Mechanical ligament balancing device

Abstract

1. A device comprising: a first plate configured to interact with a first bony structure of a joint; a second plate configured to interact with a second bony structure of the joint opposite the first bony structure; and at least one mechanical actuation mechanism disposed between the first and second plates and configured to apply a distraction force along an axis between the first and second plates and urge the first and second plates away from each other, wherein the device has a range of motion ranging from a minimum distance between the first and second plates to a maximum distance between the first and second plates, and the mechanical actuation mechanism is configured to provide a substantially constant distraction force throughout the range of motion.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application is a related § 111(a) application to and claims the benefit of commonly owned, co-pending U.S. Provisional Patent Application No. 63 / 039,729, filed June 16, 2020, and entitled "Ligament Balancing Device."

[0002] The field of the invention relates to orthopedics, and more particularly to balancing devices used by surgeons to characterize peri-articular ligaments and capsular envelopes during surgery and to apply tension to the peri-articular ligaments and capsular envelopes during the same surgery. [Background technology]

[0003] Elastic ligament balancing devices are used to assist surgeons in assessing the proper tension in the ligament envelope surrounding a joint during surgery. FIG. 1 illustrates a conventional ligament balancing device. These devices (e.g., the device disclosed in U.S. Pat. No. 10,154,836) include a proximal plate element 100, a distal plate element 200, and an elastic member 300 positioned between the proximal plate 100 and the distal plate 200. The elastic member 300 is controlled by an expansion mechanism that uses an electrical source, an electromechanical source, a mechanical source, a pneumatic source, a hydraulic source, or any combination of these sources. Summary of the Invention

[0004] Conventional ligament balancing devices have several limitations. The first limitation relates to the limited adjustment range of the proximal plate 100 relative to the distal plate 200 with respect to height, defined as the distance between the proximal and distal plates 100 (e.g., 8-14 mm), and angular tilt, defined as the sagittal and / or coronal orientation of the proximal plate 100 relative to the distal plate 200 (e.g., ±6°). More importantly, the interdependence between these two parameters. Based on the current design, the full range of angular tilt is available only when the height exceeds a threshold value (e.g., at least 10-12 mm), as shown in FIG. 2A. As the height approaches a minimum value, the range of angular tilt decreases. FIG. 2B illustrates the limited available range of angular tilt when the height of one side of the conventional ligament balancing device is below the threshold value. FIG. 2C illustrates the absence of an available range of angular tilt when the height of one side of the conventional ligament balancing device is at a minimum (e.g., 8 mm). This limitation is particularly important with respect to bicompartmental joints (eg, during total knee replacement) where one compartment may be substantially narrower than the other.

[0005] The second limitation relates to the effect of the loading conditions between the considered joint and the mobile plate (i.e., proximal plate 100 or distal plate 200, depending on the designation) in the transverse plane on the height and angular tilt measurements. Regarding this limitation, there are two distinct sources of error. The first source of error relates to the location of the load relative to the telescoping member 300. Referring to Figure 3, which shows a profile diagram of a conventional ligament balancing device, the location of the load application affects the measured gap and / or angular tilt. For example, if the load application is located directly "inside" the telescoping transverse section (Area A), the effect is negligible. Area B: If the load application is located at the most posterior or most lateral part of the articular surface (Area B), the effect may not be clinically relevant (e.g., ~0.5 mm). If the load application is located at the most anterior part of the articular surface (Area C), the effect may be clinically relevant (e.g., >1 mm).

[0006] A third limitation relates to the source of error associated with positioning the device in the frontal (e.g., coronal) plane, as this affects the distribution of moment arms and therefore balance. Similar to the discussion above, this is particularly important for bicompartmental joints.

[0007] A fourth limitation relates to the difficulty of maintaining a true force control feedback loop for the telescopic members, so distraction force can vary depending on height. [Brief explanation of the drawings]

[0008] Some embodiments of the present invention are herein described, by way of example only, with reference to the accompanying drawings. Referring now in detail to the drawings, it is emphasized that the specific details shown are by way of example and for purposes of illustrative discussion of embodiments of the invention. In this regard, the description accompanying the drawings will make apparent to those skilled in the art how embodiments of the invention may be practiced.

[0009] [Figure 1] FIG. 1 shows a conventional ligament balancing device.

[0010] [Figure 2A] FIG. 2A shows the available range of tilts when the spacing (ie, height) of the ligament balancing device of FIG. 1 exceeds a threshold value.

[0011] [Figure 2B] FIG. 2B illustrates the available range of tilts when the spacing (ie, height) of the ligament balancing device of FIG. 1 is below a threshold value.

[0012] [Figure 2C] FIG. 2C shows the available range of tilt when the spacing (ie, height) of the ligament balancing device of FIG. 1 is at the high or low end of its spacing range.

[0013] [Figure 3] FIG. 3 is an alternative view of the conventional ligament balancing device of FIG.

[0014] [Figure 4] FIG. 4 illustrates a first exemplary ligament balancing device.

[0015] [Figure 5] FIG. 5 illustrates various types of operation of the exemplary ligament balancing device of FIG.

[0016] [Figure 6] FIG. 6 illustrates a second exemplary ligament balancing device.

[0017] [Figure 7] FIG. 7 illustrates a third exemplary ligament balancing device.

[0018] [Figure 8] FIG. 8 illustrates a fourth exemplary ligament balancing device.

[0019] [Figure 9A] FIG. 9A illustrates a representation of a fourth exemplary ligament balancing device product.

[0020] [Figure 9B] FIG. 9B shows a graph of the force exerted by the axial spring of the product shown in FIG. 9A.

[0021] [Figure 9C] FIG. 9C shows a graph of the force exerted by the canted springs of the product shown in FIG. 9A.

[0022] [Figure 9D] FIG. 9D shows a graph of the total force exerted by the axial and diagonal springs of the product shown in FIG. 9A.

[0023] [Figure 9E] FIG. 9E shows a schematic side view of the spring of the product shown in FIG. 9A.

[0024] [Figure 10A] FIG. 10A shows another product representation from one of the exemplary ligament balancing devices. [Figure 10B] FIG. 10B shows another product representation from one of the exemplary ligament balancing devices. [Figure 10C] FIG. 10C shows another product representation from one of the exemplary ligament balancing devices.

[0025] [Figure 11] FIG. 11 illustrates a fifth exemplary ligament balancing device.

[0026] [Figure 12A] FIG. 12A illustrates a sixth exemplary ligament balancing device. [Figure 12B] FIG. 12B illustrates a sixth exemplary ligament balancing device. [Figure 12C] FIG. 12C illustrates a sixth exemplary ligament balancing device. [Figure 12D] FIG. 12D illustrates a sixth exemplary ligament balancing device. [Figure 12E] FIG. 12E illustrates a sixth exemplary ligament balancing device. [Figure 12F] FIG. 12F illustrates a sixth exemplary ligament balancing device.

[0027] [Figure 13A] FIG. 13A shows an exemplary ligament balancing device and an exemplary compression handle.

[0028] [Figure 13B] FIG. 13B illustrates the workflow of an exemplary "tibia first" technique for total knee arthroplasty.

[0029] [Figure 14A] FIG. 14A illustrates the workflow of an exemplary "modified interval balancing" technique for total knee arthroplasty.

[0030] [Figure 14B] FIG. 14B illustrates an exemplary ligament balancing device and an exemplary spacer provided for use during a procedure such as that shown in FIG. 14A.

[0031] [Figure 15] FIG. 15 illustrates an exemplary "total femoral first" procedure for total knee arthroplasty.

[0032] [Figure 16] FIG. 16 shows an exemplary device adapted for use in a total ankle replacement.

[0033] [Figure 17A] FIG. 17A illustrates an exemplary device adapted for use in an anatomical total shoulder replacement procedure. [Figure 17B] FIG. 17B illustrates an exemplary device adapted for use in an anatomical total shoulder replacement procedure.

[0034] [Figure 18] FIG. 18 illustrates an exemplary device adapted for use in a reverse shoulder replacement procedure.

[0035] [Figure 19A] Figure 19A shows a photograph of the test setup.

[0036] [Figure 19B] Figure 19B shows a photograph of the test setup.

[0037] [Figure 19C] FIG. 19C shows a data table of the test data. DETAILED DESCRIPTION OF THE INVENTION

[0038] In some embodiments, the device includes a first plate configured to interact with a first bony structure of the joint, a second plate configured to interact with a second bony structure of the joint opposite the first bony structure, and at least one mechanical actuation mechanism disposed between the first and second plates and configured to apply a distraction force along an axis between the first and second plates to urge the first and second plates apart. The device is configured to have a range of motion ranging from a minimum distance between the first and second plates to a maximum distance between the first and second plates. The mechanical actuation mechanism is configured to provide a substantially constant distraction force throughout the range of motion.

[0039] In some embodiments, the substantially constant distraction force is within ±15% of the reference distraction force throughout the range of motion, hi some embodiments, the substantially constant distraction force is within ±10% of the reference distraction force throughout the range of motion.

[0040] In some embodiments, the at least one mechanical actuation mechanism includes a first actuation sub-mechanism and a second actuation sub-mechanism, the first actuation sub-mechanism configured to provide a first actuation sub-mechanism distraction force, and the second actuation sub-mechanism configured to provide a second actuation sub-mechanism distraction force that opposes the first differential sub-mechanism distraction force.

[0041] In some embodiments, the at least one mechanical actuation mechanism includes at least one axial compression spring oriented along an axis, where an axial distraction force imparted by the at least one axial compression spring along the axis increases as the first plate moves toward the second plate, and at least one oblique compression spring oriented obliquely relative to the axis, where an axial distraction force imparted by the at least one oblique compression spring along the axis decreases as the first plate moves toward the second plate. The axial distraction force imparted by the at least one axial compression spring and the axial distraction force imparted by the at least one oblique compression spring combine to generate a substantially constant distraction force. In some embodiments, the at least one oblique compression spring is pivotally coupled to the first plate and the second plate. In some embodiments, the device also includes a stabilization mechanism configured to maintain the first plate and the second plate substantially parallel to each other. In some embodiments, the at least one axial compression spring is a peripheral spring disposed around the stabilization mechanism.

[0042] In some embodiments, the at least one mechanical actuation mechanism includes a telescoping member connecting the first plate to the second plate and a spring positioned to apply a force to the telescoping member to bias the first plate away from the second plate. In some embodiments, the force applied by the spring increases as the first plate approaches the second plate, the telescoping member includes a pivot point, and the spring is configured such that a moment arm about the pivot point of the force applied to the spring decreases as the first plate approaches the second plate, thereby causing the spring to apply a substantially constant distraction force. In some embodiments, the device also includes a second spring. The device is configured such that the spring and the second spring are interchangeably positionable within the device. The additional spring is configured to apply an additional force different from the force applied by the spring, such that when the second spring is positioned within the device, the device applies an additional substantially constant distraction force different from the substantially constant distraction force. In some embodiments, the device includes an adjustment mechanism adjustable by a user to preload the spring, whereby adjustment of the adjustment mechanism adjusts the substantially constant distraction force. In some embodiments, the adjustment mechanism includes a set screw.In some embodiments, the spring is a leaf spring.

[0043] In some embodiments, the device is an integrated device. In some embodiments, the device is a modular device configured such that at least one of the first plate or the second plate is detachable from at least one mechanical actuation mechanism.

[0044] In some embodiments, the device is configured for use in a total knee replacement, a unilateral knee replacement, an anatomical shoulder replacement, a reverse shoulder replacement, or an ankle replacement.

[0045] In some embodiments, the device also includes a second first plate configured to interact with a first bony structure of the joint, and a second mechanical actuation mechanism disposed between the second first plate and the second plate and configured to apply a second distraction force along an axis between the second first plate and the second plate, urging the second first plate and the second plate away from each other. The device is configured to have a range of motion ranging from a minimum distance between the second first plate and the second plate to a maximum distance between the second first plate and the second plate. The second mechanical actuation mechanism is configured to provide a substantially constant distraction force throughout the range of motion. In some embodiments, the second distraction force is different from the distraction force.

[0046] In some embodiments, the mechanical actuation mechanism is at least partially embedded in one of the first plate or the second plate.

[0047] In some embodiments, the device is sized to be placed within a joint cavity within a joint.

[0048] In some embodiments, the mechanical actuation mechanism is disposed within the periphery of the first plate and within the periphery of the second plate.

[0049] In some embodiments, the kit includes a first device and a second device. In some embodiments, the substantially constant distraction force of the first device is greater than the substantially constant distraction force of the second device. In some embodiments, the first device and the second device are configured to be coupled to each other at their respective second plates such that the distraction force of the first device and the distraction force of the second device are parallel to each other.

[0050] In some embodiments, the kit includes a plurality of first plates configured to interact with a first bony structure of a joint, a first of the plurality of first plates having a different size than a second of the plurality of first plates; a plurality of plate assemblies including a second plate each configured to interact with a second bony structure opposite the first bony structure of the joint; and at least one mechanical actuation mechanism secured to the second plate, the at least one mechanical actuation mechanism configured to be positioned between the second plate and selected ones of the plurality of first plates and coupled to the selected ones of the first plates to form an assembly device whereby the at least one mechanical actuation mechanism applies a distraction force along an axis between the selected ones of the first plates and the second plates to urge the selected ones of the first plates away from each other. The assembly device is configured to have a range of motion ranging from a minimum distance between the selected ones of the first plates and the second plates to a maximum distance between the selected ones of the first plates and the second plates. The at least one mechanical actuation mechanism is configured to provide a substantially constant distraction force throughout the range of motion.

[0051] In some embodiments, a method includes providing a device including a first plate configured to interact with a first bony structure of a joint, a second plate configured to interact with a second bony structure of the joint opposite the first bony structure, and at least one mechanical actuation mechanism disposed between the first and second plates and configured to apply a distraction force along an axis between the first and second plates to urge the first and second plates apart, wherein the device is configured to have a range of motion ranging from a minimum distance between the first and second plates to a maximum distance between the first and second plates, and the mechanical actuation mechanism is configured such that the distraction force is a substantially constant distraction force throughout the range of motion; performing a bone cut in the patient's joint to create a bone cut; positioning the device within the patient's joint such that the second plate abuts the cut; and characterizing laxity of ligaments in the patient's joint while the device is disposed within the joint.

[0052] Exemplary embodiments relate to ligament balancing devices that address the aforementioned weaknesses. In some embodiments described herein, the exemplary ligament balancing device is described with reference to an entire knee joint. In such devices, a first plate (e.g., a proximal plate) is configured to contact the patient's femur (e.g., the patient's natural femur), a trial femoral component, or a femoral component, depending on the stage of surgery (e.g., whether performed before or following femoral resection), and a second plate (e.g., a distal plate) is configured to contact the proximal end of the patient's tibia (e.g., the cut surface of the proximal end of the tibia). However, it will be apparent to those skilled in the art that the broader principles of the present disclosure apply to any joint. For example, it will be apparent to those skilled in the art that the exemplary embodiment can be divided into two symmetrical halves at the level of the sagittal plane, with specific sub-components on each side being used for a portion of the knee joint where the cruciate ligaments are maintained, or for the entire knee joint. Similarly, it will be apparent to those skilled in the art that the exemplary ligament balancing device may be adapted for use in other joints, such as the shoulder (in which case the first plate may be a central plate and the second plate a lateral plate, or vice versa), the ankle, the hip, the elbow, etc. The embodiments described herein use the term "plate" to refer to various elements adapted to act as contact points between the exemplary ligament balancing device described herein and the bony surfaces of the joint. It will be apparent to those skilled in the art that the particular shapes of the plates described herein are merely exemplary, and that other different shapes of contact elements are possible without departing from the broader concepts disclosed herein. For example, a plate need not include a continuous and / or uninterrupted contact surface, but may include one or more holes or other discontinuities therein.

[0053] 4 illustrates a first exemplary ligament balancing device 400. In some embodiments, the exemplary ligament balancing device includes two separate first plates 410, 420, where the first first plate 410 is intended to engage a first condyle of the femur and the second first plate 420 is intended to engage a second condyle of the femur. In some embodiments, a first telescoping member 430 is located between the first first plate 410 and a second second plate 450, and a second telescoping member 440 is located between the second first plate 420 and the distal plate 450. The first telescoping member 430 and the second telescoping member 440 may be controlled by the same telescoping mechanism or separate telescoping mechanisms. In such embodiments, the range of angular tilt is not associated with (and therefore not limited by) a height value. For example, as shown in FIG. 5, when one first plate 410 is in a fully depressed position relative to the second plate 450, the second first plate 420 can still independently self-adjust over the full range of height depending on ligament relaxation.

[0054] FIG. 6 illustrates a second exemplary ligament balancing device 600. The second embodiment includes a stabilization mechanism 610 (e.g., a hinged lever arm, a telescoping post) that constrains the degrees of freedom of the first and second plates 620, 630 relative to the second plate 640. In some embodiments, the only degree of freedom of the first plates 620, 630 relative to the distal plate 640 relates to movement along an axis substantially perpendicular to the contact surface of the second plate 640, which should be equal to the proximal-distal axis in the absence of posterior tibial slope and varus / valgus of the proximal tibial cut. In some embodiments, the contact surfaces of the first plates 620, 630 are substantially flat (e.g., as shown in FIG. 6 ), while in other embodiments, the contact surfaces of the first plates 620, 630 are essentially convex or concave, which, for a device 600 adapted for use in a total knee arthroplasty, mimics the anatomy of the proximal end of the natural tibia.

[0055] As a result of exemplary embodiments such as the embodiment described above with reference to FIG. 6 (i.e., (1) limiting the degree of freedom of the first plate 620, 630 relative to the second plate 640 to movement along a single axis substantially perpendicular to the contact surface of the second plate 640, and (2) making the contact surfaces of the first plates 620, 630 substantially flat, essentially convex, or essentially concave), four advantages can be achieved. First, in some embodiments, the ligament balancing device 600 allows for the accurate gap measurement throughout the range of motion to be defined as the distance from the most distal point of each condyle to the simulated proximal tibial cut, which is not achievable with conventional ligament balancing devices because the angular inclination of the proximal plate does not allow for such measurements. Second, in some embodiments, due to the additional mechanical constraint provided by the stabilization mechanism 610, the exemplary ligament balancing device 600 has improved stability (e.g., stiffness) characteristics, thereby eliminating (or at least attenuating) the effect of loading conditions on the measured gap and eliminating (or at least attenuating) the effect of central and lateral contact points on the measured gap. Third, in some embodiments, the stabilization feature 610 can be used to create a physical stop that limits the range of motion of the first plate 620, 630 relative to the second plate 640. Fourth, in some embodiments, by selecting the shape of the contact surface of the first plate 620, 630 (e.g., essentially concave on the medial side and substantially flat on the lateral side), the surgeon can perform accurate clearance capture throughout the full range of motion subject to femoral-tibial constraints intended to simulate the final implant shape. While the advantages of the device 600 have been described above with specific reference to the device 600 adapted for use in total knee replacement surgery, it will be apparent to those skilled in the art that similar advantages may be achieved through the use of the device 600 adapted for use in other types of joint surgery.

[0056] FIG. 7 illustrates a third exemplary ligament balancing device 700. In some embodiments, each elastic member or side of an elastic member may itself act as a stabilizing feature. Referring to the embodiment of FIG. 7, the elastic members feature a flexure that generates a substantially constant distraction force between the first and second plates throughout the range of motion of the first plate relative to the second plate, while functioning as a stabilizing feature. For example, the embodiment may feature a first set of springs 760 that compress axially (e.g., along an axis perpendicular to the bone-contacting surface of the second plate 750) and a second set of springs 770 that succumb to compression, where the first set of springs is not linearly aligned with the second set of springs. In some embodiments, the first set of springs 760 and the second set of springs 770 may be collectively referred to as an actuation mechanism, e.g., a mechanical actuation mechanism. In some embodiments, such an orientation results in generating an approximately constant force (e.g., within ±5% of the nominal force, or within ±10% of the nominal force, or within ±15% of the nominal force) between the first plate 710 or 720 and the second plate 750, regardless of the distance / height between them. As a result, the combination of at least two sets of springs functions as a force stabilization mechanism. Two such constant force embodiments featuring first plates 710, 720 and second plate 750 can be joined at the height of the second plate 750 to individually allow for simultaneous application of constant forces to the two sides of the bicondylar joint. For example, in an embodiment of device 700 adapted for use in a knee joint, the device may include a single second plate 750 adapted to interact with the patient's tibia and two first plates 710, 720, one adapted to interact with the medial condyle of the patient's femur and one adapted to interact with the lateral condyle of the patient's femur, both coupled to the same second plate 750.

[0057] As used herein, the terms "substantially constant distraction force" and "somewhat constant force" are used to describe the distraction force imparted by an exemplary ligament balancing device over the available range of motion of such ligament balancing device (e.g., from a fully compressed position to a fully extended position) and refer to a force that varies by only a certain percentage variance compared to a baseline distraction force (i.e., only a certain percentage greater or less than the baseline distraction force). For example, if the baseline distraction force of an exemplary ligament balancing device is ten (10) pounds and the certain percentage is 10%, then a "substantially constant distraction force" would be a force that is within plus or minus 10% of the baseline value of ten (10) pounds, i.e., between nine (9) pounds and eleven (11) pounds. In some embodiments, the percentage variance is 5%. In some embodiments, the percentage variance is 5% or less. In some embodiments, the percentage variance is 10%. In some embodiments, the percentage variance is 10% or less. In some embodiments, the percentage variance is 11%. In some embodiments, the percentage variance is 11% or less. In some embodiments, the percentage variance is 12%. In some embodiments, the percent variance is 12% or less. In some embodiments, the percent variance is 13%. In some embodiments, the percent variance is 13% or less. In some embodiments, the percent variance is 14%. In some embodiments, the percent variance is 14% or less. In some embodiments, the percent variance is 15%. In some embodiments, the percent variance is 15% or less. In some embodiments, the percent variance is 16%. In some embodiments, the percent variance is 16% or less. In some embodiments, the percent variance is 17%. In some embodiments, the percent variance is 17% or less. In some embodiments, the percent variance is 18%. In some embodiments, the percent variance is 18% or less. In some embodiments, the percent variance is 19%. In some embodiments, the percent variance is 19% or less. In some embodiments, the percent variance is 20%. In some embodiments, the percent variance is 20% or less.

[0058] FIG. 8 shows a rendering of a fourth exemplary ligament balancing device 800, derived from the third exemplary ligament balancing device 700. In the exemplary device 800, the elastic member has two series of springs 860, 870. In some embodiments, the series of springs 860, 870 may be collectively referred to as an actuation mechanism, e.g., a mechanical actuation mechanism. In some embodiments, the series of springs 860, 870 are stabilized, and force is applied to the tibial and femoral members via an internal piston 890, which prevents buckling in the case of compression springs. In some embodiments, the piston 890 is pivotally coupled to the tibial and femoral members (e.g., with a lubricated dowel) to reduce friction within this embodiment. In some embodiments, in addition to the stability created by the arrangement of the two series of springs 860, 870, a lateral stabilization mechanism 880 is provided to increase the stability of the first plate 810 and / or 820 relative to the second plate 850. In some embodiments, the spring series 860, 870 are positioned and aligned such that the applied force minimizes engagement of the lateral stability mechanisms, essentially reducing any frictional forces within the manifestation range.

[0059] 9A-9D illustrate how spring series 860, 870 cooperate to maintain a substantially constant axial distraction force between first plate 810 or 820 and second plate 850, regardless of the distance / height between first plate 810 or 820 and second plate 850. FIG. 9A illustrates the location of spring series 860, 870 within device 800. In some embodiments, spring series 860, 870 may be collectively referred to as an actuation mechanism, e.g., a mechanical actuation mechanism. As shown in FIG. 9A, spring series 860 may also be referred to as a diagonal spring, and spring series 870 may also be referred to as an axial spring. FIG. 9B illustrates the distraction force imparted by axial spring 870 along the range of motion of first plate 810 or 820. In some embodiments, the distraction force imparted by the axial spring 870, as measured along the axial axis of the device 800, directly correlates to Hooke's Law, such that the distraction force imparted by the axial spring 870 is directly (e.g., linearly) proportional to the displacement of the first plate 810 or 820 toward the second plate 850. FIG. 9C illustrates the distraction force imparted by the diagonal spring 860 in the axial direction along the range of motion of the first plate 810 or 820. In some embodiments, due to the orientation of the diagonal spring 860, the distraction force imparted axially by the diagonal spring 860 decreases as the first plate 810 or 820 approaches the second plate 850. This is because the length of the diagonal spring 860 decreases, thereby increasing the overall force imparted, while the change in orientation of the diagonal spring 860 as the first plate 810 or 820 approaches the second plate 850 causes a greater proportion of the overall force imparted by the diagonal spring 860 to be imparted laterally rather than axially. The combination of the axial force imparted by axial spring 870 and the axial force imparted by diagonal spring 860 results in a total axial distraction force imparted between first plate 810 or 820 and second plate 850. Figure 9D shows the total distraction force, which is the sum of the forces shown in Figures 9B and 9C.In some embodiments, the characteristics of each individual spring forming spring series 860, 860, as well as their number and orientation, are designed so that (1) the total axial distraction force is compatible with the desired use of device 800 (e.g., to provide an axial distraction force of 20 pounds per section for knee application or 40 pounds for shoulder application), and (2) the axial force imparted by axial springs 870 over the range of extension is substantially opposed to the axial force imparted by diagonal springs 860 over the range of stretch, thereby providing a substantially constant distraction force over the range of extension.

[0060] To illustrate how the diagonal springs 860 and axial springs 870 cooperate to provide a substantially constant distraction force, Figure 9E shows a side view of an exemplary device 800 including the diagonal springs 860 and axial springs 870. In Figure 9E, dimension a refers to the current longitudinal length of the diagonal springs 860, dimension b refers to the lateral distance between the pivot points of the two cooperating diagonal springs 860, and dimension c refers to the current length of the diagonal springs 860. The resultant force F imparted by the combination of the diagonal springs 860 and the axial springs 870 can be expressed as F = V + D, where V is the force imparted by the axial springs 870 and D is the force imparted axially by the diagonal springs 860. The force V can be calculated as V=kv*x*nv, where kv is the spring constant of the axial springs 870, x is the displacement of the axial springs 870 from their uncompressed state, and nv is the number of axial springs 870. In the embodiment shown in Figures 8 and 9A, there are two axial springs 870 for each of the first plates 810, 820, although this number may be different in other embodiments.

[0061] With continued reference to FIG. 9E, the force D is: TIFF0007738581000001.tif23150, where Ld is the free length of one of the cantilever springs 860, c0 is the length of one of the cantilever springs 860 when the device 800 is in an uncompressed state (e.g., fully extended), and cx is the length of the spring in the state at the point of interest (e.g., c1 refers to the length of one of the cantilever springs 860 when the device 800 is compressed by 1 mm, and c10 refers to the length of one of the cantilever springs 860 when the device 800 is compressed by 10 mm). where a is the length of one of the cantilever springs 860 (referring to the length of one of the cantilever springs 860), kd is the spring constant of the cantilever spring 860, ax is the vertical component of the cantilever spring 860 at a given point (e.g., a refers to the length of one of the vertical components of the cantilever spring 860 in the uncompressed device 800, and a refers to the length of one of the vertical components of the cantilever spring 860 when the device is compressed 10 mm), b is the lateral distance between the pivot points of two cooperating cantilever springs 860, and nd is the number of cantilever spring pairs. In the embodiment shown in Figures 8 and 9A, there are two pairs of cantilever springs 860 for each of the first plates 810, 820, although this quantity may be different in other embodiments.

[0062] 10A-10C show renderings of a ligament balancing device 1000 including side-specific modules 1001, 1002. In some embodiments, ligament balancing device 1000 is similar to one of ligament balancing devices 400, or 500, or 600, or 700, or 800, and is divided symmetrically at the level of the sagittal plane. In some embodiments, each side-specific module 1001, 1002 includes a first plate (e.g., a proximal femur plate) 1011, 1012, respectively, and a second plate (e.g., a distal tibia plate) 1051, 1052, respectively. In some embodiments, modules 1001, 1002 are coupled together using a mechanical connection (e.g., a dovetail mechanism, separate clips, etc.). In some embodiments, each of the modules 1001, 1002 may be used individually (e.g., in a partial knee), may be directly connected to one another but not to one another (e.g., in a cruciate-preserving bilateral or total knee), or may be both connected and connected to one another (e.g., in a total knee). In some embodiments, the modules 1001, 1002 are available in different configurations. In some embodiments, the ligament balancing device 1000 is provided as a kit (e.g., including modules 1001 and 1002), and the surgeon assembles the desired combination at the time of surgery. In some embodiments, the surgeon selects and obtains (e.g., orders) the appropriate element(s) of the ligament balancing device 1000 (e.g., selects module 1001, module 1002, or both) prior to surgery. In some embodiments, the selection of the appropriate element(s) of the ligament balancing device 1000 is based at least in part on preoperative imaging. In some embodiments, the selection of the appropriate element(s) of the ligament balancing device 1000 is coordinated with a pre-operative template that predefines both the appropriate element(s) of the ligament balancing device and the size of the implant(s) to be used.

[0063] In some embodiments, modules 1001, 1002 are available with different extension member stiffness levels (e.g., low, medium, or high distraction force). In such embodiments, the surgeon can select the appropriate stiffness level depending on the patient (e.g., high stiffness for high BMI patients or those needing more stability, low stiffness for low BMI patients). Furthermore, in such embodiments, the surgeon can leverage this selection to tailor stiffness depending on the compartment being considered, ensuring that the central collateral envelope is stiffer than the lateral collateral envelope structure. Thus, in such embodiments, the surgeon can use stiffer modules in the medial compartment than in the lateral compartment.

[0064] In some embodiments, the modules 1001, 1002 are available in different sizes in the lateral plane (e.g., small, large, etc.). In such embodiments, this selection may be advantageously utilized to better accommodate knee joint size, including when there is a substantial difference in size between the medial and lateral compartments. For example, such an embodiment may provide the surgeon with the option of using a smaller size (along the anterior-posterior axis) for the lateral compartment than for the medial compartment.

[0065] In some embodiments, the proximal side of the first plate of modules 1001, 1002 is available in different geometries (e.g., flat, concave, or convex). In some such embodiments, the proximal surface of the natural tibia is concave in the medial compartment and convex in the lateral compartment, allowing the surgeon to select the appropriate combination to replicate this natural characteristic.

[0066] FIG. 11 illustrates a fourth exemplary ligament balancing device 1100 that is a variation of the fourth exemplary ligament balancing device 800. In the embodiment illustrated in FIG. 11, the device 1100 includes a peripheral spring 1170 rather than the axial spring 870 illustrated in FIG. 8. In some embodiments, the peripheral spring 1170 is substantially contained within the periphery of the first plate 1110 or 1120. For example, in some embodiments, the peripheral spring 1170 is disposed entirely within the periphery of the first plate 1110 or 1120, and in some embodiments, the peripheral spring 1170 mimics (e.g., is coextensive with) the periphery of the first plate 1110 or 1120. In some embodiments, the device 1100 includes a diagonal spring 1160 that is substantially similar to the diagonal spring 860 illustrated in FIG. 8. In some embodiments, the diagonal spring 1160 and the peripheral spring 1170 can be collectively referred to as an actuation mechanism, e.g., a mechanical actuation mechanism. In some embodiments, the device 1100 includes a stabilization mechanism 1180 that is substantially similar to the stabilization mechanism 880 shown in Figure 8. In some embodiments, the use of a peripheral spring 1170 allows the stabilization mechanism 1180, configured to maintain the first plate 1110 or 1120 substantially parallel to the second plate 1150, to have an extended length, thereby increasing the extension range of the first plate 1110, 1120 relative to the second plate 1150.

[0067] 12A-12E illustrate a fifth exemplary ligament balancing device 1200. FIG. 12A illustrates a rendering of device 1200, and FIG. 12B illustrates an alternative rendering of device 1200 in which certain elements of device 1200 are rendered in a partially transparent manner to facilitate visibility of other elements of device 1200. In some embodiments, device 1200 includes two first plates 1210, 1220 and a second plate 1250. In some embodiments, the sixth exemplary ligament balancing device 1200 is similar to the fourth exemplary ligament balancing device 800 in that it maintains a substantially constant axial distraction force between the first plate 1210 or 1220 and the second plate 1250, regardless of the distance between the particular first plate 1210 or 1220 and the second plate 1250. In some embodiments, device 1200 uses a different exemplary mechanically actuated intra-articular mechanism than those described above. In some embodiments, device 1200 includes an elongated member 1230 that also functions as a stabilizing mechanism 1260. In some embodiments, device 1200 includes a leaf spring 1270. In other embodiments, device 1200 may include different types of springs. In some embodiments, stabilizing mechanism 1260 and leaf spring 1270 can be collectively referred to as an actuation mechanism, e.g., a mechanical actuation mechanism. In some embodiments, elongated member 1230 includes a pivot axis 1235, which creates a first moment arm between pivot axis 1235 and first plate 1210 or 1220 and a second moment arm between pivot axis 1235 and second plate 1250. In some embodiments, the extension member 1230 and leaf spring 1270 are designed such that changes in compression of the leaf spring 1270 due to movement of the first plate 1210, 1220 relative to the second plate 1250 are substantially compensated for by variations in the ratio between the first and second moment arms, so that the distraction force applied to the joint between the first plate 1210 or 1220 and the second plate 1250 remains substantially constant regardless of the distance between the first plate 1210 or 1220 and the second plate 1250.

[0068] 12C provides a more detailed view of the different moment arms present within device 1200 that result in the application of a substantially constant axial distraction force, as described above. As shown in FIG. 12C, the force applied to first plate 1210 or 1220 as a result of actuation of leaf spring 1270 is controlled by the moment arm of the force applied by leaf spring 1270 about the pivot point of telescoping member 1230 and the moment arm of the output force applied to first plate 1210 or 1220 about the pivot point of telescoping member 1230.

[0069] 12C, the first plate 1210 is placed in a compressed position relative to the second plate 1250, causing the leaf spring 1270 to exert a force of 56.25 lbs on the elastic member 1230 coupled to the first first plate 1210. In this position, the moment arm of the leaf spring 1270 is 0.144 inches, creating a moment about the pivot point of the elastic member 1230 of 56.25 lbs * 0.144 inches = 8.1 lb-inches. In this same position, the moment arm of the force exerted on the first first plate 1210 is 0.405 inches. In this position, the force exerted on the first first plate 1210 as a result of the moment calculated above is 8.1 lb-inches / 0.405 inches = 20 lbs.

[0070] In the same position of the device 1200 shown in FIG. 12C , the second first plate 1220 is positioned in an extended position relative to the second plate 1250, resulting in the leaf spring 1270 exerting a force of 29.02 lbs on the telescoping member 1230 coupled to the second first plate 1220. In this position, the moment arm of the leaf spring 1270 is 0.244 inches, causing a moment about the pivot point of the telescoping member 1230 of 29.02 lbs * 0.244 inches = 7.08 lb-inches. In this same position, the moment arm of the force exerted on the second first plate 1220 is 0.354 inches. In this position, the force exerted on the second first plate 1220 as a result of the moment calculated above is 7.08 lb-inches / 0.354 inches = 20 lbs.

[0071] In view of the above, it can therefore be seen that the leaf spring 1270 and the elastic member 1230 cooperate to provide a substantially constant distraction force to the first plate 1210 or 1220 at various points along the range of motion of the first plate 1210 or 1220. It will be apparent to one skilled in the art that the specific dimensions and force measurements provided above are exemplary only, and that the same principles can be embodied in larger or smaller devices configured to apply forces of greater or lesser magnitude, etc.

[0072] 12D-12F illustrate a fifth exemplary ligament balancing device 1200 variation configured to allow for intraoperative adjustment of the stiffness of the leaf springs 1270, thereby adjusting the distraction force applied by the device 1200. FIGS. 12D-12E illustrate a first variation of the device 1201, which is provided with a kit 1275 including at least two leaf springs 1270A, 1270B, etc. In some embodiments, each of the at least two leaf springs 1270A, 1270B, etc. has different mechanical properties (e.g., different cross-sections, different materials, different heat treatments, etc.) that combine to provide different stiffnesses for the at least two leaf springs 1270A, 1270B, etc. In some embodiments, the device 1201 is configured to allow for replacement of one leaf spring (e.g., leaf spring 1270A) with another leaf spring (e.g., leaf spring 1270B). In some embodiments, due to a stiffness difference between the two leaf springs in kit 1275, the distraction force applied by device 1201 varies depending on which particular one of the leaf springs in kit 1275 is used. For example, in some embodiments, kit 1275 includes a first leaf spring 1270A configured to apply a 15 pound distraction force to the joint via the device, a second leaf spring 1270B configured to apply a 20 pound distraction force to the joint via the device, a third leaf spring 1270C configured to apply a 25 pound distraction force to the joint via the device, and a fourth leaf spring 1270D configured to apply a 30 pound distraction force to the joint via the device. In some embodiments, the leaf springs in kit 1275 are most easily replaced when device 1201 is not placed in the patient's joint, so that when there is no compressive force from the joint, first plates 1210, 1220 are spaced apart from second plate 1250, thereby allowing easy access to one of the leaf springs in kit 1275 currently placed in device 1201.

[0073] 12F illustrates a second variation of device 1202. In the embodiment illustrated in FIG. 12F, device 1202 includes mechanism 1280 operable to increase or decrease the preload of leaf spring 1270, thereby increasing or decreasing the distraction force applied by device 1202. In some embodiments, mechanism 1280 includes a set screw. In other embodiments, mechanism 1280 includes an operable lever featuring a cam portion that contacts leaf spring 1270, which, depending on the section of the cam portion that contacts leaf spring 1270, increases or decreases the preload of leaf spring 1270, thereby increasing or decreasing the distraction force applied by device 1202. In some embodiments, adjustment of device 1202 can be performed in situ while device 1202 remains in place within the patient's joint. In use, the device 1202 allows the surgeon to adjust the distraction force based on patient characteristics (e.g., BMI, size, or ligament stiffness / condition) or based on the surgeon's preference in an attempt to personalize the distraction force (as input) based on the measured joint gap (as output).

[0074] In some embodiments, both device 1201 and device 1202 allow a user (e.g., a surgeon) to personalize the distraction force for each patient. In some embodiments, device 1201 and device 1202 can be adapted into compartment-specific versions similar to modules 1001, 1002 shown in FIG. 10A . In such embodiments, rather than providing modules 1001, 1002 with different stiffness levels (e.g., low, medium, high) to provide customization options for users, each compartment-specific device can be tuned to a unique distraction force at the time of surgery without the need for a kit. In some embodiments, such devices allow for fine tuning of the distraction force between the medial and lateral compartments and for different flexion angles (particularly for total knee arthroplasty, or more generally for any bicondylar joint), or for a given compartment and different flexion angles (e.g., for partial / hemi-knee arthroplasty or for unicondylar joint surgery). In some embodiments, device 1202 including adjustment mechanism 1280 allows for continuous adjustment of force throughout the available range rather than providing discrete incremental levels of distraction force (e.g., low, medium, high).

[0075] Both the fourth and fifth exemplary ligament balancing devices 1100, 1200 are presented herein as models of possible implementations. Based on these two descriptions, it will be apparent to those skilled in the art that the mechanical actuator of such a device can be understood in more general terms as a combination of two antagonistic submechanisms, i.e., submechanisms that provide axial biasing forces that vary in opposite directions relative to the direction of device movement. The two submechanisms are designed so that an increase in force induced by one of the submechanisms due to device movement is compensated for by a corresponding decrease in force induced by the other submechanism due to the same movement, thereby maintaining a substantially constant distraction force applied to the joint regardless of the distance between the opposing plates of the device. In some embodiments, the actuation mechanism is disposed between at least two plates intended to contact opposing bones of a given joint. As used herein, a "submechanism" should be broadly understood as a mechanism capable of absorbing, storing, and releasing energy through a change in geometry (e.g., a spring) or a change in a mechanical variable (e.g., a moment arm).

[0076] In some embodiments, the mechanical actuator is positioned within the perimeter defined by the first or second plate and the opposing bony structures of the joint, and the proposed device may be described as intra-articular and intracapsular. Intra-articular devices have advantages such as allowing for the arthrotomy of the joint to be closed to better reflect the physiological kinematics of the joint during manipulation, as well as allowing for a reduced footprint of the device.

[0077] While the exemplary embodiments described above incorporate compression springs and leaf springs, it will be apparent to one skilled in the art that the sub-mechanisms described herein may also be accomplished with any type of spring (e.g., compression springs, leaf springs, tension springs, torsion springs, disc springs, drawbar springs, spiral springs, garter springs, etc.) fabricated from a variety of materials (e.g., metals such as steel or aluminum, elastomeric materials, etc.) and configured in any shape and fit to achieve the intended distraction force.

[0078] In some embodiments, the exemplary ligament balancing device described above is configured for use in soft tissue management during total knee arthroplasty-type surgery. The device can be placed within the joint cavity of a prepared knee joint to apply similar distraction forces to both the lateral and medial compartments, allowing the surgeon to properly assess relative joint alignment as well as joint space under a consistent distraction force regardless of the joint gap / space of each compartment. In some embodiments, the versatility of the disclosed ligament balancing device allows such a device to be provided as part of a conventional mechanical instrument set or in combination with a navigation system. Similarly, in some embodiments, the exemplary balancing device described above can be used at different stages of a surgical procedure regardless of the surgical approach.

[0079] According to one example of usage, an exemplary ligament balancing device (e.g., device 400, 600, 700, 800, 1000, 1100, 1200, 1201, or 1202) is used in conjunction with a navigation system, such as the navigation system commercially available under the trade name EXACTECHGPS by Exactech, Inc. of Gainesville, Florida. In some embodiments, the navigation system includes an infrared charge-coupled device (CCD) camera and a display unit combined with a touchscreen tablet intended to be located in the sterile field (under sterile drapes) and directly accessible by the surgeon during surgery, and a tracker set configured to be rigidly coupled to the patient's bones. In some embodiments, the CCD camera is configured to define the 3D position and orientation of the tracker, surgical instruments, and system-specific probe within six degrees of freedom upon acquisition of anatomical landmarks. In some embodiments, the navigation system includes an intraoperative application configured to calculate the acquired data to establish a surgical plan and provide real-time visual guidance for executing the surgical plan. In some embodiments, the navigation system includes a navigated mechanical instrument intended to receive the tracker and facilitate the execution of the surgical plan.

[0080] In some embodiments, an exemplary ligament balancing device (e.g., device 400, 600, 700, 800, 1000, 1100, 1200, 1201, or 1202) is used in connection with a surgical approach known as "tibia first." FIG. 13A illustrates an exemplary ligament balancing device coupled to an exemplary compression handle 1300 for use in a tibia-first procedure. FIG. 13B illustrates the overall surgical workflow for a tibia-first procedure. In such a technique, a proximal tibial cut is made first, and potential osteophytes around the edges of the natural tibia and / or femur are removed. In some embodiments, the proximal tibial cut is performed to provide a joint space that is compatible with the overall dimensions of the exemplary ligament balancing device, both in terms of transverse dimension (defined more or less by the circumference of the proximal tibial cut) and thickness (defined by the distance between the proximal tibial cut surface and the native femur). Next, in some embodiments, the exemplary ligament balancing device is attached to the compression handle 1300 and compressed to minimize the overall thickness of the ligament balancing device (e.g., minimize the distance between the first and second plates), as shown in FIG. 13A. In some embodiments, once compressed, the exemplary ligament balancing device is placed into the joint space, and the compression handle is then removed from the ligament balancing device, resulting in the application of an axial distraction force to both the medial and lateral compartments of the joint (e.g., via the intermediate actuation mechanism located between the medial first and second plates that contact the medial condyle of the natural femur, and via the lateral actuation mechanism located between the lateral first and second plates that contact the lateral condyle of the natural femur).In some embodiments, at this stage, the surgeon can (1) balance the posterior knee in extension by extending the leg and recording the joint space in extension, and / or (2) balance the posterior knee in flexion by flexing the knee and recording the joint space in flexion, and / or (3) balance the posterior knee through an arc of motion by manipulating the leg from extension to flexion and recording the joint space from extension to flexion, and / or (4) balance the posterior knee through an arc of motion by manipulating the leg from flexion to extension and recording the joint space from flexion to extension. In some embodiments, for any of these options, the joint space at a particular flexion angle or over a range of flexion angles is recorded by the navigation platform as a tracking of the femoral reference (associated with the femur tracker) to the tibial reference (associated with the tibia tracker). In some embodiments, for options (3) and (4), several methods of handling the leg are possible, such as slowly moving the leg from extension to flexion or from flexion to extension, placing one hand on the posterior aspect of the femur with the tibia flexed to prevent the weight of the femur from affecting the measurements, and the other hand at the level of the distal tibia or heel, being careful not to impart varus / valgus or internal / external rotation moments to the knee joint. In some embodiments, based on the recorded joint space and other inputs (e.g., leg alignment, knee compartment size, alignment method), the navigation system calculates and displays a femoral plan including cutting parameters that the surgeon can verify immediately or fine-tune as needed. In some embodiments, once the femoral plan is confirmed, the femoral cut is performed under the guidance of the navigation system.

[0081] In some embodiments, a final optional step includes performing a trial reduction in which a trial femoral component is placed on the prepared femur and a ligament balancing device is placed twice into the joint space. In some embodiments, by maneuvering the leg through an arc of motion, this step provides the possibility to check joint clearance and alignment when axial distraction forces are applied to both the medial and lateral compartments in the same manner as described above.

[0082] In some embodiments, an exemplary ligament balancing device (e.g., device 400, 600, 700, 800, 1000, 1100, 1200, 1201, or 1202) is used in connection with a surgical procedure known as "modified gap balancing." FIG. 14A illustrates the overall surgical workflow for a "modified gap balancing" procedure. In some embodiments, in a "modified gap balancing" procedure, the distal femoral cut is made first, and the proximal tibial cut is made second. In some embodiments, in a "modified gap balancing" technique, the proximal tibial cut is made first, and the distal femoral cut is made second. In some embodiments, performing both cuts removes osteophytes around the edges of the natural tibia and / or femur to create a joint space that matches the overall dimensions of the ligament balancing device, both in terms of lateral dimension (generally defined by the circumference of the proximal tibial cut) and thickness (defined by the distance between the proximal tibial cut surface and the distal femoral cut surface). In some embodiments, the axial thickness of the ligament balancing device can be increased by spacer 1400 depending on the gap between the two bone cuts (see FIG. 14B). In some embodiments, spacer 1400 is positioned distally relative to the second plate. In some embodiments, spacer 1400 is positioned proximally relative to the proximal plate. In some embodiments, the ligament balancing device is attached to a compression handle and compressed to minimize the overall thickness of the ligament balancing device (e.g., a minimum distance between the proximal and distal plates). In some embodiments, once assembled with the compression handle (e.g., as shown above in FIG. 13A) and optionally one or more spacers described above, the compressed ligament balancing device is placed within the joint space while the joint is placed in extension, and then the compression handle is removed from the ligament balancing device. In some embodiments, such placement of the exemplary ligament balancing device results in the application of an axial distraction force to both the medial and lateral compartments of the knee joint.In some embodiments, at this stage, the surgeon evaluates the knee in extension by checking the overall leg alignment and the medial and lateral gap values ​​displayed on the navigation system screen. In some embodiments, based on this information, the surgeon may choose to perform ligament release to optimize alignment. In some embodiments, once proper balance in extension is achieved, the leg is flexed to assess balance in flexion. In some embodiments, because the proximal plate contacts the natural posterior condyles of the femur when the knee is flexed, it is necessary to remove spacer 1400 (if used to compensate for the thickness of the distal femoral cut) before balancing in flexion. At this stage, balancing can be performed (1) statically (e.g., at a defined angle related to the flexed leg, typically between 80° and 100° of flexion) or (2) dynamically by bringing the leg from mid- to high-flexion or high- to mid-flexion (required to ensure contact between the still-natural portion of the femur and the proximal plate). In some embodiments, the joint space at a particular flexion angle or over a range of flexion angles is recorded by the navigation platform by tracking a femoral reference (associated with the femur tracker) and a tibial reference (associated with the tibia tracker). In some embodiments, based on the recorded joint space and other inputs (e.g., knee component size, alignment method), the navigation system calculates and displays a femoral plan including cutting parameters for final femoral preparation, which the surgeon can then verify or fine-tune. In some embodiments, once the plan is confirmed, the final femoral cut is performed under the guidance of the navigation system.

[0083] In some embodiments, a final optional step includes performing a trial reduction in which a trial femoral component is placed on the prepared femur and a ligament balancing device is placed in the joint space, in some embodiments by maneuvering the leg through an arc of motion, which allows the surgeon to verify joint clearance and alignment when axial distraction forces are applied to both the medial and lateral compartments in the same manner described above.

[0084] In some embodiments, an exemplary ligament balancing device (e.g., device 400, 600, 700, 800, 1000, 1100, 1200, 1201, or 1202) is used in connection with a surgical procedure known as "femur first." FIG. 15 describes the overall surgical workflow for a "femur first" procedure. In some embodiments of a "femur first" procedure, all femoral cuts are made first (e.g., in contrast to the technique shown in FIG. 14, where only the distal femoral cut is made first), and the proximal tibial cuts are made next. In some embodiments of a "femur first" procedure, the proximal tibial cuts are made first, and all femoral cuts are made next. In some embodiments, following the making of all femoral and proximal tibial cuts, potential osteophytes around the edges of the natural tibia and / or femur are removed. In some embodiments, following removal of osteophytes, a trial femoral component is placed on the prepared femur, thereby creating a joint space that matches the overall dimensions of the exemplary ligament balancing device, both in terms of transverse dimension (generally defined by the circumference of the proximal tibial cut) and thickness (defined by the distance between the proximal tibial cut and the trial femoral component). In some embodiments, the ligament balancing device is then attached to the compression handle (e.g., as shown above in FIG. 13A ) and compressed to minimize the overall thickness of the ligament balancing device (e.g., minimum distance between the proximal and distal plates). In some embodiments, the compressed ligament balancing device is placed within the joint space, and the compression handle is then removed from the ligament balancing device, resulting in the application of axial distraction forces to both the medial and lateral compartments in the manner described above. In some embodiments, at this point, the surgeon checks the balance and alignment of the knee by maneuvering the leg through an arc of flexion and recording these data via a navigation system. In some embodiments, depending on the measured balance and alignment, the surgeon may or may not be satisfied. In some embodiments, once the surgeon is satisfied, the surgeon then implants the final implant component.In some embodiments, if the surgeon is not satisfied, the surgeon may choose to perform subsequent surgical modifications, such as ligament releases or bone cuts, to improve the balance and / or alignment of the knee joint, and then reassess the balance and alignment of the knee by maneuvering the leg through an arc of flexion after said surgical modifications.

[0085] In some embodiments, an exemplary ligament balancing device (e.g., device 400, 600, 700, 800, 1000, 1100, 1200, 1201, or 1202) is used in conjunction with conventional mechanical instrumentation (e.g., in the absence of a navigation system) as a balancer to assess symmetry of gaps (e.g., the difference between the medial and lateral gaps). In some embodiments, such assessment can be performed during any of the aforementioned surgical procedures.

[0086] Certain aspects of the exemplary embodiments described above with reference to Figures 4-15 have been described with particular reference to features of a knee joint. However, the principles embodied by the exemplary embodiments are also applicable to balance devices adapted for use with other joints.

[0087] FIG. 16 shows a perspective view of a device 1600 adapted for use in a total ankle arthroplasty. In some embodiments, the device 1600 includes a first plate (e.g., a proximal plate) 1310 configured (e.g., sized and shaped) to engage the distal end of the patient's tibia. In some embodiments, the first plate 1610 is configured to engage the distal cut surface of the patient's natural tibia. In some embodiments, the device 1600 includes a second plate (e.g., a distal plate) 1620 configured (e.g., sized and shaped) to engage the patient's natural talus. In some embodiments, the device 1600 includes a telescoping member 1630 disposed between the first plate 1610 and the second plate 1620 and operable to apply a distraction force between the first plate 1610 and the distal plate 1620, according to any of the exemplary embodiments described herein. In the embodiment shown in FIG. 16, the telescoping member 1630 includes a mechanical actuator (e.g., a structure including one or more springs). In some embodiments, the mechanical actuator is configured to provide a constant or somewhat constant force throughout the range of motion of the device 1600. In some embodiments, the device 1600 includes first and second stabilization mechanisms 1640, 1650 disposed between the first plate 1610 and the second plate 1620 and configured to provide enhanced stability (e.g., rigidity) to the device 1600 in a manner as described above. In some embodiments, the device 1600 includes one first plate 1610 and at least two second plates 1620. In some embodiments, the device includes at least two of the elastic members 1630, and each of the at least two second plates 1620 is associated with a corresponding one of the at least two elastic members 1630.

[0088] In some embodiments, the device 1600 is adapted for use in a total ankle arthroplasty process for repairing a patient's ankle joint, including the steps of: (1) cutting the distal end of the patient's natural tibia to create a cut tibial surface; (2) positioning the device 1600 between the cut tibial surface and the patient's natural talus; (3) moving the ankle joint through a range of motion while recording data characterizing the patient's ankle ligament laxity; and (4) planning the cut relative to the patient's talus and / or the release of surrounding soft tissue based on previously obtained patient's ankle ligament laxity, along with other factors such as the overall alignment of the ankle joint, the location and / or orientation of the cut relative to the talus based on anatomical or patient-specific considerations (e.g., the presence of a cyst near the ankle joint, the presence of a previously implanted surgical implant).

[0089] In some embodiments, the device 1600 is adapted for use in a total ankle arthroplasty process for repairing a patient's ankle joint, including the steps of: (1) cutting the proximal end of the patient's natural talus to create a cut talar surface; (2) positioning the device 1600 between the cut talar surface and the patient's natural tibia; (3) moving the ankle joint through a range of motion while recording data characterizing the patient's ankle ligament laxity; and (4) planning the cuts to the patient's tibia and / or the release of surrounding soft tissue based on previously obtained laxity of the patient's ankle ligaments, along with other factors such as the overall alignment of the ankle joint, the location and / or orientation of the cuts relative to the talus based on anatomical or patient-specific considerations (e.g., the presence of a cyst near the ankle joint, the presence of a previously implanted surgical implant).

[0090] FIGS. 17A and 17B show first and second perspective views of a device 1700 adapted for use in an anatomical total shoulder arthroplasty ("aTSA"). In the first perspective view of FIG. 17A, the device 1700 is shown in a collapsed position. In the second perspective view of FIG. 17B, the device 1700 is shown in an extended position. In FIGS. 17A and 17B, certain elements of the device 1700 are rendered in a partially transparent manner to enhance visibility of other elements of the device 1700. In some embodiments, the device 1700 includes a first plate (e.g., a medial plate) 1710 configured (e.g., sized and shaped, e.g., curved) to engage with a glenoid implant placed in the patient's natural glenoid or the patient's prepared glenoid. In some embodiments, the device 1700 includes a second plate (e.g., a lateral plate) 1720 configured (e.g., sized and shaped) to engage with the cut surface of the patient's proximal humerus and / or the surface of a prosthetic humerus. In some embodiments, the device 1700 includes a telescoping member 1730 disposed between the first plate 1710 and the second plate 1720 and operable to apply a distraction force between the first plate 1710 and the second plate 1720 according to any of the exemplary embodiments described herein. In some embodiments, such as shown in FIGS. 17A and 17B , the telescoping member 1730 is at least partially embedded within the first plate 1710. In the embodiment shown in FIGS. 17A and 17B , the telescoping member 1730 includes a mechanical actuator. In some embodiments, the telescoping member 1730 includes two antagonistic force sub-mechanisms 1760, 1770. In some embodiments, the device 1700 includes one or more stabilization mechanisms 1780 disposed between the first plate 1710 and the second plate 1720 and configured to provide enhanced stability (e.g., rigidity) to the device 1700 in a manner as described above. In some embodiments, the device 1700 is provided in an integrated arrangement in which the first plate 1710 is coupled to the second plate 1720 via subcomponents of the actuation mechanism (e.g., a combination of the elastic member 1730 and the stabilization mechanism 1780).As used herein, the term "integral" refers to an apparatus that is a single, unified, non-modular whole that is not configured to be adjusted with different interchangeable parts. In some such embodiments, the apparatus 1700 is provided as a kit including versions of the apparatus 1700 with different configurations of the size and shape of the first plate 1710. In some embodiments, the apparatus 1700 is provided as a modular apparatus with an interchangeable test element, the first plate 1710, including a telescoping sub-apparatus (e.g., including the telescoping member 1730 and the stabilization mechanism 1780) secured to the second plate 1720 (e.g., to fabricate a plate sub-assembly), and directly connectable to the telescoping sub-apparatus. In some such embodiments, the apparatus 1700 is provided as a kit including different configurations of the size and shape of the test element, the first plate 1710.

[0091] In some embodiments, device 1700 is adapted for use in an aTSA process for repairing a patient's shoulder joint, including the steps of: (1) cutting the proximal end of the patient's natural humerus to create a cut humeral surface; (2) placing a humeral component trial or implant on the cut humeral surface; (3) positioning device 1700 between the humeral component trial or implant and a natural or prepared glenoid portion of the patient's scapula; (4) moving the shoulder joint through a range of motion while recording data characterizing laxity of the patient's stifle ligament; and (5) (a) planning the preparation of the glenoid portion of the patient's natural scapula (if step 3 is performed on the natural glenoid portion of the patient's scapula) or (b) selecting a prosthetic joint based on the laxity of the patient's shoulder ligaments (if step 3 is performed on a prepared glenoid portion of the patient's scapula).

[0092] FIG. 18 shows a partially see-through perspective view of a device 1800 adapted for use in a reverse total shoulder arthroplasty ("rTSA"). In some embodiments, the device 1800 includes a first plate (e.g., a medial plate) 1810 configured (e.g., sized and shaped) to engage with a glenoid plate on the scapular side of a reverse shoulder prosthesis. In some embodiments, the device 1800 includes a second plate (e.g., a lateral plate) 1820 configured (e.g., sized and shaped) to engage with a humeral liner (or trial humeral liner) on the humeral side of the reverse shoulder prosthesis. It should be understood that the first and second plates 1810, 1820 are substantially similar to the various first and second plates described herein. In some embodiments, the device 1800 includes an elastic member 1830 positioned between the first plate 1810 and the second plate 1820 and operable to apply a distraction force between the first plate 1810 and the second plate 1820 according to any of the exemplary embodiments described herein. In some embodiments, such as the embodiment shown in FIG. 16 , the elastic member 1830 includes a mechanical actuator (e.g., an arrangement including one or more springs). In some embodiments, the mechanical actuator is configured to provide a constant or somewhat constant force throughout the range of motion of the device 1800. In some embodiments, such as the embodiment shown in FIG. 18 , the elastic member 1830 is at least partially embedded within the second plate 1820. In some embodiments, the device 1800 includes a stabilization mechanism 1840 positioned between the first plate 1810 and the second plate 1820 and configured to provide improved stability (e.g., rigidity) to the device 1800 in a manner as described above. Although only one stabilizing feature 1840 is visible in FIG. 16, in some embodiments, device 1800 includes more than one stabilizing feature of stabilizing feature 1840 (eg, two stabilizing features 1840).

[0093] In some embodiments, the device 1800 is provided as an integrated device in which the first plate 1810 is coupled to the second plate 1820 via a subcomponent of the actuation mechanism (e.g., the telescoping member 1830). In some such embodiments, the device 1800 is provided as part of a kit including different versions of the device 1800 having different configurations of the second plate 1820 in terms of size and shape. In some embodiments, the device 1800 is provided as a modular device including a tensioning subassembly secured to the first plate 1810 (e.g., to manufacture a plate subassembly) along with a second plate 1820 that is an interchangeable trialable element directly connectable to the tensioning subassembly. In some such embodiments, the device 1800 is provided as part of a kit including different versions of the second plate 1820 having different configurations of size and shape.

[0094] In some embodiments, device 1800 is adapted for use in an rTSA process for repairing a patient's shoulder joint, including the steps of: (1) preparing the patient's scapula and placing a glenoid plate on the patient's scapula; (2) preparing the patient's humerus and placing a humeral tray and a trial humeral liner on the patient's humerus; (3) positioning device 1800 between the glenoid plate and the trial humeral liner; (4) moving the shoulder joint through a range of motion while recording data characterizing the patient's shoulder ligament laxity; and (5) selecting a humeral liner and / or a humeral tray based on the patient's shoulder ligament laxity.

[0095] It will be apparent to those skilled in the art that aspects of the above-described embodiments can be combined with one another to allow a surgeon to personalize the ligament balancing device (e.g., a medial module with a high stiffness level, large size, and concave proximal femur plate coupled to an lateral module with a medium stiffness level, small size, and convex proximal femur plate) according to the needs of a given patient.

[0096] In some embodiments, the exemplary ligament balance device is configured to maintain a constant or quasi-constant distraction force without including or being coupled to any type of active control arrangement or mechanism. In some embodiments, the exemplary ligament balance device is configured to maintain a constant or quasi-constant distraction force without including or being coupled to any type of external control mechanism. In some embodiments, the exemplary ligament balance device is configured to maintain a constant or quasi-constant distraction force without being coupled to any type of external device. In some embodiments, the exemplary ligament balance device is a self-contained device configured to maintain a constant or quasi-constant distraction force without including or being coupled to any type of external control mechanism. In some embodiments, the exemplary ligament balance device is configured to maintain a constant or quasi-constant distraction force without including any type of powered (e.g., electrically operated) element. In some embodiments, the exemplary ligament balance device is configured (e.g., sized and shaped) to be positioned within the joint cavity and / or joint capsule of a joint (e.g., to be positioned entirely within the joint space such that tissue can close with the exemplary ligament balance device in place). In some embodiments, the exemplary ligament balancing device includes a mechanical actuation mechanism disposed entirely within the periphery of the first plate and the periphery of the second plate to enable the exemplary ligament balancing device to be positioned within the joint cavity and / or joint capsule of the joint.

[0097] In some embodiments, an exemplary ligament balancing device includes a motor (or motors) and transmission (or transmissions) used to control the extension of the elastic member. In some embodiments, feedback from a torque sensor enables a motor controller to adjust the motor output (e.g., speed, displacement, torque, or direction) to maintain a constant or quasi-constant force.

[0098] In some embodiments, an exemplary ligament balancing device includes a linear actuator (or actuators) that are used to control the extension of the elastic members. In some embodiments, feedback from a force sensor allows an actuator controller to adjust the actuator output (e.g., velocity, displacement, torque, or direction) while maintaining a constant or quasi-constant force.

[0099] In some embodiments, the elastic member comprises a thermo-mechanical actuator (e.g., shape memory alloy, thermal bimorph, heated spring, etc.) that is heated and cooled to maintain a constant or quasi-constant force.

[0100] In some embodiments, the magnetic field strength of the electromagnet is controlled to vary the interaction between the electromagnet and an opposing electromagnet or permanent magnet attached to the structure while maintaining a constant or somewhat constant force.

[0101] Test Results

[0102] The ligament balance device shown in Figures 8 and 9A was designed to apply a distraction force of 17.5 pounds per compartment (i.e., 35 pounds for both compartments). Five samples of such devices were prepared and tested as described herein. Each test sample was placed in a load frame, with the distal surface of the ligament balance device's distal plate (e.g., plate 2) positioned against a flat steel plate representing the proximal tibial cut, while the proximal surface of the proximal plate (e.g., plate 1) was in contact with the femoral component. Three different sizes of femoral component were tested. During testing, the gap was defined as the distance between the flat plate and the distal surface of the femoral component, and three gap values ​​were considered: 9 mm, 12 mm, and 15 mm. The resultant distraction force was measured via the load frame. Measurements were completed three times for each of the five sample ligament balancers, each tested against three sizes of femoral component at three different gaps. 19A and 19B show photographs of the test setup used to test the sample ligament balance device. FIG. 19C shows a table of the force measurements recorded during the above-described testing, demonstrating significant conformance to the intended distraction force (i.e., 34 pounds) and adequate repeatability. More specifically, the data shown in the table in FIG. 19C reflects a minimum recorded force of 32.1 pounds (i.e., across all five samples, all three femur sizes, all three gap distances, and all three test runs) and a maximum recorded force of 38.6 pounds (i.e., across all five samples, all three femur sizes, all three gap distances, and all three test runs). Thus, all recorded force values ​​(i.e., across all five samples, all three femur sizes, all three gap distances, and all three test runs) were within ±10.3% of the nominal design force.

[0103] While numerous embodiments of the present invention have been described, it is understood that these embodiments are merely exemplary and not limiting, and that numerous variations may be apparent to those skilled in the art. For example, all dimensions set forth herein are provided by way of example only and are for illustrative purposes and not intended to be limiting.

Claims

1. a first plate configured to interact with a first bony structure of the joint; a second plate configured to interact with a second bony structure of the joint opposite the first bony structure; at least one mechanical actuation mechanism disposed between the first plate and the second plate and configured to apply a distraction force along an axis between the first plate and the second plate to urge the first plate and the second plate apart; An apparatus comprising: The at least one mechanical actuation mechanism comprises: a first actuation sub-mechanism; a second operating sub-mechanism; It contains the first actuation sub-mechanism is configured to provide a first actuation sub-mechanism distraction force, and the second actuation sub-mechanism is configured to provide a second actuation sub-mechanism distraction force that opposes the first actuation sub-mechanism distraction force; the device is configured to have a range of extension ranging from a minimum distance between the first plate and the second plate to a maximum distance between the first plate and the second plate; the first actuation sub-mechanism distraction force varies as the device moves through the telescoping range from the maximum distance to the minimum distance; the second actuation sub-mechanism distraction force varies as the device moves through the telescoping range from the maximum distance to the minimum distance; Varying the first actuation sub-mechanism distraction force and varying the second actuation sub-mechanism distraction force combine to provide the distraction force that is a substantially constant distraction force throughout the telescoping range. Device.

2. the substantially constant distraction force is a distraction force that is within ±15% of a reference distraction force over the stretch range.

10. The apparatus of claim 1.

3. the substantially constant distraction force is a distraction force that is within ±10% of a reference distraction force over the stretch range.

3. The apparatus of claim 2.

4. the device is an integrated device; 10. The apparatus of claim 1.

5. the device is a modular device configured such that at least one of the first plate or the second plate is detachable from the at least one mechanical actuation mechanism; 10. The apparatus of claim 1.

6. The device is configured for use in a total knee replacement, a unilateral knee replacement, an anatomical shoulder replacement, a reverse shoulder replacement, a hip replacement, or an ankle replacement.

10. The apparatus of claim 1.

7. the first actuation sub-mechanism includes at least one axial compression spring oriented along the axis; the second actuation sub-mechanism includes at least one diagonal compression spring oriented diagonally relative to the axis; 10. The apparatus of claim 1.

8. the at least one diagonal compression spring is pivotally coupled to the first plate and the second plate; 8. The apparatus of claim 7.

9. the at least one axial compression spring is a peripheral spring disposed around an outer periphery of the second plate.

8. The apparatus of claim 7.

10. further comprising a stabilizing mechanism configured to maintain the first plate and the second plate substantially parallel to one another.

10. The apparatus of claim 1.

11. the joint is a bicondylar joint, the first plate is configured to interact with only a first condyle of the first bony structure of the joint.

10. The apparatus of claim 1.

12. a second first plate configured to interact with the first bony structure of the joint; a second mechanical actuation mechanism disposed between the second first plate and the second plate and configured to apply a second distraction force along an axis between the second first plate and the second plate to urge the second first plate and the second plate apart; and Furthermore, the device is configured to have a second telescopic range ranging from a minimum distance between the second first plate and the second plate to a maximum distance between the second first plate and the second plate; the second mechanical actuation mechanism is configured to provide a substantially constant distraction force across the second range of extension.

10. The apparatus of claim 1.

13. the second distraction force is different from the distraction force.

13. The apparatus of claim 12.

14. the mechanical actuation mechanism is at least partially embedded in one of the first plate or the second plate; 10. The apparatus of claim 1.

15. the device is sized to be placed within a joint space within the joint.

10. The apparatus of claim 1.

16. the mechanical actuation mechanism is disposed within an outer periphery of the first plate and within an outer periphery of the second plate.

10. The apparatus of claim 1.

17. A kit comprising a first device according to claim 1 and a second device according to claim 1.

18. 10. The substantially constant distraction force of the first device of claim 1 is greater than the substantially constant distraction force of the second device of claim 1.

18. The kit of claim 17.

19. The first device of claim 1 and the second device of claim 1 are configured to be coupled to each other at the second plates such that the axis of the distraction force of the first device of claim 1 and the axis of the distraction force of the second device of claim 1 are parallel to each other.

18. The kit of claim 17.

20. the first actuation sub-mechanism distraction force increases as the device moves through the telescoping range from the maximum distance to the minimum distance; the second actuation sub-mechanism distraction force decreases as the device moves through the telescoping range from the maximum distance to the minimum distance.

10. The apparatus of claim 1.

Images