the stresses experienced during use of the joint.

[0185] In some embodiments (not shown), a surgical navigation system and / or a surgical robotics system may be used to facilitate preparation of the talus 420 and / or the tibia 1320. Some of the steps described above may be automated. A surgical navigation system, surface mapping system, or the like may be used to identify the location and dimensions of the cuts to be made. The motion paths for the cuts on the talus 420 and the tibia 1320 may optionally be mechanized using, for example, a motorized system in addition to or in place of elements of the talus guide assembly and / or the tibial guide assembly. Such a motorized system may optionally mimic the motion constraints of the talus guide assembly and / or the tibial guide assembly and therefore approach and prepare the joint surface from an anterior approach as disclosed herein.

[0186] Ankle arthroplasty systems in alternative embodiments may include many different features. According to some exemplary embodiments, one or more of the following features may be included: (1) the ability to slide the tibial base proximally to allow for a more proximal (i.e., deeper) cut into the tibia, (2) a tibial base that can swing along an arc to improve anterior / posterior resection of the tibia, (3) the ability to adjust the varus / valgus and / or medial / lateral position at which the tibial cutting guide resects the tibia, (4) the use of set screws to facilitate attachment of the tibial cutting guide to the tibia, (5) the use of talus trials to facilitate proper positioning of the tibial resection, and (6) the use of patient-specific bone attachment interfaces for the talus and / or the tibia. These features are shown and described in connection with Figures 17A-26B.

[0187] Figure 17A is a perspective view of the talus 420 with a portion of the trial 400 of Figures 4A-4C positioned on the concave curvature 458 of the talus 420, including an alternative embodiment talar base 1710. The trial 400 may be used to position the talar base 1710 relative to the talus 420 in a manner similar to that described in connection with Figures 4A-4C.

[0188] 17B is a perspective view of the talus base 1710 of FIG. 17A , where the talus base 1710 is secured to the talus 420. The talus base 1710 may have a configuration similar to that of the talus base 410. However, the talus base 1710 may have a stationary member 1700 and a movable member 1702 that are configured somewhat differently than the stationary and movable members of the talus base 410.

[0189] Specifically, the stationary member 1700 may also be secured to the talus 420 by a pin 480 passing through a passageway 510 of the stationary member 1700. The stationary member 1700 may also have an arcuate slot 1712 centered about the axis 514. However, the arcuate slot 1712 may not have the arcuate groove 516 of the arcuate slot 512 of FIG. 5C. Furthermore, the detents 518 may be absent from the stationary member 1700. Instead, the stationary member 1700 may have a detent 1718 in the form of a circular groove located at the center of each of the arcuate slots 1712. The detent 1718 may be used to fix the position of the mobile member 1702 relative to the stationary member 1700 at the center point of the arcuate slot 1712, for example, when the tibial base is to be positioned relative to the talar base 1710. A circular fastener (not shown) may be coupled to the movable member 1702 and may reside within the detent 1718 to lock the movable member 1702 in the correct position relative to the stationary member 1700 .

[0190] The movable member 1702 may have rollers 530 that roll within the arcuate slots 1712 to allow the movable member 1702 to pivot about the axis 514. Instead of the threaded holes 550 in the movable member 502, the movable member 1702 may have two receiving slots 1750 extending proximally and opening at their proximal ends for receiving corresponding features of the talar bar holder, as shown and described in connection with Figures 18A and 18B. The movable member 1702 may further have threaded holes 1760 for receiving fasteners of the talar bar holder.

[0191] 18A, 18B, and 19, perspective and side cross-sectional views illustrate the talar base 1710 of FIGS. 17A and 17B with a talar bar holder 1800 secured to the movable member 1702 of the talar base 1710. The talar bar holder 1800 may have a similar configuration to the talar bar holder 600 of FIGS. 6A and 6B, except that the talar bar holder 1800 may be configured to mount to the movable member 1702 instead of the movable member 502 of FIGS. 5A-5C.

[0192] Specifically, the talus bar holder 1800 may have a base 1830 that is secured to the movable member 1702. The base 1830 may have a pair of flanges 1840 on medial and lateral edges that slide into the receiving slot 1750 of the movable member 1702. The base 1830 may have a hole 1850 that aligns with the threaded hole 1760 of the movable member 1702. The hole 1850 may receive a bolt 1860 having a threaded end that engages with threads in the threaded hole 1760 to secure the base 1830 to the movable member 1702. The hole 1850 may be elongated in an up and down direction to allow some proximal / distal adjustment of the position of the base 1830 relative to the movable member 1702, thereby allowing the surgeon to adjust the depth of the cut on the talus 420.

[0193] The talus base 1710 and the talus bar holder 1800 may cooperate to function in a manner similar to that of the talus base 410 and the talus bar holder 600 described above. The talus bar holder 1800 may have the arm 640 that moves relative to the base 1830 with constraint provided by the association between the arm 640 and the base 1830. The arm 640 may be coupled to the bar 610 to guide the movement of the bar 610 (or any of the other types of bars described above) to resect the talus 420 and form the preparation surface 620.

[0194] With the talar base 1710 in place, the tibial cutting guide may be referenced over the talar base 1710 and then secured to the tibia. An alignment block may be used for this purpose, as shown and described in connection with Figures 20A-22C.

[0195] 20A-20E, an alignment block 2010 is illustrated according to an alternative embodiment, which may be functionally similar to the alignment block 1310, but with some modifications with respect to additional functionality.

[0196] As shown, the alignment block 2010 can include a fixed component 2020, an adjustment arm 2022, and an alignment rod 2024. The fixed component 2020 can be secured to the movable member 1702 of the talar base 1710 in a manner that allows medial / lateral adjustment of the location of the alignment block 2010 relative to the movable member 1702. The adjustment arm 2022 can be coupled to the fixed component 2020 in a manner that allows varus / valgus adjustment of the orientation of the adjustment arm 2022 relative to the fixed component 2020. The adjustment arm 2022 can also be coupled to the tibial resection guide (shown in subsequent figures) in a manner that allows the position of the tibial resection guide to be adjusted distally / proximally relative to the adjustment arm 2022.

[0197] More specifically, the stationary component 2020 may have two mounting slots 2030 that receive set screws 2032. The set screws 2032 may have threaded ends that engage threads in the threaded holes 1760 of the movable member 1702. The mounting slots 2030 may be long enough to allow horizontal adjustment of the position of the stationary component 2020 relative to the movable member 1702. If desired, the stationary component 2020 may be secured in position relative to the movable member 1702 by tightening the screws 2032, and then subsequently adjusted by loosening the screws 2032, moving the stationary component 2020, and then tightening the screws 2032 with the stationary component 2020 in the new position.

[0198] The stationary part 2020 may also have a boss 2034 that protrudes from a body of the stationary part 2020 towards the adjustment arm 2022. The boss 2034 may have a threaded hole 2036. Additionally, the stationary part 2020 may have a threaded hole 2038 disposed above the boss 2034 that includes the threaded hole 2036. The stationary part 2020 may also have a cover 2040 disposed above the mounting slot 2030.

[0199] The adjustment arm 2022 may have a hole 2050 at its lower end through which a bolt 2052 may be inserted and screwed into engagement with the threaded hole 2036 of the boss 2034 of the fixed part 2020. The bolt 2052 may be rotatably present within the hole 2050 such that the adjustment arm 2022 may pivot about the axis of the bolt 2052 until the adjustment arm 2022 is locked in position relative to the fixed part 2020. The bolt 2052 may optionally be tightenable to press against the adjustment arm 2022, thereby precluding further rotation of the adjustment arm 2022 relative to the fixed part 2020.

[0200] Additionally, the adjustment arm 2022 may have an adjustment slot 2054 disposed above the hole 2050 with an elongated arc centered about the center of the hole 2050. The adjustment slot 2054 may receive a bolt 2056 that may be threaded into engagement with the hole 2038 of the fixed component 2020. The bolt 2056 may be loosely seated within the adjustment slot 2054 such that the engagement of the bolt 2056 with the adjustment slot 2054 allows the adjustment arm 2022 to rotate relative to the fixed component 2020, but the abutment of the bolt 2056 with the end of the adjustment slot 2054 limits the range of rotation of the adjustment arm 2022 relative to the fixed component 2020. This relative rotation between the adjustment arm 2022 and the fixed component 2020 may allow adjustment of the medial / lateral position of the resected surface of the tibia where the tibial prosthesis 104 is to be seated. The bolt 2056 may optionally be tightenable to compress the adjustment arm 2022 and thereby preclude further rotation of the adjustment arm 2022 relative to the fixed component 2020.

[0201] The adjustment arm 2022 may also have a tibial foundation mounting hole 2058 through which a tibial foundation mounting bolt 2060 may pass, such that a threaded end of the bolt engages a corresponding threaded hole on the tibial foundation (shown below). The threaded hole may optionally be on a vertically movable member, as in the case of the tibial foundation 1300 of FIGS. 13A and 13B, where the hole 1342 is formed in the button 1340 that slides vertically within the slot 1350. The tibial foundation mounting hole 2058 and the tibial foundation mounting bolt 2060 may thus couple the adjustment arm 2022 to the tibial foundation in a manner that allows adjustment of the vertical (i.e., proximal / distal) position of the tibial foundation on the tibia, and thereby the proximal / distal depth to which the tibia is resected.

[0202] The tibial base mounting bolt 2060 may optionally be tightened to compress the adjustment arm 2022, thereby precluding further rotation of the adjustment arm 2022 relative to the fixed component 2020 and / or preclude proximal / distal movement of the tibial cutting guide relative to the adjustment arm 2022. In some embodiments, tightening the tibial base mounting bolt 2060 may both preclude further rotation of the adjustment arm 2022 relative to the fixed component 2020 and preclude further proximal / distal sliding movement of the tibial base relative to the adjustment arm 2022. In this manner, the tibial base mounting bolt 2060 may optionally be tightenable to fix the position of the tibial base relative to the fixed component 2020. As previously described, the medial / lateral position of the fixed component 2020 relative to the movable member 1702 may be fixed via the set screw 2032.

[0203] The adjustment arm 2022 may further have a rod opening 2062 that receives the alignment rod 2024. More specifically, the alignment rod 2024 may have a proximal end 2070 and a distal end 2072. The distal end 2072 may be received within the rod opening 2062 such that the alignment rod 2024 is fixed in position relative to the adjustment arm 2022. The alignment rod 2024 may then be used to help adjust the position and / or orientation of the adjustment arm 2022 relative to the movable member 1702. In some examples, the distal end 2072 of the alignment rod 2024 may be aligned with the knee, the tibial tubercle, or another anatomical feature to ensure that the adjustment arm 2022 is properly positioned and properly oriented in the medial-lateral direction for varus / valgus adjustment. Optionally, the alignment rods 2024 may also be used to facilitate proper anterior / posterior alignment of the tibial base relative to the talar base 1710, as will be discussed later.

[0204] 21A, 21B, 22A, 22B, and 22C, perspective, side, front, perspective, and side cross-sectional views depict the talar base 1710 attached to the talus 420 and a tibial base 2110 positioned relative to the tibia 1320 through the use of the alignment block 2010 and a tibial trial 2120. FIG. 21A depicts the tibial base 2110 secured to the tibia 1320, and FIG. 22B depicts the tibial trial 2120 alone. As with the previous embodiment, a "tibial cutting guide" may include the tibial base 2110 attachable to the tibia 1320, and a tibial bar holder (shown below) attachable to the tibial base 2110.

[0205] The tibial base 2110 may have a structure similar to that of the talar base 1710. Thus, the tibial base 2110 may have a stationary member 2100 and a movable member 2102. The stationary member 2100 may have two arcuate slots 1712 similar to the arcuate slots 1712 of the stationary member 1700 of the talar base 1710. The movable member 2102 may have two side walls 2150 from which rollers 530 extend in a medial and lateral direction to reside within the arcuate slots 1712 of the stationary member 2100. Thus, the movable member 2102 may rotate about an axis 2114 relative to the stationary member 2100.

[0206] The movable member 2102 of the tibial base 2110 may also have a button 1340 and a slot 1350, which may be similar in configuration to those of the tibial base 1300 of Figures 13A and 13B. Thus, the button 1340 and the slot 1350 may provide proximal / distal adjustment of the position of the tibial base 2110 relative to the adjustment arm 2022 of the alignment block 2010. As shown most clearly in Figure 22C, the button 1340 may receive a threaded end of the tibial base mounting bolt 2060 that secures the adjustment arm 2022 to the movable member 2102 of the tibial base 2110.

[0207] The alignment block 2010 may be secured to the movable member 1702 of the talar base 1710 by first inserting the threaded end of the set screw 2032 into the threaded hole 1760 of the movable member 1702 of the talar base 1710 with the shank of the set screw 2032 in the mounting slot 2030 of the fixed member 2020, and then tightening the set screw 2032 with the fixed member 2020 in a desired medial / lateral position relative to the movable member 1702. If desired, the set screw 2032 may be loosened and the medial / lateral position of the fixed member 2020 may be adjusted relative to the movable member 1702. The set screw 2032 may then be retightened to secure the fixed member 2020 to the movable member 1702. If desired, the alignment rod 2024 of the alignment block 2010 can be aligned with an anatomical feature, such as the tibial tubercle, to facilitate this medial / lateral placement.

[0208] The adjustment arm 2022 may then be pivotally coupled to the fixed component 2020. This may be accomplished by inserting a threaded end of the bolt 2052 through the hole 2050 of the adjustment arm 2022 and tightening it into the hole 2036 in the boss 2034 of the fixed component 2020. As previously mentioned, some clearance may be left between the shank of the bolt 2052 and the hole 2050 to allow the adjustment arm 2022 to rotate relative to the fixed component 2020 to allow varus / valgus adjustment of the orientation of the tibial preparation surface relative to the talar preparation surface.

[0209] The threaded end of the bolt 2056 may then be inserted through the adjustment slot 2054 and into the hole 2038 of the fixation component 2020 and tightened into the hole 2038. As previously mentioned, sufficient clearance may be left between the shank of the bolt 2056 and the walls of the adjustment slot 2054 to allow the shank of the bolt 2056 to slide along an arcuate path between the ends of the adjustment slot 2054. This interaction may limit the range of pivotal movement of the adjustment arm 2022 relative to the fixation component 2020 and limit the varus / valgus adjustability between the fixation component 2020 and the adjustment arm 2022 to a predetermined acceptable range. If desired, the alignment rod 2024 of the alignment block 2010 may be aligned with an anatomical feature, such as the tibial tubercle, to facilitate this varus / valgus alignment.

[0210] The tibial base 2110 may then be secured to the adjustment arm 2022. As previously described, this may be done by inserting the threaded end of the tibial base mounting bolt 2060 through the hole 2050 of the adjustment arm 2022 and then threading the threaded end of the tibial base mounting bolt 2060 into engagement with the hole 1342 of the button 1340 of the movable member 2102 of the tibial base 2110. The button 1340 may slide proximally / distally within the slot 1350 until the head of the tibial base mounting bolt 2060 is tightened against the adjustment arm 2022, thus allowing proximal / distal adjustment of the position of the tibial base 2110 relative to the alignment block 2010 and the talar base 1710. Such proximal / distal adjustment may allow the surgeon to adjust the depth to which the tibia 1320 is resected. The tibial base attachment bolt 2060 may be tightened so that the head of the tibial base attachment bolt 2060 tightly abuts the adjustment arm 2022 to preclude further movement of the button 1340 within the slot 1350, thereby preventing further proximal / distal adjustment.

[0211] Further adjustment of the position of the tibial base 2110 relative to the talar base 1710 in the anterior / posterior direction may be facilitated through use of the tibial trial 2120. As shown most clearly in FIGS. 22B and 22C , the tibial trial 2120 may have a pseudotalar bearing component 2200 and a tibial adjustment component 2202.

[0212] The pseudotalar bearing component 2200 may be shaped to seat on the prepared surface 620 of the talus 420, which has been shaped as described above prior to attachment of the alignment block 2010 and the tibial base 2110 to the talar base 1710. The pseudotalar bearing component 2200 may thus have a bone apposition surface 2210 with the same shape as the talus engaging surface 112 of the talar prosthesis 102. The pseudotalar bearing component 2200 may also have an anterior / posterior groove 2220 that generally follows the shape of the talar articular surface 110 of the talar prosthesis 102.

[0213] The tibial adjustment component 2202 may have a curved bearing portion 2230 and an anterior tongue 2240. The curved bearing portion 2230 may have an arcuate shape with a radius of curvature that matches the radius of curvature of the anterior / posterior groove 2220 of the pseudotalar bearing component 2200. Thus, the curved bearing portion 2230 may be slidable anteriorly and posteriorly within the anterior / posterior groove 2220. The anterior tongue 2240 may protrude anteriorly to engage the alignment block 2010, as shown most clearly in FIG. 22C. More specifically, the anterior tongue 2240 may have a posterior projection 2250 and an anterior projection 2260. The rear protrusion 2250 and the front protrusion 2260 may be spaced apart from one another such that the bottom of the stationary component 2020 of the alignment block 2010 resides between the rear protrusion 2250 and the front protrusion 2260, as shown in FIG. 22C.

[0214] The tibial adjustment component 2202 may also have a pair of markers 2270 that may be positioned at predetermined anterior and posterior locations on the curved bearing portion 2230. The markers 2270 may be used by a surgeon to visualize the anterior / posterior position of the curved bearing portion 2230 relative to the talar bearing component 2200. If desired, the markers 2270 may be radiopaque such that they may be easily detected and viewed through the use of surgical imaging techniques such as fluoroscopy.

[0215] In surgery, the tibial trial 2120 may be positioned such that the anterior tongue 2240 engages the fixed component 2020 with the fixed component 2020 between the posterior projection 2250 and the anterior projection 2260, as shown most clearly in FIG. 22C. The tibial base 2110 may be locked such that the mobile member 2102 is in an intermediate position relative to the stationary member 2100, as shown most clearly in FIG. 21B. This may be accomplished by moving the mobile member 2102 to the intermediate position relative to the stationary member 2100 and then locking the roller 530 of the mobile member 2102 in the center of the arcuate slot 512 through the use of a fastener (not shown) that couples the roller 530 to the detent 1718 of the arcuate slot 512.

[0216] The talar base 1710 may initially be in an anterior position with the roller 530 of the movable member 1702 proximate the bottom of the arcuate slot 512 of the stationary member 1700, which is also seen most clearly in FIG. 21B. From this position, the movable member 1702 may be moved in an anterior direction, causing the alignment block 2010, the tibial adjustment component 2202 of the tibial trial 2120 (which is coupled to the fixed component 2020 of the alignment block 2010 as previously described), and the tibial base 2110 (which is not yet coupled to the tibia 1320) to rotate in an anterior direction. When the marker 2270 indicates that the curved bearing portion 2230 is generally in a mid-position relative to the anterior / posterior groove 2220 of the talar bearing component 2200 (i.e., centered anteriorly / posteriorly within the anterior / posterior groove 2220), the tibial base 2110 may be considered to be in the proper anterior / posterior position relative to the talar base 1710.

[0217] Once the tibial base 2110 is properly positioned medially / laterally, varus / valgus, proximal / distal, and anterior / posteriorly as described above, the tibial base 2110 may be secured to the tibia 1320. The immobile member 2100 may have a passageway 510 to receive a pin 480, such as the pin 480 that attaches the talus base 1710 to the talus 420.

[0218] To ensure that the position of the tibial base 2110 does not change during the process of fixing the tibial base 2110 to the tibia 1320 with the pin 480, a standoff screw 2180 may be used. The standoff screw 2180 may have a screw shank that is inserted into a threaded hole in the immobile member 2100 of the tibial base 2110 and a blunt end (not shown) that abuts the tibia 1320. Before fixing the tibial base 2110 to the tibia 1320 with the pin 480, the standoff screw 2180 may be inserted into the corresponding hole in the immobile member 2100 and advanced until the blunt end engages the tibia 1320 without penetrating the tibia 1320 significantly. Thus, the standoff screw 2180 may prevent the immobile member 2100 from approaching the bone when the pin 480 is driven into the tibia 1320. Similar standoff screws (not shown) may optionally be used in association with one or more talar components, such as the talar base 1710.

[0219] Once the tibial base 2110 is secured to the tibia 1320, the alignment block 2010 and the talar base 1710 may be detached from one another, from the tibial base 2110, and from the talus 420 and removed to create space for the resection of the tibia 1320. This may be accomplished through the use of a tibial bar holder 2300, which may be functionally and structurally similar to the talar bar holder 600 of Figures 6A and 6B. The tibial bar holder 2300 is shown in more detail in Figure 23.

[0220] 23, a perspective view depicts a tibial bar holder 2300 secured to the tibial base 2110 to hold a bar 860 relative to the tibia 1320. The tibial base 2110 and the tibial bar holder 2300 may combine to define a tibial guide assembly that guides movement of the bar 860 relative to the tibia 1320 to form a preparation surface on the 1320 shaped to receive a prosthesis, such as the tibial prosthesis 104 of FIGS. 1A-2E.

[0221] Specifically, the tibial bar holder 2300 may be secured to the movable member 2102 of the tibial base 2110 such that the tibial bar holder 2300, together with the movable member 2102, may be pivotable relative to the stationary member 2100 and the tibia 1320. The tibial bar holder 2300 may also allow for further movement of the bar 860 (e.g., medial-lateral and cranio-caudal) to create a desired contour of the preparation surface of the tibia 1320. The use of the burr 860 is exemplary only, and one of ordinary skill in the art will appreciate that a variety of cutting instruments may be used to create the preparation surface on the tibia 1320. Such cutting instruments may include rotational and / or translational instruments such as burrs, reamers, reciprocating saws, etc.

[0222] As shown, the tibial bar holder 2300 can have a base 2330 fixedly secured to the movable member 2102 of the tibial base 2110, and an arm 2340 that moves relative to the base 2330. Movement of the arm 2340 relative to the base 2330 can allow the bar 860 to move in a medial-lateral direction on the tibia 1320 in addition to the anterior-posterior rotation provided by movement of the movable member 2102 relative to the tibia 1320.

[0223] The base 2330 may further include an arm coupling feature coupling the arm 2340 to the base 2330. The base 2330 and the arm 2340 may be movably coupled to one another through any combination of rotary and / or slip joints. According to some embodiments, the arm coupling feature provides a rotatable coupling between the base 2330 and the arm 2340.

[0224] As shown in FIG. 23, the arm coupling feature may include a pin 2310 to which the arm 640 is rotatably mounted. The pin 2310 may have a head and a shank (not shown) with male threads that can engage with corresponding female threads in a hole (not shown) in the base 2330. The head may have an interface that allows rotation of the head by an instrument such as a screwdriver to facilitate assembly of the tibial bar holder 2300. The head may reside in a hole 2318 in the base 2330. A portion of the shank adjacent the head may be smooth to allow the arm 2340 to engage and rotate smoothly thereon. The base 2330 may further include two parallel plates, an anterior plate 2320 and a posterior plate 2322, between which a proximal portion of the arm 2340 is captured. The hole 2318 in which the head resides may be formed in the front plate 2320 and the hole in which the shank is seated may be formed in the rear plate 2322. Thus, the pin 2310 may be inserted rearwardly through the hole 2318 in the front plate 2320 to seat within the hole in the rear plate 2322.

[0225] Additionally, the base 2330 may have a base guide feature that helps guide the movement of the arm 2340 relative to the base 2330. The base guide feature may cooperate with a corresponding arm guide feature of the arm 2340 to limit the range of motion of the arm 2340 and, thereby, the range of motion of the attached cutting instrument, such as the bar 860, the bar 800, or the bar 830, relative to the tibia 1320. As embodied in FIG. 23, the base guide feature may include a rectangular recess 2328 with three guide surfaces 2332. The guide surfaces 2332, which are disposed in a cranial direction (and oriented in the caudal direction, i.e., facing downward in the view of FIG. 23), may help to limit the movement of the cutting instrument in the cranial direction toward the tibia 1320. The medially and laterally facing guide surfaces 2332 may limit medially / lateral movement of the cutting instrument, as described in more detail below.

[0226] Similar to the arm 640 of the talus bar holder 600, the arm 2340 may be divided into a first arm member 2350 and a second arm member (not visible). The second arm member may be nested within the first arm member 2350 such that the second arm member is slidable within the first arm member 2350 such that the arm 2340 effectively has an adjustable length relative to the pin 2310. A resilient member (not visible) may be used to bias the first arm member 2350 away from the second arm member, thereby urging the arm 2340 towards its maximum length. The resilient member may take the form of a linear spring (not visible) that is normally held under compression.

[0227] The arm 2340 may have a base coupling feature that couples the arm 2340 to the base 2330. The base coupling feature may be configured in a variety of ways and designed to cooperate with an arm coupling feature of the base 2330. The base coupling feature may optionally include a slot and pedestal, such as the slot 960 and the pedestal 962 of Figures 9A-9C.

[0228] The arm 2340 may further have an instrument attachment interface to which a cutting instrument may be attached. When the cutting instrument is a bar, such as the bar 860, the bar 800, the bar 830, and / or the bar 610, the instrument attachment interface may be referred to as a bar attachment interface. The bar attachment interface may be designed to hold any of the bar 860, the bar 800, and the bar 830 in a fixed relationship to the first arm member 2350. More precisely, the bar attachment interface may be designed to receive and secure the adapter 730, which is secured to one of the bar 860, the bar 800, and the bar 830.

[0229] 9A-9C, the bar mounting interface of FIG. 23 may take the form of a mounting cannula 970 with a lumen (not visible) sized to receive the cylindrical tip of the adapter 730. The mounting cannula 970 may also have one or more locking features that can selectively lock the adapter 730 in position relative to the mounting cannula 970. The locking features may act as a bayonet-style attachment as in FIG. 9A-9C.

[0230] Still further, the arm 2340 may have an arm guide feature which cooperates with the base guide feature to constrain movement of the arm 2340 relative to the base 2330. The arm guide feature may be any member capable of interacting with the base guide feature to assist in constraining relative movement between the base 2330 and the arm 2340. Where the base guide feature includes a guide surface, the arm guide feature may advantageously be a follower which may abut and / or rest against such a guide surface.

[0231] Specifically, the base guide feature may be a post 2380 that projects from the first arm member 2350 between the pin 2310 and the mounting cannula 970. The post 2380 may project in an anterior direction such that the post 2380 resides within the rectangular recess 2328 of the base 2330. The interaction of the post 2380 with the guide surface 2332 of the rectangular recess 2328 may limit movement of the mounting cannula 970, and therefore the cutting instrument, to an area that generally comprises a cephalad boundary of a rectangle. In particular, the guide surface 932 at the top of the rectangular recess 2328 may limit movement of the cutting instrument toward the tibia 1320, thereby controlling the depth of resection.

[0232] More specifically, the guide surface 2332 on the top of the rectangular recess 2328 may prevent the cutting instrument shaft 740 of the bar 860, the bar 800, or the bar 830 from moving closer to the tibia 1320 than a planar boundary. Similarly, the guide surface 2332 on the side of the rectangular recess 2328 may prevent the cutting instrument shaft 740 of the bar 860, the bar 800, or the bar 830 from moving further medially or laterally than an additional planar boundary. Thus, the post 2380 of the arm 2340 may cooperate with the rectangular recess 2328 of the base 2330 to ensure that the preparation surface of the tibia 1320 has a desired depth, width, and overall shape.

[0233] The action of the linear spring within the arm 2340 may also help ensure that the preparation surface of the tibia 1320 has the desired shape. In particular, the pressure exerted by the linear spring may help ensure that the cut made in the tibia 1320 extends to the maximum desired depth, thereby ensuring that the preparation surface has the necessary depth and consistency to provide a continuous splay of bone to support the tibial prosthesis 104. Even in this case, the linear spring may be adjusted to provide a force that the surgeon can easily resist to remove bone at a shallower cut before extending the cutting instrument to the maximum depth allowed by the interaction of the post 2380 with the rectangular recess 2328. Thus, the tibial cutting guide, including the tibial base 2110 and the tibial bar holder 2300, may be used to control the resection of the tibia 1320.

[0234] With the tibial bar holder 2300 secured to the tibial base 2110, the tibial base 2110 can be used to guide the movement of the tibial bar holder 2300 to resect the tibia 1320 to form the preparation surface on the tibia 1320 to receive the tibial prosthesis 104. The movable member 2102 of the tibial base 2110 can be unlocked from the intermediate position shown in FIG. 21B to allow the movable member 2102, and thus the tibial bar holder 2300 and the bar 860, to pivot anteriorly / posteriorly relative to the stationary member 2100 when reaming the tibia 1320. This anterior / posterior movement can allow the tibial preparation surface to have an anterior / posterior curvature that is longer than the length of the cutting element 880 of the bar 860.

[0235] The tibial base 2110 may be used to guide the movement of the bar 830, the bar 860, and / or the bar 800 in much the same manner as the talar base 1710 or the talar base 410 guides the movement of the bar 610, the bar 830, and / or the bar 800. The preparation surface of the tibia 1320 may be formed to begin in a posterior or anterior direction of the preparation surface. In some embodiments, the bar 830 may be applied first to make a relatively shallow cut in the tibia 1320 that paves the way for the bar 860 and / or the bar 800 to enter the joint space and make a deeper cut that can accommodate the shape of the tibial engaging surface 122 of the tibial prosthesis 104.

[0236] More specifically, similar to the talar base 1710 and the talar base 410, the surgeon can hold the bar 830 under the natural articular surface of the tibia 1320 against the force of the linear spring in the arm 2340 with the post 2380 displaced from the guide surface 2332 at the top of the rectangular recess 2328 until the surgeon is ready to begin resecting the natural articular surface of the tibia 1320.

[0237] The surgeon may then raise the burr 830 and allow the linear spring to push the burr 830 into engagement with the natural articular surface of the tibia 1320 until the post 2380 rests against the guide surface 2332 at the top of the rectangular recess 2328. The burr 830 may then be moved medially (i.e., side to side) by moving the loading cannula 970 medially and laterally, causing the post 2380 to slide medially and laterally along the guide surface 2332 at the top of the rectangular recess 2328. The post 2380 may abut against the guide surfaces 2332 on the right and left sides of the rectangular recess 2328 to control the range of medial and lateral movement of the burr 830.

[0238] Once the bar 830 has passed through the medial-lateral extent of the natural articular surface of the tibia 1320, the mobile member 2102 may be rotated anteriorly or posteriorly relative to the stationary member 2100 to move the bar 830 toward the opposing (i.e., anterior or posterior) portion of the natural articular surface of the tibia 1320. The medial-lateral movement of the bar 830 may be repeated as necessary to remove material from the opposing portion of the natural articular surface of the tibia 1320. If desired, the medial-lateral movement of the bar 830 may also be performed during anterior or posterior rotation of the mobile member 2102 to remove material from the entire anterior-posterior curve of the natural articular surface of the tibia 1320.

[0239] As previously mentioned, the purpose of the burr 830 may simply be to remove enough material to allow the burr 860 and / or the burr 800 to engage the tibia 1320 without obstruction, particularly by removing bone from where the shaft 710 of the burr 860 and the shaft 710 of the burr 800 will be placed in a later cutting step. Thus, the burr 830 need not be used to resect all of the natural articular surface of the tibia 1320.

[0240] Once the bar 830 has passed through the medial-lateral and anterior-posterior extent of the natural articular surface of the tibia 1320, the bar 830 may be removed from the mounting cannula 970 and the bar 860 may be secured to the mounting cannula 970 instead. The bar 860 may then be positioned over the anterior or posterior portion of the natural articular surface of the tibia 1320. The surgeon may hold the bar 860 against the force of the linear spring in the arm 2340 below the already partially resected natural articular surface of the tibia 1320. Again, the post 2380 may be displaced from the guide surface 2332 at the top of the rectangular recess 2328 until the surgeon is ready to begin resecting the natural articular surface of the tibia 1320 with the bar 860.

[0241] The surgeon may then raise the burr 860 and allow the linear springs in the arms 2340 to urge the burr 860 into engagement with the natural articular surface of the tibia 1320 until the post 2380 rests against the guide surface 2332 at the top of the rectangular recess 2328. The burr 860 may then be moved medially (i.e., side to side) by moving the loading cannula 970 medially and laterally, causing the post 2380 to again slide medially and laterally along the guide surface 2332 at the top of the rectangular recess 2328. The post 2380 may abut against the guide surfaces 2332 on the right and left sides of the rectangular recess 2328 to control the range of medial and lateral movement of the burr 860.

[0242] Once the bar 860 has passed through the medial-lateral extent of the natural articular surface of the tibia 1320, the mobile member 2102 may be rotated anteriorly or posteriorly, as applicable, relative to the stationary member 2100 to move the bar 860 toward the anterior or posterior portion of the natural articular surface of the tibia 1320. The bar 860 may be moved medially / laterally during this anterior-posterior movement to ensure that the preparation surface of the tibia 1320 is fully formed.

[0243] As with the prepared surface 620 of the tibia 420, it may be desirable to form a slot in the prepared surface of the tibia 1320 to ensure that the preparation can receive the keel 312 of the tibial prosthesis 104. Formation of a slot is optional, and in some embodiments, an ankle prosthesis may not have a keel or may have a keel that incorporates a cutting element that forms a slot in response to pressure of the keel against the bone. Additionally, in some embodiments, the slot may be formed prior to formation of the remainder of the prepared surface of the tibia 1320. Thus, for example, the burr 800 may be used to form the slot prior to use of the burr 860 to form the prepared surface of the tibia 1320, or even prior to use of the burr 830.

[0244] After completion of the previous bone removal step (or, optionally, before such step is performed, as described above), the bar 800 may be attached to the mounting cannula 970 of the tibial bar holder 2300, with the tibial bar holder 2300 secured to the movable member 2102 of the tibial base 2110. The bar 800 may then be positioned under a central portion of the prepared surface of the tibia 1320. The surgeon may hold the bar 800 under the prepared surface of the tibia 1320 against the force of the linear spring of the arm 2340. Again, the post 2380 may be displaced from the guide surface 2332 at the bottom of the rectangular recess 2328 until the surgeon is ready to begin forming the slot in the prepared surface of the tibia 1320 with the bar 800.

[0245] The surgeon may then hold the burr 800 in a central medial-lateral position and raise the burr 800, causing the linear springs in the arms 2340 to urge the burr 800 into engagement with the prepared surface of the tibia 1320 until the post 2380 rests against the guide surface 2332 at the top of the rectangular recess 2328. As the cutting element 820 of the burr 800 is raised over the prepared surface of the tibia 1320, the cutting element 820 may form a slot corresponding to the slot 1200 of FIG. 12 substantially in the center of the prepared surface of the tibia 1320. The diameter 822 of the cutting element 820 may be generally equal to the width of the keel 312 of the tibial prosthesis 104. The slot may have a cranial end with a generally hemispherical, concave cross-sectional shape that closely receives the semicircular periphery 344 of the piercing portion 342 of the keel 312 .

[0246] Thus, the preparation surface of the tibia 1320 may be formed with a shape that matches the shape of the tibial engagement surface 122 of the tibial prosthesis 104. Once the entire preparation surface of the tibia 1320 is formed, the tibial bar holder 2300 may be detached and removed from the tibial base 2110, and the tibial base 2110 may be detached and removed from the tibia 1320. The joint space may then be prepared to receive the talar prosthesis 102 and the tibial prosthesis 104.

[0247] In some embodiments, the talar prosthesis 102 and the tibial prosthesis 104 may be inserted along a generally posterior direction such that the keel 212 of the talar prosthesis 102 slides posteriorly into the slot 1200 of the face 620 of the talus 420 and the keel 312 of the tibial prosthesis 104 slides posteriorly into the corresponding slot of the prepared face of the tibia 1320. In particular, some additional cranial / caudal movement and / or rotation of the talar prosthesis 102 and / or the tibial prosthesis 104 may be applied to fully seat the talar prosthesis 102 and the tibial prosthesis 104 on their respective prepared faces. However, it is beneficial to minimize the amount of distraction required in the joint space. Therefore, it may be advantageous for the insertion vector of the talar prosthesis 102 and the tibial prosthesis 104 to be primarily posterior.

[0248] Additionally, it may be advantageous to have no protruding features on the talus 420 or the tibia 1320 having an anteriorly or posteriorly facing surface, as such features would require insertion into the bone along a cranial or caudal (i.e., proximal or distal) insertion vector, which may require excessive distraction of the joint space, and therefore injury to surrounding tissue, as the joint space is enlarged to accommodate the necessary cranial or caudal movement required to seat the talar prosthesis 102 and the tibial prosthesis 104.

[0249] In some embodiments, a guide mechanism may have patient-specific components that are custom-made to match a portion of a patient's anatomy. Such a guide mechanism may be fabricated for the talus and / or the tibia. One example of such a guide mechanism is shown and described in connection with Figures 24A-26B as follows.

[0250] 24A, 24B, and 24C are top, bottom, and side views, respectively, of a patient-specific mounting plate 2400 that may be used as part of a patient-specific guide mechanism for the talus, according to one embodiment. As shown, the patient-specific mounting plate 2400 may have an outward facing side 2410 that faces away from the bone, and a bone-facing side 2420.

[0251] The patient-specific mounting plate 2400 may have a bone attachment interface in the form of bone mounting holes 2430 located on each side of the patient-specific mounting plate 2400 between the outboard side 2410 and the bone-facing side 2420. The bone mounting holes 2430 may receive screws (shown below) that secure the patient-specific mounting plate 2400 to the talus 420. The bone mounting holes 2430 may optionally have countersinks 2460 as shown that receive the heads of the bone screws.

[0252] The patient-specific mounting plate 2400 may also have an interface at which the remaining portion of the talar base immobility member may be secured to the patient-specific mounting plate 2400. In FIGS. 24A and 24B, this interface consists of a pair of component mounting holes 2440 extending from the outboard side 2410 to the bone-facing side 2420. The component mounting holes 2440 may receive fasteners to attach the patient-specific mounting plate 2400 to another component, as shown and described below. The component mounting holes 2440 may optionally be threaded to receive threaded ends of fasteners used to secure the other component to the patient-specific mounting plate 2400.

[0253] 24B, the bone-facing side 2420 can have a contoured surface 2470 shaped to match the contour of a portion of the talus 420 to which the patient-specific mounting plate 2400 is to be attached, which can be a portion of the talus 420 anterior to and / or surrounding the natural articular surface 422. The contoured surface 2470 can be created through the use of any process known in the art. In some examples, the contoured surface 2470 can be created by exposing a proximal portion of the talus 420, taking a mold of the talus, and then creating a model that resembles the proximal portion of the talus 420. The model can be stamped into a malleable block to form the contoured surface.

[0254] In an alternative embodiment, CT scan data or other images of the talus 420 may be used to custom manufacture the patient-specific mounting plate 2400 with the contoured conforming surface 2470. For example, CT scan data may be used in a milling machine to form the contoured conforming surface 2470 in a block of metal, plastic, or other material. Alternatively, such CT scan data may be used in an additive manufacturing process to custom manufacture the patient-specific mounting plate 2400 with the contoured conforming surface 2470 that precisely matches the shape of the proximal surfaces of the talus 420.

[0255] In any case, the contoured surface 2470 is shaped to match the adjacent portion of the talus 420. Thus, the patient-specific mounting plate 2400 can fit snugly and securely on the talus 420 without any ambiguity as to where the patient-specific mounting plate 2400 should be attached. The step of aligning the patient-specific mounting plate 2400 with the talus 420 can be performed when the contoured surface 2470 is designed. If desired, measurements can be taken before the contoured surface 2470 is created to determine not only the shape of the contoured surface 2470, but also the exact location and orientation of the contoured surface 2470 within the patient-specific mounting plate 2400, which will lead to the formation of a preparation surface in the appropriate location and orientation on the talus 420.

[0256] 25A is a perspective view of the patient-specific mounting plate 2400 on the talus 420. As shown, the outward facing side 2410 faces upward, the bone facing side 2420 faces the talus 420, and the contoured surface 2470 is positioned against the area of ​​the talus 420 adjacent the natural articular surface 422. The shape of the contoured surface 2470 can precisely match the shape of the talus 420 against which it rests, so that the patient-specific mounting plate 2400 can fit onto the talus 420 in a unique position and orientation. The patient-specific mounting plate 2400 can be secured to the talus 420 through the use of bone screws 2590.

[0257] Figure 25B is a perspective view of the patient-specific mounting plate 2400 and talus 420 of Figure 24A with a stationary component 2500 secured to the patient-specific mounting plate 2400 to define an immobile member similar in function to the stationary member 500 of Figures 5A and 5B and the stationary member 1700 of Figures 17A and 17B. The stationary component 2500 may be secured to the patient-specific mounting plate 2400 through the use of screws (shown below).

[0258] The patient-specific mounting plate 2400 and the stationary component 2500 may cooperate with a movable member to define a talar base 2510. As shown, the movable member may be similar or identical to the movable member 1702 of the talar base 1710 of Figures 17A and 17B. Once assembled, the talar base 2510 of Figure 25B may operate similarly to the talar base 1710 of Figures 17A and 17B and may guide rotation of a bar about axis 2114.

[0259] 26A and 26B are top and side views, respectively, of the talar base 2510 of FIGS. 25A and 25B , with the talar bar holder 1800 secured to the mobile member defined by the patient-specific mounting plate 2400 and the stationary component 2500. As shown, the patient-specific mounting plate 2400 is secured to the stationary component 2500 through the use of screws 2600. The talar base 2510 may function in a manner similar to that of the talar base 1710 to guide the movement of the talar bar holder 1800 to cause the bar 610, the bar 800, and / or the bar 830 to resect the natural articular surface 422 and form the preparation surface 620 on the talus 420.

[0260] Figures 24A-26B depict the use of a patient-specific talar component. Those skilled in the art will recognize how a patient-specific tibial component can be formed through the use of the same principles. Such a component can be incorporated into a tibial base that can be functionally similar to the tibial base 1300 of Figures 13A-15, or functionally similar to the tibial base 2110 of Figures 21A-21C.

[0261] Those skilled in the art will recognize that the systems and methods described above represent only a few of the systems and methods by which ankle arthroplasty may be performed. Alternative methods, cutting instruments, guide assemblies, and implants may be used within the scope of the present disclosure.

[0262] Any method disclosed herein includes one or more steps or actions for performing the described method. The method steps and / or actions may be interchanged with one another. In other words, unless a specific order of steps or actions is required for proper operation of the embodiment, the order and / or use of the specific steps and / or actions may be modified.

[0263] References throughout this specification to "one embodiment" or "the present embodiment" mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, references to the phrase, or variations thereof, wherever they appear throughout this specification are not necessarily all referring to the same embodiment.

[0264] Similarly, in the above description of the embodiments, it should be understood that various features may be grouped together in a single embodiment, drawing, or description thereof for the purpose of streamlining the disclosure. This method of disclosure, however, should not be interpreted as reflecting an intention that any claim requires more features than are expressly recited in that claim. Rather, as the subsequent claims reflect, inventive aspects lie in a combination of fewer than all features of any single prior disclosed embodiment. Thus, the claims following this detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment. This disclosure includes all permutations of an independent claim with its dependent claim.

[0265] The reference in a claim to the term "first" with respect to a feature or element does not necessarily imply the presence of second or additional such features or elements. It will be apparent to those skilled in the art that changes may be made to the details of the above-described embodiments without departing from the underlying principles described herein.

[0266] Although specific embodiments and applications of the present application have been illustrated and described, the scope of the appended claims is not limited to the precise configuration and components disclosed herein. Various modifications, changes, and variations may be made in the arrangement, operation, and details of the methods and systems disclosed herein, which will be apparent to those skilled in the art.

Claims

1. In ankle arthroplasty systems, a talar articular surface shaped to replace the natural talar articular surface; and a talar joint prosthesis including a talar engaging surface shaped to engage the talar preparation surface of the talus; a tibial articular surface shaped to replace the natural tibial articular surface and to articulate with the talar articular surface; and a tibial joint prosthesis including a tibial engagement surface shaped to engage the tibial preparation surface of the tibia; The talus engaging surface is a first front-to-rear curved portion having a concave shape and extending in the front-to-rear direction; a first medial-lateral curved portion having a convex shape and extending in a medial-lateral direction; a second medial-lateral curved portion having a convex shape and extending in the medial-lateral direction; and a central extension extending substantially linearly along the medial-lateral direction between the first medial-lateral curved portion and the second medial-lateral curved portion; Including, The tibial engaging surface is a first front-to-rear curved portion having a convex shape and extending in the front-to-rear direction; a first medial-lateral curved portion having a convex shape and extending in a medial-lateral direction; a second medial-lateral curved portion having a convex shape and extending in the medial-lateral direction; and a central extension extending substantially linearly along the medial-lateral direction between the first medial-lateral curved portion and the second medial-lateral curved portion; Including, The talar articular surface is two convex talar curves extending in the medial-lateral direction; and a concave talar curve extending in the medial-lateral direction between the two convex talar curves; The tibial articular surface is two concave tibial curves extending in the medial-lateral direction; and a convex tibial curve extending in the medial-lateral direction between the two concave tibial curves; and The ankle arthroplasty system, wherein the talar joint surface and the tibial joint surface are further shaped such that, when the tibial joint prosthesis is centered on the talar joint prosthesis, the two concave tibial curves are substantially flush with the two convex talar curves.

2. The ankle arthroplasty system of claim 1 , wherein the first anterior-posterior curve extends along substantially the entire anterior-posterior length of the talus-engaging surface and the tibia-engaging surface.

3. the talus engaging surface and the tibia engaging surface further include a keel projecting from the first anterior-posterior curve and extending along the anterior-posterior direction, the keel comprising: a base portion secured or integrally formed with the talus engaging surface and the remainder of the tibia engaging surface; and The ankle arthroplasty system of claim 1 including a penetration extending from the base portion for penetrating the talus preparation surface or the tibial preparation surface, the penetration having a generally semicircular circumference.

4. The ankle arthroplasty system of claim 1 , wherein the talus engaging surface further includes a keel projecting from the first anterior-posterior curve and extending along the anterior-posterior direction.

5. The ankle arthroplasty system of claim 1 , wherein the tibial engaging surface further includes a keel projecting from the first anterior-posterior curve and extending along the anterior-posterior direction.

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