Monocondylar tibial component

Abstract

In the present invention, a unicondylar tibial component is described. A first unicondylar component comprises a plate having a bearing surface and an opposing surface configured to be secured to a proximal end of a patient's tibia, the plate further comprising an anterior end, a lateral end, a posterior end and a medial end, the plate having a medial-lateral width W defined between the lateral end and the medial end, and a longitudinal anterior-posterior axis extending from the lateral end between the anterior end and the posterior end approximately one-third of the width of the plate (i.e., 1 / 3W) and defining a longitudinal axis length L of the plate. A first elongated peg projects from the opposing surface at the anterior portion and defines a first peg axis. A second elongated peg projects from the opposing surface at the anterior portion and defines a second peg axis. The first and second peg axes are disposed at an angle of 45-70° relative to the longitudinal anterior-posterior axis and are substantially parallel to one another such that the first and second pegs project posteriorly and distally relative to the plate. The anterior portion of the plate includes a portion defined by no more than the anterior 60% of the longitudinal axis length L of the plate, while the posterior portion of the plate includes a portion defined by no less than the posterior 40% of the remaining longitudinal axis length L of the plate, the posterior portion of the opposing surface being free of pegs or other fixation devices, and the first and second elongated pegs being disposed at a location more than half the medial-lateral width W of the plate from the periphery of the plate. The component is configured for cementless fixation using an interference fit. Also described are methods of installation and tools suitable for use in installation.

Description

Technical Field

[0001] The present invention relates to a unicondylar tibial component, and a method and apparatus for implanting the same. The present invention particularly relates to a unicondylar tibial component for cementless implantation, but is not exclusive.

Background Art

[0002] Knee arthroplasty typically involves a surgeon excising a patient's femur and / or tibia and implanting an artificial femoral component and / or an artificial tibial component into the excised bone to replace the joint surface. This surgery may be a total knee arthroplasty that replaces the joint surfaces of the femur and tibia (and optionally the patella), or a partial knee arthroplasty that replaces only a portion of the joint surface of the knee, such as a unicondylar knee arthroplasty (also called a unicondylar knee hemiarthroplasty).

[0003] The component to be implanted needs to be fixed to the excised bone by some means. For this reason, a tibial component often includes one or more anchors. The anchor may be located at the base or side of the component and is housed within a cavity formed in the patient's bone (e.g., obtained by drilling, carving, burring, or sawing) to assist in fixing the component in place. Such an anchor may be a keel, which is an elongated protrusion extending generally parallel to the anteroposterior axis of the component from the base of the component.

[0004] Bone cement can be used to fix implants (with or without anchors) in place. Bone cement is useful because it can fill the gap between the excised bone and the base of the implant. However, bone cement can deteriorate or crack over time, potentially causing implant loosening or damage and / or fragmentation within the knee compartment. Also, as bone is absorbed, the bond between the cement and the bone may break down. When a component loosens, it tends to sink. If a loose tibial component is subjected to uneven load distribution from the center, the tibial component may detach and sink. For example, knee flexion is known to cause implants on the tibial plateau to detach anteriorly, which can also lead to implant damage and / or fragmentation within the knee compartment.

[0005] Cementless fixation in unicompartmental knee arthroplasty, particularly medial unicompartmental knee arthroplasty, can sometimes offer better long-term outcomes than cemented fixation. Cementless components are designed to fix to the resected bone without the use of bone cement. Such components generally include a porous or microporous surface that promotes bone endografting into the component over time, which eventually forms a strong bond between the component and the patient's bone. To ensure the implant remains in place when bone endografting occurs, cementless components typically include one or more fixation mechanisms (e.g., keels) that are embedded in the patient's bone to form a press fit and / or tethered fit.

[0006] Cementless tibial fixation has two major early complications: tibial plateau fracture and insufficiency, which can lead to implant loosening or collapse and cause pain to the patient. Although these complications are rare, they are a significant problem for patients who experience them.

[0007] Tibial plateau fractures typically occur in the first few weeks after transplantation. This is likely because a crack may have formed during surgery and subsequently propagated through the stressed bone. In cementless fixation, fixation mechanisms such as keels are subjected to impact and press-fitting. This impact can cause cracks. Furthermore, the press-fitting can create stress within the bone, potentially leading to fracture propagation. Additionally, the use of longitudinal keels requires the formation of grooves within the bone, which can weaken the bone. During unicompartmental total knee arthroplasty, the superficial subchondral bone is removed. In a normal knee, this bone acts as a tension band that prevents the protruding medial condyle from fracturing. In a replaced knee, this tension band is removed, making it more susceptible to fracture.

[0008] Tibial component depression can take a long time to become apparent. During typical functional activity, the load on the tibial component is relatively concentrated when the knee is close to extension. As a result, the forces at the bone-implant (or bone-cement) interface located below the tibial component are primarily compressive, making it ideal for cementless fixation. Additionally, some shear forces are generated at the aforementioned interface due to the anterior-posterior movement of the femoral component during activity. These shear forces are relatively small (especially in the case of movable bearings, an order of magnitude smaller than the frictional force between the tibial component and bone). However, during high-load, high-flexion activities, the force is applied more posteriorly to the tibial component. This causes the bone to compress posteriorly, leading to a tendency for the anterior part of the component to lift away from the bone and for the component to tilt. Lateral radiographic images usually show a radiolucent area beneath the anterior surface of the cementless component, which is thought to be due to compromised fixation in this area, likely caused by the aforementioned detachment. When painful depression occurs, the bone collapses posteriorly, and the tilt of the component increases significantly. Such collapses are likely due to overloading of the posterior bone. Furthermore, collapses often result in valgus. This is probably because the component is better supported by the posteromedial cortex than the relatively flexible posterolateral cancellous bone, and / or because eccentric lateral loading occurs when the associated mobile bearing strikes the lateral wall of the component.

[0009] Generally, the more invasive the fixation method, the greater the likelihood of bone weakening and fracture. Furthermore, the forces involved in tightening and fitting the components can sometimes cause fractures. Conversely, the less invasive the fixation method, the lower the stability of the implant, making it more prone to loosening over time and potentially leading to bone depression and other complications.

[0010] Patent Document 1 recognizes the problem of the tibial component floating anteriorly and proposes an apparatus for unicompartmental knee arthroplasty. The apparatus includes a base plate having a first surface configured to be fixed to a surgically prepared medial (or lateral) compartment at the proximal end of the patient's tibia and a second opposite surface configured to mimic the medial (or lateral) tibial condyle, and a flange adjacent to the base plate and shaped to contact the surgically prepared anterior surface at the proximal end of the patient's tibia. The apparatus further includes at least one anchor protruding from the first surface and positioned to coincide with at least one corresponding surgically prepared cavity in the patient's tibia. The flange includes an opening through which the flange passes. This opening allows a fastening structure in the form of a rod to pass through the flange and be introduced through the patient's tibia toward a posterior receptacle on the first surface. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] U.S. Patent Application Publication No. 2012 / 330431 [Overview of the project] [Means for solving the problem]

[0012] According to a first aspect of the present invention, a unicondylar tibial component is a plate having a support surface and an opposing surface configured to be fixed to the proximal end of a patient's tibia, wherein the plate further comprises an anterior end, a lateral end, a posterior end and a medial end, the width W of the plate in the inward-outward direction is defined between the lateral end and the medial end, the longitudinal anterior-posterior axis extends from the lateral end between the anterior end and the posterior end by about one-third (i.e., 1 / 3W) of the width of the plate, and defines the longitudinal axis length L of the plate. A unicondylar tibial component is provided, comprising: a tibial base; a first elongated peg protruding from the opposing surface in its anterior portion and defining a first peg axis; and a second elongated peg protruding from the opposing surface in its anterior portion and defining a second peg axis, wherein the first and second peg axes are positioned at an angle with respect to the longitudinal anterior-posterior axis and are substantially parallel to each other; and no pegs or other fastening devices are positioned on the posterior portion of the opposing surface; and the component is configured for cementless fixation using a compression fit.

[0013] The absence of pegs or other fixation devices (such as keels) on the posterior portion of the component allows for placement in a manner that reduces trauma to the posterior portion of the patient's tibia. The angled nature of parallel pegs resists peg dislodgement after placement. In particular, angled pegs prevent the anterior portion of the component from lifting (when a load is applied posteriorly, the component cannot move forward, causing it to be pulled straight out). Components possessing these features are less likely to cause tibial fractures or loosening of the component after cementless fixation.

[0014] As used herein, cementless fixation refers to a method of attaching components without using bone cement. Therefore, components suitable for cementless fixation are those that can be attached to and fixed to the patient's bone without using bone cement. The components described herein are suitable for cementless fixation because the pegs are shaped to form a suitable-sized hole and interlocking fit in the patient's tibia. The components described herein do not require any primary fixation other than the interlocking fit by the pegs, and therefore no other primary fixation mechanisms are provided. The components may further include surface structures or treatments on one or more of their bone contact surfaces that promote bone ingrafting into those surfaces and promote secondary fixation over time.

[0015] As described herein, the front portion of a plate is defined as the portion including 60% or less (e.g., 55% or 50%) of the front (front portion) of the longitudinal front-rear axis of the plate. The rear portion is defined as the portion including 40% or more (e.g., 45% to 50%) of the remaining portion of the plate, i.e., the rear (rear portion) of the longitudinal axis. The longitudinal front-rear axis is located approximately one-third of the width of the plate from the inner edge of the plate, and may be substantially located where a keel is present, if any.

[0016] The first and second peg axes may be positioned at angles of 45–70°, 55–65°, or approximately 60° with respect to the longitudinal anterior-posterior axis. Such inclined angled pegs may be configured to prevent the component from floating vertically away from the patient's bone after implantation. The first and second pegs may be angled toward the rear of the plate; that is, the tip of each of the first and second pegs is located further rearward than the base of the same peg. Alternatively, the pegs may be angled at a 90° angle to the opposite side; that is, the pegs may be angled only in the anterior-posterior direction and not in the inward-outward direction.

[0017] One or more of the elongated pegs may have a high aspect ratio, for example, a length-to-width ratio of 3:2, 2:1, 3:1, or higher. In addition to the high aspect ratio, each peg may have a length of 6–12 mm (e.g., 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, or 12 mm) and a maximum diameter of 4–8 mm (e.g., 4 mm, 5 mm, 6 mm, 7 mm, or 8 mm). Such high-aspect-ratio pegs reduce trauma to the tibia and further reduce the risk of the component being pulled vertically from the bone.

[0018] One or more cross-sections of the elongated pegs may be elliptical. One or more elongated pegs may be tapered. One or more elongated pegs may include a round or tapered tip.

[0019] The pegs may be arranged in a front-to-back direction, that is, the first peg may be positioned in front of the second peg. The pegs may be aligned in a straight line with each other (i.e., they may be located in the same front-to-back plane). The plate may include a front-to-back axis length, which can be defined as the longitudinal front-to-back axis length. The first elongated peg (more specifically, the base of the peg where the peg axis intersects the front-to-back axis) is positioned at a position one-fifth of the front-to-back axis length from the front end of the axis, and the second elongated peg is positioned at a position half the front-to-back axis length from the front end of the axis.

[0020] The plate may include a width in the medial-lateral direction, which can be defined as the width of the widest part of the plate between the medial side of the plate (i.e., the side intended to be positioned closest to the tibial tuberosity) and the lateral side of the plate (i.e., the side intended to be positioned away from the tibial tuberosity). Both pegs may be positioned beyond one-third of the plate's width from the outside of the plate, for example, beyond half of the plate's width from the outside of the plate, or between one-half and three-quarters of the plate's width from the outside of the plate.

[0021] One or more of the elongated pegs may contain one or more barbs.

[0022] The components may each include a cementless fixing coating on each of the elongated pegs, and the coating may not be present in one area of each peg, whereby each of the above areas has a diameter narrower than the maximum diameter of the coated peg. The coating may not be present in the base area of each peg adjacent to the opposing surface, whereby each of the above base areas has a diameter narrower than the maximum diameter of the coated peg.

[0023] One or more of the elongated pegs may include an area narrower than the maximum diameter of the peg.

[0024] According to a second aspect of the present invention, there is provided a guide tool for unicondylar knee arthroplasty, comprising a guide plate shaped to mimic a plate of a tibial component having a longitudinal anteroposterior axis, a first drill guide configured to guide a drill through the guide plate along a first drill axis, and a second drill guide configured to guide a drill through the guide plate along a second drill axis, wherein the first and second drill axes are arranged at an angle with respect to the longitudinal anteroposterior axis and are substantially parallel to each other.

[0025] The angle may be in the range of 45 - 70°, for example 55 - 65° or about 60°.

[0026] The guide plate may include a length in the anteroposterior direction. The first drill guide may be disposed at a position one-fifth of the length from the front end of the guide plate, and the second drill guide may be disposed at a position half of the length from the front end of the guide plate.

[0027] The guide tool may further include a drill stop operable to interact with the drill to prevent drilling a hole beyond a predetermined depth by the first or second drill guide.

[0028] The guide device may further include a clamp that is operable to engage between the guide plate and the patient's femur.

[0029] A third aspect of the present invention provides a kit comprising one or more tibial components according to a first aspect of the present invention and a guide according to a second aspect of the present invention. The first drill guide may have, for example, a shape having a maximum inner diameter, the size of which is determined such that the maximum diameter of the hole drilled through the first drill guide is smaller than the maximum diameter of the first peg. Similarly, the second drill guide may have, for example, a shape having a maximum inner diameter, the size of which is determined such that the maximum diameter of the hole drilled through the second drill guide is smaller than the maximum diameter of the second peg. The drill diameter may be, for example, 0.25 mm, 0.5 mm, 0.75 mm, or 1 mm smaller than the diameter of the corresponding peg.

[0030] A fourth aspect of the present invention provides a method for attaching a unicondylar tibial component, comprising the steps of: excising the surface of the tibia of a patient to whom the tibial component is to be attached; fixing a guide device according to one embodiment described herein to the excised tibia surface; drilling a first oblique peg hole in the excised tibia using a first drill guide of the guide device; drilling a second oblique peg hole in the excised tibia using a second drill guide of the guide device, wherein the second peg hole is parallel to the first peg hole; and inserting a unicondylar tibial component according to one embodiment described herein into the excised and drilled tibia.

[0031] The maximum diameter of the first angled peg hole may be smaller than the maximum diameter of the first peg. Similarly, the maximum diameter of the second angled peg hole may be smaller than the maximum diameter of the second peg. The drill diameter may be, for example, 0.25 mm, 0.5 mm, 0.75 mm, or 1 mm smaller than the diameter of the corresponding peg.

[0032] According to a fifth aspect of the present invention, a unicondylar tibial component is provided, comprising a plate having a support surface and an opposing surface configured to be fixed to the proximal end of the patient's tibia, and a keel protruding from the opposing surface, wherein the plate comprises an anterior portion, a posterior portion, and a longitudinal anterior-posterior axis having an anterior-posterior axis length, in this embodiment, the anterior portion comprises 76% or less of the longitudinal anterior-posterior axis length, the posterior portion comprises the remaining 24% or more of the longitudinal anterior-posterior axis length, the keel is located on the anterior-posterior axis and protrudes from the opposing surface in the anterior portion, no fixing device such as the keel is provided in the posterior portion of the opposing surface, and the component is configured for cementless fixation using a compression fit.

[0033] A typical conventional keel has a length of approximately 60% or less of the longitudinal axis length, depending on the size of the component. Such a keel is usually located in the center of the longitudinal axis. For example, if the keel length is 58% of the longitudinal axis, the keel will not be included in the front 21% of the opposing surface, nor in the rear 21% of the opposing surface.

[0034] However, in the case of the tibial component according to the fifth aspect of the present invention, since the keel is located anterior to the plate compared to a conventional keel, damage to the posterior portion of the tibia during implantation is reduced.

[0035] The keel may include a leading edge and a trailing edge. The leading edge is positioned less than 20% of the longitudinal axis length from the front rim of the plate (e.g., 19%, 18%, 17.5%, 17%, or less), and the trailing edge is positioned more than 23% of the longitudinal axis length from the rear rim of the plate (e.g., 24%, 24.5%, 25%, 26%, or more).

[0036] In conventional keels, the distance d1 between the leading edge and the front rim may be equal to the distance d2 between the trailing edge and the rear rim. In contrast, in the keel described herein, the distance d3 between the leading edge and the front rim may be less than the distance d4 between the trailing edge and the rear rim. For example, distance d3 may be 80% or less of distance d4, for example, 75%, 74%, 73%, 72%, 71%, or 70%.

[0037] According to a sixth aspect of the present invention, a unicondylar tibial component is provided, comprising a plate having a support surface and an opposing surface configured to be fixed to the proximal end of the patient's tibia, and a keel protruding from the opposing surface, wherein the component is configured for cementless fixation using a compression fit, and the keel comprises a base adjacent to the opposing surface, a tip distal to the opposing surface, and medial and lateral walls, the medial and lateral walls tapering inward from the base to the tip.

[0038] In other words, the keel narrows (i.e., becomes thinner) towards the tip compared to its width at the base adjacent to the opposing surface. This tapering keel provides a tighter fit to the tibia, reducing the likelihood of loosening over time.

[0039] The taper angle may be in the range of 0.5 to 4°, for example, 1°, 2°, or 3°.

[0040] A seventh aspect of the present invention provides a unicondylar tibial component comprising a plate having a support surface and an opposing surface configured to be fixed to the proximal end of a patient's tibia, and a fixation mechanism protruding from the opposing surface, wherein the component is configured for cementless fixation using a quill fit, the component has a cementless fixation surface and / or coating on the opposing surface, and at least a portion of the fixation mechanism has a smooth outer surface.

[0041] The fixing mechanism may be a keel or peg, for example, an angled peg as described above.

[0042] In cementless fixation, the opposing surfaces and fixation mechanisms typically include surface structures or treatments that promote bone endografting to the surface, thereby facilitating secondary fixation over time. Rough surfaces, such as those designed for bone endografting, have been found to act as a file when inserting cementless components into the prepared tibia. This can potentially widen the prepared hole or groove in the tibia, reducing the integrity of the interlocking fit.

[0043] In a seventh embodiment of the present invention, such surface structures or treatments may not be partially or completely present on the fastening mechanism. Alternatively, the reabsorbable coating may be provided on part or all of the fastening mechanism so as to partially or completely cover any roughened treatments or coatings present on the fastening mechanism.

[0044] The insertion surface of the fixation mechanism may be smooth (e.g., it may have no cementless fixation surface and / or coating, or may be covered with a reabsorbable coating). In this specification, “insertion surface” refers to the surface of the fixation mechanism that is operable to be initially inserted into the bone cavity in order to guide the rest of the fixation mechanism. If such an insertion surface is rough, its abrasive effect will be significantly greater than any abrasive effect from the rest of the fixation mechanism. Therefore, by providing a smooth insertion surface, the abrasive effect described above can be significantly reduced. The rest of the fixation mechanism may be provided with (uncovered) surface structures or treatments that promote bone endografting and still maintain a large covering surface area for bone endografting.

[0045] In the case of pegs, the insertion surface may include the tip of the peg. The tip of the peg may be smooth, round, or spherical. The shaft of the peg may be provided with a cementless fixing surface and / or a coating. For example, since the maximum diameter of the tip of the peg may be wider than the maximum diameter of the shaft of the peg, a pocket may be provided between the tip of the peg and the opposing surface, thereby allowing a porous coating to be applied to the shaft of the peg between the tip and the opposing surface. The depth of the pocket can be selected so that the coating applied within the pocket does not protrude beyond the maximum diameter of the tip of the peg.

[0046] In the case of a keel, the insertion surface may include all or part of the rear edge of the keel and all or part of the lower edge of the keel. The insertion surface may further include all or part of the front edge of the keel. Therefore, the outer rim or part of the keel may be smooth. The cementless fixing surface and / or coating may be provided on parts of the keel other than the insertion surface. For example, a porous coating may be applied between the smooth outer rim and the opposing surface. A recess or pocket may be provided between the insertion surface and the opposing surface of the keel, thereby allowing a porous coating to be provided in the pocket. The depth of the pocket can be selected so that the coating applied in the pocket does not protrude beyond the outer rim in the inward and outward directions.

[0047] The entire outer surface of the fixing mechanism may be smooth. In other words, the fixing mechanism may not have a cementless fixing surface and / or coating.

[0048] The fixation mechanism may be provided with surface structures or treatment areas that promote bone endografting on all external surfaces, and such structures or treatment areas are covered with an absorbable coating, either fully or partially (for example, only on the insertion surface, as described above) to provide a smooth surface at the time of implantation. An example of a suitable reabsorbable material is calcium paste.

[0049] Features of each aspect of the present invention may be combined with features from other aspects of the present invention as needed, or with features obtained from the following description. [Brief explanation of the drawing]

[0050] Please refer to the attached drawings below, but these are for illustrative purposes only.

[0051] [Figure 1] A perspective view of the lower part of the tibial component is shown. [Figure 2] Figure 1 shows a lateral view of the tibial component. [Figure 3] Figure 1 shows a plan view of the lower side of the tibial component. [Figure 4] Figure 1 shows an anterior view of the tibial component. [Figure 5a] A lateral view of the alternative tibial component is shown. [Figure 5b] A lateral view of the alternative tibial component is shown. [Figure 5c] A lateral view of the alternative tibial component is shown. [Figure 5d] A lateral view of the alternative tibial component is shown. [Figure 5e] A lateral view of the alternative tibial component is shown. [Figure 6] A schematic anterior view of the tibial component in Figure 1 after it has been transplanted to the tibia is shown. [Figure 7] A schematic lateral view of the tibial component is shown in Figure 6. [Figure 8] This diagram shows a drill guide used in the transplantation method. [Figure 9] This diagram shows the transplantation method. [Figure 10] This figure schematically illustrates the use of the drill guide shown in Figure 8 during the process shown in Figure 9. [Figure 11] This figure schematically illustrates the use of the drill guide shown in Figure 8 in a process following the method step shown in Figure 9. [Figure 12]For comparison, this figure shows a conventional size A tibial component with a keel positioned in the central part. [Figure 13] This figure shows a tibial component of size A with an anterior keel. [Figure 14] This figure shows a size A tibial component with a tapered central keel. [Figure 15] This figure shows a size A tibial component with a tapered anterior keel. [Figure 16] For comparison, this figure shows a conventional size G tibial component with a centrally located keel. [Figure 17] This figure shows a tibial component of size G with an anterior keel. [Figure 18] This figure shows a tibial component of size G with a tapered central keel. [Figure 19] This figure shows a tibial component of size G with a tapered anterior keel. [Figure 20] This diagram schematically shows a tibial component including a keel with a smooth outer rim. [Figure 21] This figure shows a keel and peg similar to the keel shown in Figure 20. [Modes for carrying out the invention]

[0052] As mentioned above, cementless fixation has two major early complications: tibial plateau fracture and loosening, and painful tibial component depression. Factors contributing to these complications include: a) movement at the interface between the component and bone due to the load on the tibial component, b) weakening of the bone during component placement, and c) the force generated within the bone by fixing the component by interlocking, which can cause the bone to crack. Such complications may be more common in smaller patients (e.g., those under 5 feet 4 inches tall). Considering these patients, the fixation mechanisms (including multiple mechanisms) provided for the tibial component tend to be relatively larger compared to the patient's bone size than in larger patients. Therefore, smaller patients may require relatively more bone removal than larger patients, resulting in relatively weaker remaining bone that is more prone to fracture and depression.

[0053] Figures 1-4 show a tibial component 10 for unicompartmental knee arthroplasty. This component may be used in the medial or lateral compartment of the patient's knee. In the illustrated example, the component is shaped to fit the medial compartment. Figures 1 and 3 show a component with a bone-component interface at the top. Figures 2 and 4 show a component with a support surface 18 at the top.

[0054] The tibial component 10 includes a plate 12 and at least one elongated peg. In the illustrated example, two elongated pegs are shown: a first peg 14 and a second peg 16. It should be understood that more elongated pegs, e.g., three, four, five, or more, can be provided as needed.

[0055] Plate 12 is configured to replace the articular surface of the patient's tibia, in this case the medial tibial support surface. The plate includes a support surface 18 that replaces the patient's tibial support surface when fitted. Thus, the support surface 18 is shaped to work either directly with the patient's femur (or femoral replacement component) or with a support component positioned between the tibial component and the femur / femoral replacement component.

[0056] In the illustrated example, plate 12 is substantially flat and has a contour shaped to mimic the natural shape of the patient's tibia. Since the illustrated example is a medial tibial component, this plate is formed in a roughly C-shape on the medial side and includes an upright wall or lip 20 on the opposing lateral side, the upright wall or lip 20 intended to abut against the central tibial tuberosity of the patient's tibia when the component is fitted. The lateral tibial component is a mirror image of the illustrated component. It should be understood that this plate may have a different shape, for example, it may be roughly circular or elliptical.

[0057] The opposing surface 22 of the plate is configured to be fixed to the proximal end of the patient's tibia, as detailed below.

[0058] The plate 12 has a front end 24, an inner part 25, a rear end 26, and an outer part 27. The width W of the plate in the inward and outward directions is defined between the inner and outer parts, and the longitudinal front-to-rear axis 28 extends from the outer part between the front and rear parts by about one-third of the width of the plate (i.e., 1 / 3W), defining the longitudinal axis length L of the plate. It will be understood that the longitudinal front-to-rear axis 28 is usually located in the plane of the plate. Therefore, if the opposing surfaces are flat, the longitudinal front-to-rear axis 28 is usually located in the plane of the opposing surface 22.

[0059] Primary fixation is essential for maintaining the component in a stationary state after transplantation, allowing bone to grow within the implant and anchor to it, thereby achieving secondary fixation. As mentioned above, the common loosening mechanism is posterior depression / anterior detachment, requiring the anterior portion of the component to be held in place. The inventors have found that to minimize the risk of bone depression in the posterior tibia, it is better to leave the posterior tibial surface as intact as possible and avoid drilling fixation holes.

[0060] Therefore, it is useful to include a virtual line 30 that divides the plate 12 into a front portion 29 and a rear portion 31 along the inward-outward direction. In the illustrated example, the front portion includes the portion defined by the front 50% of the longitudinal axis length L of the plate (also referred to herein as the front 50% of the plate), while the rear portion includes the portion defined by the rear 50% of the longitudinal axis length L of the plate (i.e., the remainder of the plate, also referred to herein as the rear 50% of the plate).

[0061] Therefore, in the illustrated example, line 30 bisects the longitudinal axis 28. It should be understood that the dividing line 30 may divide the longitudinal axis in a different way; for example, the front portion may be 60% of the front of the plate, and the rear portion may be 40% of the remaining (rear) portion of the plate. The ratio of the front portion to the rear portion of the plate may be 60:40 or less, for example, 55:45 or 50:50. Thus, as described above, the rear portion includes at least 40% of the plate, as defined according to the longitudinal axis length.

[0062] The plate 12 includes at least one elongated peg 14, 16 protruding from the opposing surface 22 in the front portion 29 of the component. The rear portion 31 of the component does not have any pegs or other fastening mechanisms. More specifically, the base(s) of the elongated peg(s) are located in the front portion rather than the rear portion (because at least the rearmost axis of the peg may extend beyond the imaginary dividing line 30). The component does not include a keel and does not include any additional primary fastening mechanisms other than the pegs 14, 16.

[0063] The pegs 14 and 16 are configured to hold the component in a stationary position, allowing bone to grow within the component over time. Specifically, the pegs 14 and 16 are configured to form a crimp or press fit with holes drilled in the patient's tibia.

[0064] In the illustrated example, plate 12 includes two pegs: a first elongated peg 14 and a second elongated peg 16. Both pegs 14 and 16 are positioned on the anterior portion 29 of the plate. In the illustrated example, the first elongated peg is positioned at a distance between the second peg 16 and the anterior end portion 24 of the plate. However, it should be understood that other peg configurations are possible. For example, both pegs may be positioned at the same longitudinal position and spaced apart along the medial-outer direction, or they may be positioned at different longitudinal and medial-outer positions with spacing between them. However, in any configuration, no pegs (or other fastening mechanisms) are positioned on the posterior portion 31 of the plate. Furthermore, to avoid weakening of shallow bone in the area adjacent to the outer edge (in this case, the medial edge) of the plate, no pegs are positioned in that area. In the illustrated example, no pegs are positioned on the outer two-thirds (i.e., 2 / 3W) of the plate. In other examples, pegs may not be positioned in the outer half or outer third of the board.

[0065] In the illustrated example, the second peg 16 is substantially positioned on the dividing line 30, so that the dividing line 30 penetrates the base of the peg. Thus, one possible configuration is to position the first peg 14 at approximately one-fifth (20%) of the longitudinal axis length and the second elongated peg at approximately half the longitudinal axis length.

[0066] The first elongated peg 14 defines the first peg axis 32 (i.e., the longitudinal axis of the peg itself), and the second elongated peg defines the second peg axis 34. Both peg axes are positioned at an angle of 36° with respect to the longitudinal front-to-back axis of the plate. The “angle” used in the above description means an acute angle significantly smaller than 90°, so that the peg is oblique to the plate and extends rearward and distally relative to the plate. The above angle may be in the range of 45 to 70°, for example, in the range of 55 to 65°, and in the illustrated example, it is approximately 60°. Both pegs are positioned at the same angle so that they are substantially parallel to each other. It will be understood that the “angle” here refers to the angle in the front-to-back direction. That is, the pegs are not angled in the inward or outward direction.

[0067] It was found that, because no pegs or other fastening devices are positioned on the opposing surface 22 of the plate behind the second elongated peg 16, trauma to the posterior portion of the bone during implantation is minimized as much as possible.

[0068] When a cementless component is sufficiently loosened, it can be pulled out of the bone to which it is attached. However, such a component can only be pulled out of the bone in a direction parallel to the fixation peg, except in the case of a fracture. The oblique nature of the anterior pegs 14, 16 ensures that the pegs are configured to resist the component being pulled out perpendicularly from the bone, thereby resisting the anterior portion of the component lifting when a posterior load is applied with the knee flexed.

[0069] The parallel nature of the peg makes this component ideal for cementless fixation. This is because the component can be pressed into place and form an interlocking fit in a properly drilled hole located on the surface of the excised tibia. To ensure a secure interlocking fit, the diameter of the drilled hole must be narrower than the diameter of the peg intended to be fitted, for example, 0.5 mm or 1 mm narrower.

[0070] In the illustrated example, both pegs are positioned side by side (i.e., along an axis parallel to the longitudinal axis). They are positioned on the inside (in this case, outside) of the plate (i.e., closer to the lip 20 than the curved outer edge, and in this example, approximately one-third the width of the plate from the lip, and substantially along the longitudinal axis 28). This ensures that the pegs are configured to be mounted in deeper bone, closer to the center of the tibia, rather than in bone that protrudes toward the edge of the surface-reconstructed compartment.

[0071] One or more elongated pegs, in this case pegs 14 and 16, both have a high aspect ratio; that is, the peg is narrower than it is long. The length-to-width ratio may be 3:2, 2:1, or any other. This high aspect ratio allows the peg to penetrate deeply into the bone, preventing the bone above the lower part of the peg from lifting or breaking. When using thin pegs, there is little need to remove bone in the upper part of the tibia, leaving a large amount of bone to transmit tension and prevent fracture. A sufficiently high aspect ratio can be obtained with pegs having a length of 6-12 mm and a maximum diameter of 4-8 mm. In the illustrated example, the peg is approximately 9 mm long and has a maximum diameter of 5 mm. Pegs for cemented implants usually have a very low aspect ratio, often with width equal to length. This necessitates the formation of a larger cavity within the bone, weakening the patient's tibia.

[0072] One or more cross-sections of the elongated pegs, in this case both pegs 14 and 16, may be elliptical. In particular, the pegs may be narrower in the anterior-posterior direction than in the medial-lateral direction. This further reduces the amount of bone that needs to be removed from the tibia to securely fix the component. Also, wider dimensions in the medial-lateral direction provide greater resistance to anterior avulsion.

[0073] The illustrated component is configured for cementless fixing. That is, the component preferably includes a cementless fixing surface on the opposing surface and the outside of the wall 20. Such a coating may be provided on one or more of the elongated pegs. Such surfaces may be porous or microporous coatings having or not having an active surface such as hydroxyapatite.

[0074] The components shown in Figures 1-4 are merely examples, and other designs are possible. Several exemplary alternative designs are shown in Figures 5a-5e. The same reference numbers are used for the same feature parts. The feature parts described above for the components shown in Figures 1-4 may also be present in the components in Figures 5a-5e, although they are not described below.

[0075] Figure 5a shows a tibial component 40 including a plate 12 similar to the plate described above. This component includes only a single fixation peg 14 positioned on the anterior portion 29 of the plate. There are no pegs or other fixation devices on the opposing surface of the plate posterior to the elongated fixation peg 14. In the illustrated example, this single fixation peg is positioned at approximately one-fifth of the longitudinal axis length of the component. It should be understood that the single fixation peg may be positioned at other locations, for example, one-quarter or one-third of the longitudinal axis length of the component.

[0076] Figure 5b shows a tibial component 44, which includes two elongated oblique pegs 14 and 16, similar to the components shown in Figures 1 to 4. The pegs 14 and 16 of component 44 are covered with a cementless fixation coating 46 (e.g., a porous or microporous coating) which may or may not have an active surface such as hydroxyapatite. The coating is not provided (i.e., is absent) in a region 48 of each peg. In this example, the region 48 is the base region adjacent to the opposing surface 22.

[0077] In the illustrated example, the fixing coating is applied to most of the surface of the peg, but not to the base region that extends 1-2 mm below the opposing surface 22 of the tibial component.

[0078] The coating can be omitted, for example, by shielding a portion of the peg (e.g., the base 48) when applying a porous coating. This has the effect of making the diameter of the shielded area of ​​the peg smaller than the maximum diameter of the coated portion of the peg. The porous coating (with or without hydroxyapatite) may be about 0.35 to 0.4 mm thick. By omitting such a coating in one area of ​​the peg, the diameter of that area becomes about 0.7 to 0.8 mm smaller than the diameter of the rest of the peg. This narrowed area may still be coated with hydroxyapatite.

[0079] By providing a narrower area in each fixing peg, the peg becomes less likely to come loose once it is in place. Providing a narrower area at the base of each peg can also reduce the likelihood of bone fracture. Figure 5c shows an alternative example of a tibial component 50 having a pair of elongated pegs 14, 16, where each peg has a base area 48 adjacent to the opposing surface and smaller than the maximum diameter of the peg. Such narrow areas can be formed as described above (by omitting the coating in this area) or by other methods such as applying the coating and then crimping or compressing the peg.

[0080] Figure 5d shows a further alternative example of the tibial component 52 having a pair of elongated pegs 54, 56, each peg being tapered. As shown with respect to the components in Figures 1 to 5c, the pegs may have parallel planes, but as shown in Figure 5d, they may have a slight taper (e.g., a taper with a slight angle). Such a taper may make peg insertion easier and / or make peg fixation stronger. The entire peg does not need to be tapered. Alternatively, only the tip of the peg may be tapered. This, too, is helpful for insertion.

[0081] All components shown in Figures 1 to 5c have pegs (including multiple pegs) with circular tips 58, particularly flat ends with circular edges, which can maximize the fixing area. Component 60 shown in Figure 5e differs in that each peg has a spherical end 62. This also helps in insertion.

[0082] The component shown in Figure 5e further includes one or more barbs 64 configured to resist the component coming off after installation. Alternatively, circumferential barbs can be formed by omitting, crimping, or machining areas of the porous coating on the peg.

[0083] The components described herein can be fabricated from any suitable strength and bioinert material, such as cobalt-chromium or titanium alloys. Any porous coating capable of allowing or promoting bone endografting, such as plasma-sprayed titanium or tantalum, can be applied to the bone-contact surfaces of the components.

[0084] Figures 6 and 7 show anterior and lateral views, respectively, of the tibial component 10 fitted to the patient's tibia 66. As described above, oblique pegs positioned anterior to the tibia, in this case two oblique pegs 14 and 16, are used to fix the tibial component. The pegs are oblique and are located primarily in the anterior-posterior plane of the component, inclined distally and posteriorly (inferiorly and posteriorly). Positioning the pegs anterior to the tibia and inclining them relative to the vertical leaves sufficient space to drive the pegs into the tibia, even in the presence of the femur 104, and all ligaments resist joint extension.

[0085] Such components can be attached using cement, but are ideal for cementless attachment. Cementless components (i.e., components with cementless fixation surfaces) require drilling one or more holes slightly narrower than the peg(s) in the appropriate location on the resected tibia, and then pressing the peg(s) into the holes to form a crimp. Cemented components can be inserted into holes with less stringent tolerances, allowing space for a cement mantle between the peg and the bone.

[0086] However, drilling oblique parallel holes in surgical procedures is not easy, and to assist in the insertion process, surgeons may use a guide device of the type shown in Figure 8, 70.

[0087] The guide device 70 includes a guide plate 72 and at least one drill guide (in this case, a first drill guide 74 and a second drill guide 76).

[0088] The guide plate 72 is shaped to mimic the plate of the tibial component to be fitted, such as the plate 12 of the tibial component 10 described above. Therefore, in the illustrated example, the guide plate 72 is substantially flat and has a contour shaped to mimic the natural shape of the patient's tibia. Since the illustrated example is a guide plate for a medial tibial component, this plate is formed in a roughly C-shape on the medial side and includes an upright lip on the opposing lateral side.

[0089] The guide plate 72 has a front end 84, a rear end 86, an inner portion, and an outer portion. The width of the plate in the inward and outward directions is defined between the inner portion and the outer portion, and the longitudinal front-to-rear axis 88 extends from the outer portion between the front end and the rear end by approximately one-third (i.e., 1 / 3W) of the width of the guide plate, defining the longitudinal axis length of the guide plate.

[0090] A virtual line 90 extending inward and outward across the guide plate divides the guide plate into a front portion 89 and a rear portion 91 along the inward and outward directions. In the illustrated example, the front portion includes the portion defined by the front 50% of the longitudinal axis length L of the guide plate (also referred herein as the front 50% of the guide plate), while the rear portion includes the portion defined by the rear 50% of the longitudinal axis length L of the guide plate (i.e., the remainder of the guide plate, also referred herein as the rear 50% of the guide plate).

[0091] The first drill guide 74 is configured to guide the drill along the first drill shaft 92 through the guide plate 72. The second drill guide 76 is configured to guide the drill along the second drill shaft 94 through the guide plate 72. The first drill shaft 92 and the second drill shaft 94 are substantially parallel to each other and positioned at an angle of 96° with respect to the longitudinal front-to-back axis. This angle may be in the range of 45 to 70°, for example, in the range of 55 to 65°, and in the illustrated example, it is approximately 60°.

[0092] The drill guides 74 and 76 may be provided as hollow tubes, such as cylindrical bodies, through which a surgical drill bit can pass. The hollow diameter of each cylinder may be less than or equal to the diameter of the peg of the component to be mounted (for example, 0.5 mm or 1 mm narrower).

[0093] In the illustrated example, the guide plate includes a length in the front-to-back direction defined as described above with respect to the longitudinal axis 88, the first drill guide 74 is positioned at one-fifth of the length of the guide plate 72, and the second drill guide 76 is positioned at half the length of the guide plate.

[0094] Such a guide device 70 can be used to drill a pair of parallel oblique holes into which the elongated pegs 14, 16 of the tibial component of the type described herein can be fitted. The drill guide can be spaced differently or angled differently as needed. The spacing and angle of the drill guide must match the spacing and angle of the pegs of the component to be fitted.

[0095] The guide may include a hole 98 that penetrates the guide plate. In the illustrated example, the hole 98 is located between the first drill guide and the second drill guide, and is located inside them.

[0096] The following describes an exemplary implantation method with reference to Figures 9, 10, and 11. The first step is to excise the surface of the patient's tibia to be replaced and prepare it for receiving the implant (or trial implant). Next, the guide device 70 is placed on the excised surface and fixed in place.

[0097] The guide device can be secured by a pin 100 or other suitable temporary fixation member that passes through the hole 98. A clamp ( schematically illustrated in 102) may be provided to engage between the patient's femur 104 and the posterior aspect of the guide plate 72. Such a clamp may be attached to the upper surface of the back of the guide plate. This clamp is adjusted to firmly press the guide device 70 against the tibia by pushing it upward onto the surface of the superior femoral condyle.

[0098] As shown in Figure 10, once the guide is fixed to the surface of the resected tibia, an anterior implant hole 105 is drilled in the resected tibia at an angle to the surface of the resected tibia, as schematically indicated by arrow 106.

[0099] As shown in Figure 11, the stabilizing rod 108 is then inserted into the drilled anterior hole to stabilize the guide. Subsequently, the second hole 107 is drilled into the resected tibia at an angle to the resected tibia surface, as schematically indicated by the arrow 110.

[0100] The two drill holes mentioned above are parallel to each other and both have the same angle of inclination with respect to the resected tibia surface.

[0101] The surgeon can drill the first and second holes using a drill schematically indicated by arrows 106 and 110. Such a drill may include a drill stop. The drill stop is operable to strike a corresponding drill stop on the surface of the guide instrument (e.g., on the guide plate and / or drill guide) when the hole has been drilled to a predetermined depth (e.g., 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, or 12 mm) to prevent the surgeon from drilling the hole too deep unintentionally. If a tapered hole needs to be drilled, such a drill may have a tapered drill bit.

[0102] Subsequently, the tibial component of the type described above (i.e., a tibial component with a pair of parallel, angled, elongated fixing pegs) can be fitted into the drilled holes. These holes can be drilled to be slightly narrower than the pegs of the implant component to facilitate tightening.

[0103] The type of tibial component described herein can reduce the likelihood of posterior tibial depression and / or fracture occurring after tibial surface replacement surgery. The oblique nature of the pegs resists the component from floating forward after implantation. It should be understood that any number of pegs may be provided, e.g., one, two, three, four, or five pegs. If two or more pegs are provided, all pegs must be parallel to each other in order to perform cementless implantation. The pegs can be positioned at any location within the anterior portion of the component, but it is preferable that they not be too close to the outer edge of the plate (the medial edge in the illustrated example). For example, the pegs can be positioned at any location beyond one-third of the plate's width from the outer edge, e.g., more than half the plate's width from the outer edge (e.g., 1 / 2 to 4 / 5 of the plate's width from the outer edge).

[0104] The absence of fixation pegs on the posterior portion of the component means that the component can be fitted in a way that reduces damage to the posterior portion of the patient's tibia. By not including a keel or large-diameter pegs, the risk of fracture is further reduced, as is the risk of surgical errors such as cutting the keel groove too deeply or damaging the posterior cortex.

[0105] Conventional components, through keel or large-diameter peg compression, can generate tension on the upper part of the surface-reconstructed condyle, increasing the risk of fracture. In contrast, using relatively thin, oblique pegs as described herein allows for fixation with minimal risk of fracture. The use of thin (high aspect ratio / elliptical) pegs requires minimal bone removal in the upper part of the tibia, leaving a significant amount of bone intact to transmit tension and prevent fracture. Furthermore, the pegs are positioned far from the cortex.

[0106] The advantages of positioning the elongated fixation pegs on the anterior portion of the tibial component have been described above. The inventors have also found that tibial components with a keel can benefit from positioning the keel further forward. By positioning the keel further forward compared to the current keel, damage to the posterior portion of the tibia can be reduced (as described above). Furthermore, by positioning the keel further forward, the need to work closer to the posterior portion of the tibial platform is reduced. This can be difficult for surgeons because it involves the use of novel, minimally invasive techniques that restrict access to the posterior portion of the joint.

[0107] For reference and comparison, Figure 12 shows a lateral view and a front view (with a support surface at the top) and a top view (with an opposing surface at the top) of a prior art tibial component 100. This component is a medial component of size A.

[0108] Similar to the components described above, the tibial component 100 includes a plate 112 configured to replace the articular surface of the patient's tibia, in this case the medial tibial support surface. This plate includes a support surface 118 that replaces the patient's tibial support surface when fitted. Thus, the support surface 118 is shaped to either work directly with the patient's femur (or femoral replacement component) or with a support component positioned between the tibial component and the femur / femoral replacement component.

[0109] In the illustrated example, plate 112 is substantially flat and has a contour shaped to mimic the natural shape of the patient's tibia. Since the illustrated example is a medial tibial component, this plate is formed in a roughly C-shape on the medial side and includes an upright wall or lip 120 on the opposing lateral side, the upright wall or lip 120 intended to abut against the central tibial tuberosity of the patient's tibia when the component is fitted. The lateral tibial component is a mirror image of the illustrated component. It should be understood that this plate may have a different shape, for example, it may be roughly circular or elliptical.

[0110] The opposing surface 122 of the plate is configured to be fixed to the proximal end of the patient's tibia, as detailed below.

[0111] The plate 112 has a front end 124, an inner part 125, a rear end 126, and an outer part 127. The width W of the plate in the inward-outward direction is defined between the inner part and the outer part, and the longitudinal front-to-rear axis 128 extends from the outer part between the front end and the rear end by about one-third of the width of the plate (i.e., 1 / 3W), defining the longitudinal axis length L of the plate.

[0112] Primary fixation is essential for maintaining the component in a quiescent state after transplantation, allowing bone to grow within the implant and anchor to it, thereby achieving secondary fixation. For this reason, the illustrated prior art tibial component includes a keel 175 projecting from the opposing surface. The keel 175 is an elongated projection whose length in the anterior-posterior direction is greater than its width in the medial-lateral direction. The keel projects distally from the opposing surface and, in this example, is substantially perpendicular to the opposing surface (although this is not essential). The keel includes a base 177 adjacent to the opposing surface and an apic 179 distal to the base. The keel also includes a medial wall 181 and a lateral wall 183.

[0113] The keel 175 of the conventional component shown in Figure 12 is positioned in the center of the opposing surfaces. In this example, "center" means being positioned in the center with respect to the front-to-rear axis 128. In particular, the keel is positioned such that the distance d1 between the leading edge 185 of the keel and the front end 124 of the plate is approximately the same as the distance d2 between the trailing edge 187 of the keel and the rear end 126 of the plate. The keel is not positioned in the center with respect to the width W of the plate, but rather, similar to the peg described above, it is positioned about 1 / 3 W from the outer edge.

[0114] Typical dimensions of a plate with a central keel of the type shown in Figure 12 are as follows: AP shaft length L = 44.92 mm Keel length = 25.92 mm d1=d2=9.50mm Distance between the keel and the outer part = 1 / 3W = 7.98 mm

[0115] In contrast, Figure 13 shows an alternative unicondylar tibial component 200. The same reference numbers are used for the same components, and for brevity, the descriptions of these components are not repeated.

[0116] Unlike the components shown in Figure 12, component 200 includes a keel 275 that is not centrally located. Specifically, the distance d3 between the front edge 285 of the keel and the front end 124 of the plate is smaller than, and even smaller than, the distance d4 between the rear edge 287 of the keel and the rear end 126 of the plate. In this example, the keel 275 is the same length as the keel 175 of the prior art, but is positioned closer to the front rim of the plate than to the rear rim. As mentioned above, the keel is not centrally located with respect to the width W of the plate, but rather, like the pegs described above, is positioned about 1 / 3 W from the outside.

[0117] The exemplary dimensions of a plate with the type of front keel shown in Figure 13 are as follows: AP shaft length L = 44.92 mm Keel length = 25.92 mm d3 = 7.94 mm d4 = 11.08 mm Distance between the keel and the outer part = 1 / 3W = 7.98 mm

[0118] Therefore, it was found that the keel of component 200 is positioned approximately 1.5 mm further forward than in the case of a conventional keel. However, the keel may be positioned even further forward if necessary.

[0119] Distance d3 may be 50-85% of distance d4, for example, 60%, 65%, 70%, 75%, or 80%.

[0120] Therefore, it is useful to include a virtual line 130 that divides the plate 112 into a front portion 129 and a rear portion 131 along the inward-outward direction. In the illustrated example, the front portion includes the portion defined by the front 76% of the longitudinal axis length L of the plate (also referred to herein as the front 76% of the plate), while the rear portion includes the portion defined by the rear 24% of the longitudinal axis length L of the plate (i.e., the remainder of the plate, also referred to herein as the rear 24% of the plate).

[0121] It should be understood that the dividing line 130 may divide the longitudinal axis in a different way, for example, the front portion may be 70% of the front of the plate and the rear portion may be 30% of the remaining (rear) portion of the plate. The front:rear ratio of the front portion to the rear portion of the plate may be 77:23 or less, for example, 70:30, 65:35, 60:40, 55:45 or 50:50. Thus, as described above, the rear portion includes at least 23% of the plate, preferably 24%, 25%, 26%, 27%, 28%, 29% or more, as defined according to the longitudinal axis length.

[0122] Figures 14 and 15 show tibial components 300 and 400 similar to the tibial components in Figures 12 and 13, except that the keels 375 and 475 of the components are tapered. As used herein, “tapered” means that the medial wall 381 and lateral wall 383 taper inward from the base 377 to the tip 379. That is, the keel is narrower (i.e., thinner) towards the tip than at the base adjacent to the opposing surface. Such a tapered keel can make the interlocking with the tibia more secure and reduce the possibility of loosening over time.

[0123] The taper angle may be 0.5 to 4°, for example, 1°, 2°, or 3°. In cases where the keel protrudes from the plate in a direction perpendicular to the opposing surface, the taper angle may be measured relative to a plane perpendicular to the opposing surface.

[0124] Figure 16 shows a prior art tibial component 100a, similar to the component in Figure 12, except that the component in Figure 16 is of size G. Similarly, Figures 17–19 show component 200a, 300a, and 400a of size G, similar to the component of size A shown in Figures 13–15. For brevity, the same reference numerals are used, and it should be understood that the above descriptions for Figures 12–15 also apply to Figures 16–19.

[0125] The sides of the keel shown in any of Figures 12 to 19 may include a surface that promotes bone endografting, such as a porous or microporous coating of the type described above.

[0126] However, the inventors have recognized that it is preferable to keep part or all of the keel surface smooth, even in cementless components.

[0127] When implanting a keel into a patient's tibia, a keel groove is typically cut into the prepared tibia surface. The keel of the tibial component is then inserted obliquely into the groove from the posterior inferior direction, and when the keel reaches the posterior end of the groove, the tibial component is rotated to a horizontal position and pushed downward into the groove. The inventors have noticed that keels with a rough surface designed for bone endografting can become lodged in the prepared keel groove, acting as a file and widening the groove, which can result in poor fit and loosening over time.

[0128] Therefore, the sides of the keel shown in any of Figures 12 to 19 may be smooth. That is, the outer surface of the keel does not need to have a rough surface, such as a porous or microporous coating, designed to promote bone endografting. Since sufficient bone endografting can occur on the underside of the tibial platform, the need to grow bone on the sides of the keel is limited. Smoothing the sides of the keel can avoid the aforementioned grating effect and improve the interlocking of the components.

[0129] Figures 20 and 21 show alternative exemplary keels 575 and 675 having a smooth insertion surface. In this specification, “insertion surface” refers to the surface of the fixation mechanism that is operable to be initially inserted into the bone cavity in order to guide the rest of the fixation mechanism. If such an insertion surface is rough, its abrasive effect is significantly greater than any abrasive effect from the rest of the fixation mechanism. Therefore, by providing a smooth insertion surface, the abrasive effect can be significantly reduced. The rest of the fixation mechanism may be provided with (uncovered) surface structures or treatments that promote bone endografting and still maintain a large covering surface area for bone endografting.

[0130] In particular, the keel shown in Figures 20 and 21 includes smooth outer rims 590 and 690. The smooth outer rim includes at least a portion of the posterior (rear) edge 587 and at least a portion of the distal edge 579 of the keel. In the specific examples shown in Figures 20 and 21, the outer rim substantially includes the entire posterior edge 587 and the distal edge 579, and part or all of the anterior (front) edge 585.

[0131] The remaining surfaces of the keel (i.e., surfaces other than the smooth insertion surface) may be coated with a cementless coating to improve secondary fixation. For example, in the illustrated example, a pocket 692 is defined by the outer rim. This pocket has a depth equal to or greater than the thickness of the porous or microporous coating 594, so that such a coating can be contained within the pocket and be substantially coplanar with or below the smooth outer surface of the outer rim. The depth may be, for example, 0.35 to 0.4 mm or more.

[0132] A properly positioned and tightly fitted keel contributes to cementless fixation by holding the implant in place until bone endografting progresses. An extension of keels with smooth or partially smooth surfaces is a keel with a rough or partially rough surface designed for bone endografting, but covered with a bioabsorbable material such as calcium paste. The bioabsorbable material provides a smooth insertion surface that is absorbed over time, and allows for growth into the rough cementless fixation surface if a larger bone attachment surface is required.

[0133] It should be understood that the types of pegs described above, as well as other fastening mechanisms such as the more common non-angled or non-forward pegs, can also benefit from smooth sides and / or smooth insertion surfaces. Figure 21 shows a peg 614 with a smooth insertion area and pocket. The insertion area is the tip of the peg in the illustrated example. This tip is round, and in particular partially spherical, to further assist in insertion.

[0134] In any of the exemplary embodiments described above, the thickness of the plate of a smaller implant may be less than that of a larger implant in order to minimize bone removal, as described in the prior patent publication US2013 / 0166073, and / or the depth of the keel (or peg) of a smaller implant may be less than that of a larger implant in order to minimize tibial fracture. The contents of US2013 / 0166073 are incorporated herein by reference.

[0135] Those skilled in the art will understand that modifications may be made to the embodiments described above without departing from the claims set forth below. Features from different examples can be combined with each other. Therefore, it should be understood that the present invention is not limited to the above examples, but is defined by the claims. [Explanation of symbols]

[0136] 10 Tibial components 12 plates 14 (First) Peg 16 (2nd) peg 18 Support surface 20 Wall / Lip 22 Opposing surfaces (of the plate) 24 (Front end of the plate) 25 (Inner part of the plate) 26 (Rear end of the plate) 27 (The outer part of the plate) 28 Front-rear axis (longitudinal axis) 29 (Front part of the plate) 30 division lines / imaginary lines 31 Rear part (of the plate) 32 (First) peg shafts 34 (Second) peg shaft 36 angles 40 Tibial component 44 Tibial component 46. ​​Cementless fixing coating Area of ​​48 pegs 50 Tibial component 52 Tibial component 54 pairs of pegs 56 pairs of pegs 58 Circular tip 60 Tibial component 62 Spherical ends 64 barbs 66 Tibia 70 Guide Tools 72 Guide Plate 74 (First) Drill Guide 76 (Second) Drill Guide 84 Front end (of the guide plate) 86 (Rear end of guide plate) 88 Front-rear axis (longitudinal axis) 89 Front part (of the guide plate) 90 virtual lines 91 Rear part (of the guide plate) 92 (First) Drill Shank 94 (Second) Drill Shank 96 angle 98 holes 100 Tibial Component (Size A) / Pin 100a Tibial component (size G) 102 Clamp 104 Femur 105 Anterior implant hole 106 Arrow 107 The second hole 108 Stabilizing Rod 110 Arrow 112 Plates 118 Support surface 120 Wall / Lip 122 Opposing surface (of the plate) 124 (Front end of the plate) 125 (Inside of the plate) 126 (Rear end of the plate) 127 Outer part (of the plate) 128 Front-rear axis (longitudinal axis) 129 (Front part of the plate) 130 dividing lines 131 Rear part (of the plate) 175 keels 177 Base (of the keel) 179 (Keel) tip 181 (Inner wall of the keel) 183 (Keel's) outer wall 185 (Keel's) leading edge 187 (Keel's) trailing edge 200 Tibial Component (Size A) 200a Tibial component (size G) 275 keels 285 (Keel's) anterior edge 287 (Keel's) rear edge 300 Tibial Component (Size A) 300a Tibial component (size G) 375 keels 377 Base (of the keel) 379 (Keel) tip 381 (Inner wall of the keel) 383 (Keel's) outer wall 400 Tibial Component (Size A) 400a Tibial component (size G) 475 keel 575 Kiel 579 (Keel's) distal edge 585 (Keel's) anterior edge 587 (Rear edge of the keel) 590 Outer rim 594 Porous coating 614 pegs 675 Kiel 690 Outer rim 692 pockets d1 distance d2 distance d3 distance d4 distance A size G size L Length W width

Claims

1. It is a unicondylar tibial component, A plate having a support surface and an opposing surface configured to be fixed to the proximal end of the patient's tibia, wherein the plate further comprises an anterior end, an lateral end, a posterior end, and an lateral end, the width W of the plate in the inward-outward direction defined between the lateral end and the lateral end, and the longitudinal anterior-posterior axis extending from the lateral end between the anterior end and the posterior end by approximately one-third (i.e., 1 / 3W) of the width of the plate, defining the longitudinal axis length L of the plate, A first elongated peg protrudes from the opposing surface in the front portion and defines the first peg shaft, A second elongated peg protrudes from the opposing surface in the front portion and defines the second peg shaft. The first and second peg shafts are positioned at an angle of 45° to 70° with respect to the longitudinal front-to-back axis, and are substantially parallel to each other such that the first and second pegs protrude rearward and distally from the plate. The front portion of the plate includes a portion defined by 60% or less of the front of the longitudinal axis length L of the plate, while the rear portion of the plate includes a portion defined by 40% or more of the remaining rear of the longitudinal axis length L of the plate, and no pegs or other fastening devices are placed on the rear portion of the opposing surface. The first and second elongated pegs are positioned at a location that is more than half the width W of the plate in the inward-outward direction from the outer edge of the plate. The aforementioned component is a unicondylar tibial component configured for cementless fixation using a compression fit.

2. The unicondylar tibial component according to claim 1, wherein the first and second peg axes are arranged at an angle of approximately 60° with respect to the longitudinal anterior-posterior axis.

3. The unicondylar tibial component according to claim 1 or 2, wherein one or more of the elongated pegs preferably have a high aspect ratio, and each peg preferably has a length of 6 to 12 mm and a maximum diameter of 4 to 8 mm.

4. (i) One or more of the elongated pegs have an elliptical cross-section, or (ii) The unicondylar tibial component according to any one of claims 1 to 3, wherein one or more of the elongated pegs are tapered.

5. The unicondylar tibial component according to any one of claims 1 to 4, wherein one or more of the elongated pegs have a round or tapered tip.

6. The unicondylar tibial component according to any one of claims 1 to 5, wherein the first elongated peg is positioned at one-fifth of the anterior-posterior axis length, and the second elongated peg is positioned at half the anterior-posterior axis length.

7. The unicondylar tibial component according to any one of claims 1 to 6, wherein one or more of the elongated pegs include one or more barbs.

8. The unicondylar tibial component according to any one of claims 1 to 7, wherein each of the elongated pegs is provided with a cementless fixing coating, the coating is not present in any region of each peg, and the diameter of each region is narrower than the maximum diameter of the covered peg.

9. The unicondylar tibial component according to claim 8, wherein the coating is not present in the base region of each peg adjacent to the opposing surface, so that the diameter of each base region is narrower than the maximum diameter of the coated peg.

10. The unicondylar tibial component according to any one of claims 1 to 9, wherein one or more of the elongated pegs include a region narrower than the maximum diameter of the peg.

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