Constrained prosthetic knee

Abstract

To provide a constrained prosthetic knee.SOLUTION: A system includes a prosthesis assembly for a constrained knee including a tibial baseplate, a mobile bearing, and a fixed bearing. The tibial baseplate can include a distal surface and a proximal surface that can be configured to receive a hinge post. The mobile bearing can be configured to couple with the tibial baseplate and to rotate about at least a first axis approximated by a centerline of the hinge post. The rotation about at least the first axis can be limited by at least the first engagement feature. The fixed bearing can be configured to be coupled to the tibial baseplate. The fixed bearing can be restrained from rotating about the first axis by at least the first engagement feature of the tibial baseplate. The tibial baseplate can be configured to be assembled with either the mobile bearing or the fixed bearing.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] Claim of Priority This application claims the benefit of U.S. Provisional Patent Application No. 63 / 434,590, filed Dec. 22, 2022, and U.S. Patent Application No. 18 / 526,737, filed Dec. 1, 2023, the entire disclosures of which are hereby incorporated by reference herein in their entireties and for which priority is claimed herein.

[0002] The present subject matter generally relates to orthopedic prostheses. More specifically, the present disclosure relates to orthopedic prostheses used in constrained knee arthroplasty.

Background Art

[0003] Orthopedic surgeries and prostheses are commonly utilized to repair or replace damaged bones and tissues within the human body. Generally, the knee is formed by a condyle at the distal portion of the femur, the lower surface of which is supported by a corresponding shaped proximal surface plateau of the tibia. The femur and tibia are connected by ligaments such as the posterior cruciate ligament, the lateral collateral ligament, the medial collateral ligament, and the anterior cruciate ligament. These ligaments provide stability to the knee joint.

[0004] Artificial knee joints can be considered either constrained or unconstrained. A constrained artificial knee system can include a femur and tibia prosthesis, which are mechanically linked or constrained relative to each other to limit relative movement between the femur and tibia prostheses. Common mechanisms for such mechanical linkage can include hinges, bands, or other linkage structures. An unconstrained artificial knee system includes femur and tibia prostheses that are not mechanically linked. Unconstrained knees utilize the patient's remaining ligaments and other soft tissues to provide joint stability. Constrained artificial knees are particularly useful in cases where the patient has experienced ligament loss or the remaining ligaments do not provide adequate support and stability to the knee.

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present disclosure generally relates to improved constrained knee prostheses, particularly those utilizing a hinge post. Some constrained knee prostheses having a hinge post utilize a design in which the femoral component (and hinge post) can move freely proximally / distally relative to the tibial baseplate and tibial bearing component. The inventors of the present disclosure recognized a need for a system that provides a prosthesis that is reconfigurable for either a mobile bearing system or a fixed bearing system. This system can include components that can be assembled to form a mobile bearing constrained knee prosthesis and a fixed constrained knee prosthesis.

[0006] In the figures of the accompanying drawings, various embodiments are shown by way of example. Such embodiments are illustrative and are not intended to be an exhaustive or exclusive embodiment of the subject matter.

Brief Description of the Drawings

[0007]

Figure 1

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[0008] The present application relates to a system including a constrained knee prosthesis. The system can include, for example, a set of components such as a tibial tray or baseplate, a shackle, a femoral component, a hinge post, a polybox, an axle bushing, etc. The set of components can be configured to be compatible with a tibial bearing component. In an embodiment, the system can include a movable tibial bearing component or a fixed tibial bearing component, which can be replaceable at the discretion of the surgeon. The movable tibial bearing component can be configured to limit rotation (or movement) about at least one axis when engaged with one or more engagement mechanisms of the tibial tray, compared to the movable tibial bearing component. The fixed bearing component can prevent or significantly limit rotation (or movement) about at least one axis by contacting one or more engagement mechanisms of the tibial tray.

[0009] In another embodiment, the system can include a component set, a movable tibial bearing component, and a press-fit insert. In such an embodiment, the press-fit insert can be configured to fill the space between the movable tibial bearing component and one or more engagement mechanisms of the tibial tray to further limit or prevent rotation or movement of the tibial bearing component about one or more axes relative to the tibial bearing tray.

[0010] To better understand knee arthroplasty, it may be useful to understand the relationship between the bone cuts and the bone that can be formed to orient various provisional and permanent prosthetic components within the knee joint. FIGS. 1 and 2 illustrate some features and orientations of the knee joint structure. In FIG. 1, a front view of the lower limb 102 including the femur 104 and the tibia 106 illustrates various lower limb axes. The femur 104 generally has an anatomical axis 108 that coincides with its intramedullary canal. The femur 104 also has a mechanical axis 110 or load axis that runs from the center of the femoral head 112 to the center of the knee joint 114. The angle 116 extending between these two axes varies among patient populations but is generally between 5 and 7 degrees. Similar to the femur 104, the tibia 106 generally has an anatomical axis that coincides with its intramedullary canal. The mechanical axis 118 of the tibia 106 runs from the center of the knee joint 114 to the center of the leg portion 120 and is generally collinear with its anatomical axis.

[0011] The joint line 122, which is the center about which the knee joint 114 flexes, is approximately parallel to the line passing through the medial and lateral femoral condyles 124 and the tibial plateau 126. Although illustrated as intersecting at right angles in FIG. 1, the joint line 122 can extend at an varus or valgus angle with respect to the mechanical axes 110 and 118 of the femur 104 and the tibia 106, respectively. Typically, during a partial or total replacement, a plurality of portions of the distal end of the femur 104 or the proximal end of the tibia 106 are resected parallel or approximately parallel to the joint line 122 and thus orthogonal to the mechanical axes 110 and 118 as indicated at 128 and 130, respectively.

[0012] A typical knee can move between an extended state where the longitudinal axes of the femur 104 and the tibia 106 are essentially parallel, and a flexed state where the longitudinal axes of the femur 104 and the tibia 106 form an angle of approximately 140 degrees with respect to each other. In an embodiment, the extended state can be limited to + / - 10 degrees, and the flexed state can be much less than 140 degrees. For example, the flexed state can include a limit where the longitudinal axes of the femur 104 and the tibia 106 form an angle of approximately 90 to 140 degrees with respect to each other.

[0013] Figure 2 illustrates a closer view of the knee joint 114 and its coordinate system, where the medial / lateral axis 202 approximately corresponds to the joint line 122 (see Figure 1), the proximal / distal axis 204 approximately corresponds to the mechanical axes 110 and 118 (see Figure 1), and the anterior / posterior axis 206 is approximately perpendicular to the other two axes. The arrows can represent positions along each of these axes, representing the medial / lateral 208, anterior / posterior 210, and proximal / distal 212 positioning of the inserted prosthesis components. Rotations about each of these axes can likewise be represented by arrows. Rotation about the proximal / distal axis 204 can correspond anatomically to external rotation of the femoral component, while rotations about the anterior / posterior axis 206 and the medial / lateral axis 202 can correspond, respectively, to the component's extension plane gradient and varus / valgus angle. Depending on the position of the formed proximal tibial cut 130 (see Figure 1), the varus / valgus angle 214, extension plane angle 216, external rotation 218, or joint extension gap can be affected. Similarly, the position of the distal femoral cut 128 (see Figure 1) can affect the location of the joint line 122, the extension gap, the varus / valgus angle 214, or the extension plane angle 216.

[0014] As used herein, the terms "proximal" and "distal" should be given their generally understood anatomical interpretations. The term "proximal" generally means in the direction toward the patient's torso, and the term "distal" means in the direction opposite proximal, i.e., away from the patient's torso. It should be understood that the terms "proximal" and "distal" should be interpreted as if the patient were standing with the knee joint extended. The intent is to distinguish the terms "proximal" and "distal" from the terms "front" and "back". As used herein, the terms "front" and "back" should be given their generally understood anatomical interpretations. Thus, "back" means the posterior part of the patient, e.g., the back of the knee. Similarly, "front" means the anterior part of the patient, e.g., the front of the knee. Thus, "back" means the direction opposite "front". Similarly, the term "medial" means the direction opposite "lateral". The terms "medial / lateral" mean from medial to lateral or from lateral to medial. The terms "proximal / distal" mean from proximal to distal or from distal to proximal. The terms "front / back" mean from front to back or from back to front.

[0015] As used herein, the "periphery" of the tibial baseplate means any periphery as seen in a top view, e.g., generally in a transverse anatomical plane. Alternatively, the periphery of the tibial baseplate may be any periphery as seen in a bottom view, e.g., generally in a cross-section, of the distal surface adapted to contact the resected proximal surface of the tibia.

[0016] The term "micromotion" means the small movement that may exist between prosthesis components, e.g., between the tibial baseplate and the capture element, when a force is applied. Such small movement may result from material deformation in one or both of the interacting components, or may be the result of a small space or clearance between them. Micromotion is distinguished from larger movement of components such as proximal / distal movement of the femoral component relative to the tibial baseplate and tibial bearing components.

[0017] Figure 3 shows a constrained knee prosthesis assembly 300. The prosthesis assembly 300 can include a tibial baseplate 302, a tibial bearing component 304 (which may also be referred to as a meniscus component, a polymer, an articular component, or a bearing), a femoral component 306, and a hinge post 308.

[0018] The tibial bearing component 304 can be coupled to and positioned on the proximal surface 310 of the tibial baseplate 302. The tibial bearing component 304 can be formed of a polymeric material such as ultra-high molecular weight polyethylene (“UHMWPE”). The tibial bearing component 304 can be configured to articulate with the femoral component 306 through flexion and extension of the knee joint, as is known in the art. The prosthesis assembly 300 has a femoral component 306 and a tibial baseplate 302 that are mechanically coupled to each other. This is accomplished by the hinge post 308 and other components that are further illustrated and discussed in Figure 4. The hinge post 308 is coupled to the femoral component 306 and is received within the recess 309 of the tibial bearing component 304 and the recess 322 (see Figure 4) of the tibial baseplate 302.

[0019] Figure 4 shows an exploded view of the prosthesis assembly 300, the tibial baseplate 302, the tibial bearing component 304, the femoral component 306, the hinge post 308, and further illustrates a hinge axis 312, a poly box 314, a shaft bushing 316, a shackle 318, and a bushing.

[0020] The hinge post 308 is connected to the femoral component 306 via a shackle 318, a shaft bushing 316, and a hinge shaft 312. The distal portion of the shackle 318 is received within a recess 309 in the tibial bearing component 304, and the distal portion is threaded or otherwise connected to the hinge post 308. The hinge post 308 extends distally through the recess 309 of the tibial bearing component 304 and is received within a recess 322 of the tibial base plate 302. The recess 322 of the tibial base plate 302 that receives the hinge post 308 can be formed at least in part by a keel 324 of the tibial base plate 302. The hinge post 308 is movable relative to the tibial bearing component 304 or the tibial base plate 302, e.g., rotatable or extendable. The hinge post 308 can be rotatably connected to the femoral component 306 via the hinge shaft 312. Thus, the longitudinal axis LA defining the centerline of the hinge post 308 can define the rotational / articulation axis ARA for the knee joint when the femoral component 306 and the tibial base plate 302 are mechanically connected.

[0021] When assembled, the shackle 318 can be installed between opposing walls of the polybox 314. When assembled on the hinge shaft 312, the shaft bushing 316 is further positioned inside an opening on the proximal portion of the shackle 318. The shackle 318 and the hinge post 308 can be formed of a suitable material such as a titanium alloy, a cobalt-chromium alloy, etc., while the shaft bushing 316 and the polybox 314 can be formed of a different material such as a plastic like UHMWPE. The shaft bushing 316 can function as a bearing between the shackle 318 and the hinge shaft 312. The polybox 314 can function as a bearing between the femoral component 306 and the shackle 318.

[0022] The prosthesis assembly 300 of FIG. 4 shows a system 326 of components where knee extension is not restricted by the capture elements or other features of the prosthesis assembly 300. Thus, system 326 provides components that are configured to fully extend when assembled. Thus, as previously discussed, reliance is placed on the knee soft tissue to limit extension between the femoral component 306 and the tibial baseplate 302 and tibial bearing component 304. The bushing 320 can be configured to insert at least within the recess 322 of the tibial baseplate 302. The bushing 320 can also be inserted within or through the recess 309 (see FIG. 3) of the tibial bearing component 304 in some embodiments. The bushing 320 can be configured to receive at least a portion of the hinge post 308. The bushing 320 can function as a bearing between the hinge post 308 and the tibial baseplate 302. The hinge post 308 can be generally movable proximally / distally relative to the bushing 320.

[0023] FIG. 5 is a top view of an example of a mobile bearing prosthesis, such as prosthesis assembly 500, according to an embodiment of the present application. The prosthesis assembly 500 can be configured for implantation in a patient with a constrained knee. In an embodiment, the prosthesis assembly 500 can include a tibial baseplate 502, a tibial insert or tibial bearing component (tibial bearing component 504), and a hinge post 508.

[0024] A tibial baseplate 502 similar to the tibial baseplate 302 of FIG. 3 can be configured to be inserted into a tibia, such as the tibia 106 of the patient of FIG. 1. The tibial baseplate 502 can include a distal surface 530 (shown in FIG. 6) and a proximal surface 532. The proximal surface 532 can be on the opposite side of the distal surface 530, and the peripheral edge 534 of the tibial baseplate 502 can extend between the distal surface 530 and the proximal surface 532. The proximal surface 532 can include a recess configured to receive the hinge post 508. The proximal surface 532 can also include a first engagement mechanism 540 and a second engagement mechanism 550.

[0025] The tibial bearing component 504 can be coupled to the tibial baseplate 502, similar to the tibial bearing component 304 of FIG. 3, and can be configured to rotate about at least a first axis 542, such as an external rotation 218 about the distal axis 204 of FIG. 2. In an embodiment, the first axis 542 can extend through the centerline of the hinge post 508. The tibial bearing component 504 can include a third engagement mechanism 560 and a fourth engagement mechanism 570.

[0026] The first engagement mechanism 540 can be configured to limit rotation or movement of the tibial bearing component 504 relative to the tibial baseplate 502 about at least the first axis 542. The first engagement mechanism 540 includes a protrusion 541. The protrusion 541 can extend from the proximal surface 532 of the tibial baseplate 502. Alternatively, other embodiments of the present application contemplate that the first engagement mechanism 540 can be a slot, an opening, or other recess. In the embodiment shown in FIG. 5, the protrusion 541 can extend from the front portion of the proximal surface 532 adjacent to the peripheral edge 534 and can extend away from the distal surface 530. In another embodiment, the protrusion 541 can extend from a rear portion, an inner portion, an outer portion, or any other portion of the proximal surface 532 that can limit rotation or movement of the tibial bearing component 504 relative to the tibial baseplate 502 about at least the first axis 542. The first engagement mechanism 540 can include a first edge 544, a second edge 546, and a third edge 548.

[0027] The first edge 544 can extend rearward from the peripheral edge of the tibial base plate 502. Similarly, the second edge 546 can extend rearward from the peripheral edge of the tibial base plate 502. The third edge 548 can extend from the first edge 544 to the second edge 546. The third edge 548 can also include a concave shape 549 such that the thickness of the first engagement mechanism 540 decreases in an intermediate portion compared to the first edge 544 or the second edge 546. In an embodiment, the first edge 544 or the second edge 546 can engage with the tibial bearing component 504 to limit further rotation of the tibial bearing component 504 relative to the tibial base plate 502 about the first axis 542. The interaction between the tibial bearing component 504 and the first edge 544, the second edge 546, and the third edge 548 of the first engagement mechanism 540 will be discussed in more detail below with reference to FIGS. 7 and 8.

[0028] The third engagement mechanism 560 can be configured to engage with the first engagement mechanism 540 of the tibial bearing component 504 to at least limit rotation of the tibial bearing component 504 relative to the tibial base plate 502 about the first axis 542. The third engagement mechanism 560 can be a front recess that can include a first inner wall 562 and a second inner wall 564. For example, the third engagement mechanism 560 can be configured to contact the third edge 548 of the first engagement mechanism 540 when the tibial bearing component 504 is coupled to the tibial base plate 502. The contact between the third engagement mechanism 560 and the third edge 548 can help hold the tibial bearing component 504 on the tibial base plate 502.

[0029] The second inner wall 564 of the third engagement mechanism 560 can engage with the first edge 544. The first inner wall 562 of the third engagement mechanism 560 can engage with the second edge 546. Thus, the first inner wall 562 and the second inner wall 564 of the third engagement mechanism 560 can engage with the second edge 546 and the first edge 544, respectively, to restrict the rotation of the tibial bearing component 504 relative to the tibial base plate 502 about the first axis 542 in either the clockwise or counterclockwise direction. As shown in FIG. 5, the third engagement mechanism 560 can be formed adjacent to its peripheral edge 534 on the front portion of the tibial bearing component 504. In another embodiment, the third engagement mechanism 560 can be formed within any other portion of the tibial bearing component 504 in such a manner that the third engagement mechanism 560 can restrict the rotation of the tibial bearing component 504 relative to the tibial base plate 502 about the first axis 542. The interaction between the third engagement mechanism 560 and the first engagement mechanism 540 will be discussed in detail below with reference to FIGS. 7 and 8.

[0030] The second engagement mechanism 550 can be configured to restrict the movement of the tibial bearing component 504 relative to the tibial base plate 502 at least along the second direction 552. The movement of the tibial bearing component 504 along the second direction 552 can be restricted by the engagement between the second engagement mechanism 550 and the tibial bearing component 504. As shown in FIG. 5, the second engagement mechanism 550 can include a protrusion 551 extending from the central portion of the proximal surface 532 adjacent to, but spaced immediately behind, a recess that houses, for example, the hinge post 508. In another embodiment, the second engagement mechanism 550 can extend from behind, inside, outside, or any other portion of the proximal surface 532 in such a manner that the second engagement mechanism 550 can restrict the movement of the tibial bearing component 504 relative to the tibial base plate 502 along the second direction 552. The interaction between the tibial bearing component 504 and the second engagement mechanism 550 will be discussed in further detail below in relation to FIGS. 10 and 8.

[0031] The fourth engagement mechanism 570 may be configured to engage with the second engagement mechanism 550 of the tibial bearing component 504 to restrict movement of the tibial bearing component 504 relative to the tibial base plate 502 at least along the second direction 552. The fourth engagement mechanism 570 may be a wall of a recess formed within the tibial bearing component 504. The recess may be centrally disposed and may communicate to receive the hinge post 508 in addition to the second engagement mechanism 550. The interaction between the fourth engagement mechanism 570 and the second engagement mechanism 550 will be discussed in detail below with reference to FIGS. 10 and 8.

[0032] As shown in FIG. 5, the first engagement mechanism 540 and the second engagement mechanism 550 of the tibial base plate 502 may be protrusions, and the third engagement mechanism 560 and the fourth engagement mechanism 570 of the tibial bearing component 504 may be walls of recesses. In another embodiment, the first engagement mechanism 540 and the second engagement mechanism 550 of the tibial base plate 502 may be recesses, ridges, grooves, or any other formations formed within the surface of the tibial base plate 502, and the third engagement mechanism 560 and the fourth engagement mechanism 570 may be protrusions, ridges, extensions, or any other formations extending from the surface of the tibial bearing component 504.

[0033] FIG. 6 is a partial cross-sectional view of a constrained knee prosthesis assembly, such as the prosthesis assembly 500 taken along line 7-7 of FIG. 5, according to an embodiment of the present application. As discussed above and shown in FIG. 6, the tibial bearing component 504 may be configured to couple to the tibial base plate 502. When the tibial bearing component 504 is coupled to the tibial base plate 502, the third engagement mechanism 560 and the fourth engagement mechanism 570 of the tibial bearing component 504 may each engage with the first engagement mechanism 540 and the second engagement mechanism 550, respectively.

[0034] As shown in FIG. 6, the third engagement mechanism 560 can include a ridge that can slide under the surface of the protrusion 541 facing the distal surface 530 of the tibial baseplate 502. Similarly, the fourth engagement mechanism 570 can include a ridge that can slide under the surface of the protrusion 551 facing the distal surface 530 of the tibial baseplate 502. Thus, during the coupling of the tibial bearing component 504 to the tibial baseplate 502, the ridge of the third engagement mechanism 560 can be slid under the protrusion 541, and then the ridge of the fourth engagement mechanism 570 can be slid under the protrusion 551. During the coupling, the first engagement mechanism 540 and the second engagement mechanism 550 can be configured in a form that moves away from the hinge post 508 and bends towards the hinge post 508 to facilitate the coupling of the tibial bearing component 504 to the tibial baseplate 502. Once coupled, the protrusion 541 and the protrusion 551 engage the ridges of the third engagement mechanism 560 and the fourth engagement mechanism 570, respectively, to prevent the tibial bearing component 504 from moving relative to the tibial baseplate 502 in the second direction 552.

[0035] FIG. 7 is a top view of an example of a constrained knee prosthesis, such as the prosthesis assembly 500 including the movable bearing 704 rotated to the first set limit, according to an embodiment of the present application. Similar to the tibial bearing component 504 (see FIG. 5), the movable bearing 704 can be configured to couple with the tibial baseplate 502. As described above, the movable bearing 704 can be along the centerline of the hinge post 508 and is rotatable about at least the first axis 542. As shown in FIG. 7, the movable bearing 704 can rotate in the direction 772.

[0036] In the direction 772, the movable bearing 704 can rotate counterclockwise relative to the tibial baseplate 502 about the first axis 542. For example, the movable bearing 704 can rotate counterclockwise relative to the tibial baseplate 502 about the first axis 542 until the second inner wall 564 of the third engagement mechanism 560 contacts the first edge 544 of the first engagement mechanism 540. In such an example, the contact between the second inner wall 564 and the first edge 544 can prevent the movable bearing 704 from further rotating about the first axis 542 relative to the tibial baseplate 502. As shown in FIG. 7, the second engagement mechanism 550 engages with the fourth engagement mechanism 570, which can prevent the movable bearing 704 from further rotating about the first axis 542 relative to the tibial baseplate 502.

[0037] FIG. 8 is a top view of an example of a constrained knee prosthesis, such as a prosthesis assembly 500 including a movable bearing 704 rotated clockwise to a second set limit, according to an embodiment of the present application. The movable bearing 704 can rotate clockwise relative to the tibial baseplate 502 about the first axis 542 to any degree between the direction 772 and the direction 774. The prosthesis assembly 500 with the movable bearing 704 is typically further biased toward a neutral position between the direction 772 and the direction 774.

[0038] In the direction 774 of FIG. 7, the movable bearing 704 can rotate relative to the tibial baseplate 502 about the first axis 542. For example, the movable bearing 704 can rotate relative to the tibial baseplate 502 about the first axis 542 until the first inner wall 562 of the third engagement mechanism 560 contacts the second edge 546 of the first engagement mechanism 540. In such an example, the contact between the first inner wall 562 and the second edge 546 can prevent the movable bearing 704 from further rotating about the first axis 542 relative to the tibial baseplate 502.

[0039] FIG. 9 is a top view of an example of a constrained knee prosthesis, such as prosthesis assembly 500, including fixed bearing 904, according to an embodiment of the present application. Fixed bearing 904, such as tibial bearing component 504 (see FIG. 5), can be configured to couple with tibial base plate 502. As discussed above, fixed bearing 904 can prevent rotation or movement of fixed bearing 904 relative to tibial base plate 502 about first axis 542 and in second direction 552.

[0040] A third engagement mechanism 560 of fixed bearing 904 is configured to surround and contact first engagement mechanism 540 of tibial base plate 502 to prevent movement of fixed bearing 904 relative to tibial base plate 502 about first axis 542. For example, the recess of third engagement mechanism 560, including first inner wall 562 and second inner wall 564, along the front portion of fixed bearing 904 is smaller than the recess of third engagement mechanism 560 on movable bearing 704. Thus, first inner wall 562 and second inner wall 564 of third engagement mechanism 560 of fixed bearing 904 are configured to contact second edge 546 and first edge 544, respectively, when fixed bearing 904 is coupled to tibial base plate 502. Accordingly, first inner wall 562 and second inner wall 564 of fixed bearing 904 prevent rotation of fixed bearing 904 relative to tibial base plate 502 about first axis 542.

[0041] A fourth engagement mechanism 570 of fixed bearing 904 is configured to surround and contact second engagement mechanism 550 of tibial base plate 502 to prevent movement of fixed bearing 904 relative to tibial base plate 502 about a second axis. Fourth engagement mechanism 570 can include a flange, a protrusion, a tang, or a rib (rib 972). Rib 972 is configured to surround the opposing sides of second engagement mechanism 550 and protrusion 551 and assist in preventing rotation of fixed bearing 904 relative to tibial base plate 502 about first axis 542.

[0042] FIG. 10 is a top view of an example of a prosthesis assembly 500, including a movable bearing, such as a movable bearing 704 having a press fit 1070, according to an embodiment of the present application.

[0043] As discussed above, the prosthesis assembly 500 can be used as a movable bearing prosthesis by coupling the movable bearing 704 to the tibial base plate 502. The prosthesis assembly 500 can be used as a fixed bearing prosthesis by coupling the fixed bearing 904 to the tibial base plate 502. In another embodiment, the prosthesis assembly 500 can be made into a fixed prosthesis by using the press fit 1070. In an embodiment, the press fit 1070 can be configured to be inserted into a third engagement mechanism 560 of the movable bearing 704. In this embodiment, the press fit can be configured to fill a space between a first inner wall 562 of the third engagement mechanism 560 and a second edge 546 of the first engagement mechanism 540, and can also be configured to fill a gap between a second inner wall 564 of the third engagement mechanism 560 and a first edge 544 of the first engagement mechanism 540. Thus, the press fit 1070 can effectively change the movable bearing 704 into a fixed bearing. In this way, the movable bearing 704 can be coupled onto the tibial base plate 502, and then the press fit 1070 can be installed onto the movable bearing 704 such that the press fit engages with the third engagement mechanism 560.

[0044] As shown in FIG. 10, the first engagement mechanism 540 can include a slot extending from the peripheral portion of the movable bearing 704. The slot can receive the press fit 1070 in such a manner that the press fit 1070 slides inside the slot and surrounds the first engagement mechanism 540. In the embodiment of FIG. 10, the press fit 1070 is configured to fill the entire space between the first edge 544 of the first engagement mechanism 540 and the second inner wall 564 of the third engagement mechanism 560, and to fill the entire space between the second edge 546 of the first engagement mechanism 540 and the first inner wall 562 of the third engagement mechanism 560. In another embodiment, the press fit 1070 can be configured to fill any portion of the space between the first edge 544 of the first engagement mechanism 540 and the second inner wall 564 of the third engagement mechanism 560, and to fill the space between the second edge 546 of the first engagement mechanism 540 and the first inner wall 562 of the third engagement mechanism 560.

[0045] Additional Notes and Examples The following non-limiting examples detail some aspects of the present subject matter for solving problems and, in particular, providing the merits discussed herein.

[0046] (Example) Example 1 is a system including a constrained knee prosthesis assembly, which comprises a femoral component, a shackle component extending between a first end and a second end, a hinge shaft configured to fix the femoral component to the first end of the shackle component, a tibial baseplate having a distal surface, a proximal surface opposite to the distal surface, and a peripheral portion extending between the proximal surfaces, the tibial baseplate including a first engagement mechanism, and a hinge post extending between a first end section and a second end section, wherein the first end section is configured to be attached to the second end section of the shackle component, and the second end section is configured to be at least partially received by a recess in the tibial baseplate, a component set including the hinge post, a movable bearing coupled to the tibial baseplate and configured to rotate about at least a first axis approximated by the centerline of the hinge post, wherein the rotation about at least the first axis is restricted by at least the first engagement mechanism of the tibial baseplate, a fixed bearing configured to be coupled to the tibial baseplate and restrained from rotating about the first axis by at least the first engagement mechanism of the tibial baseplate, and the component set is configured to be assembled with either the movable bearing or the fixed bearing.

[0047] In Example 2, the subject matter of Example 1 includes that the first engagement mechanism of the tibial baseplate includes a first protrusion extending from a front portion of the proximal surface away from the distal surface.

[0048] In Example 3, the subject matter of Example 2 includes that the first protrusion includes a first edge extending rearward from the peripheral portion of the tibial baseplate, a second edge extending rearward from the peripheral portion of the tibial baseplate, and a third edge extending from the first edge to the second edge and including a concave shape.

[0049] In Example 4, the subject matter of Example 3 includes that the tibial baseplate further includes a second engagement mechanism.

[0050] In Example 5, the subject matter of Example 4 includes that the second engagement mechanism includes a second protrusion that extends from a central portion of the proximal surface and extends away from the distal surface.

[0051] In Example 6, the subject matter of Example 5 includes that the movable bearing is provided with a third engagement mechanism configured to contact a third edge of the first engagement mechanism when the movable bearing and the tibial baseplate are coupled, and the third engagement mechanism is also configured to engage with a first edge or a second edge of the first engagement mechanism when the movable bearing rotates at least about the first axis.

[0052] In Example 7, the subject matter of Example 6 includes that the engagement of the third engagement mechanism with the first edge and the second edge of the first engagement mechanism limits the rotation of the movable bearing.

[0053] In Example 8, the subject matter of Examples 6 to 7 includes that the third engagement mechanism is formed in a front portion of the movable bearing.

[0054] In Example 9, the subject matter of Examples 5 to 8 includes that the movable bearing is provided with a fourth engagement mechanism configured to engage with the second engagement mechanism of the tibial baseplate when the movable bearing rotates about a second axis relative to the tibial baseplate, and the engagement of the fourth engagement mechanism with the second engagement mechanism limits the rotation of the movable bearing about the second axis.

[0055] In Example 10, the subject matter of Example 9 includes that the fourth engagement mechanism is formed within the movable bearing adjacent to a recess configured to receive the hinge post.

[0056] In Example 11, the subject matter of Example 10 includes that the fourth engagement mechanism is located behind the recess configured to receive the hinge post.

[0057] In Example 12, the subject matter of Examples 9 to 11 includes that the rotation of the movable bearing about the second axis includes the adduction and abduction of the prosthesis assembly.

[0058] In Example 13, the subject matter of Examples 4 to 12 includes that the fixed bearing is configured to engage with the first engagement mechanism of the tibial baseplate when the fixed bearing and the tibial baseplate are coupled.

[0059] In Example 14, the subject matter of Example 13 includes that the fixed bearing includes a third engagement mechanism that contacts the first edge, the second edge, and the third edge of the first engagement mechanism to prevent the rotation of the movable bearing at least about the first axis.

[0060] In Example 15, the subject matter of Examples 13 to 14 includes that the fixed bearing includes a fourth engagement mechanism formed within the central portion of the fixed bearing, and the fourth engagement mechanism contacts the second engagement mechanism of the tibial baseplate when the fixed bearing and the tibial baseplate are coupled.

[0061] In Example 16, the subject matter of Example 15 includes that the fourth engagement mechanism includes a pair of ribs that engage with the second engagement mechanism on its opposite side.

[0062] Example 17 is a system including a constrained knee prosthesis assembly, the system comprising a tibial baseplate having a distal surface and a proximal surface opposite the distal surface and configured to receive a hinge post, the tibial baseplate including a first engagement mechanism; a movable bearing coupled to the tibial baseplate and configured to rotate about at least a first axis approximated by a centerline of the hinge post, rotation about the at least first axis being restricted by at least the first engagement mechanism; and a fixed bearing configured to be coupled to the tibial baseplate, rotation about the first axis being inhibited by at least the first engagement mechanism of the tibial baseplate. The tibial baseplate is configured to be assembled with either the movable bearing or the fixed bearing.

[0063] In Example 18, the subject matter of Example 17 includes that the first engagement mechanism of the tibial baseplate includes a first protrusion extending away from the distal surface and extending from a front portion of the proximal surface.

[0064] In Example 19, the subject matter of Example 18 includes that the first protrusion extends rearward from a peripheral edge of the tibial baseplate, the peripheral edge of the tibial baseplate including a first edge defined by the distal surface and the proximal surface of the tibial baseplate, a second edge extending rearward from the peripheral edge of the tibial baseplate, and a third edge extending from the first edge to the second edge and including a concave shape.

[0065] In Example 20, the subject matter of Example 19 includes that the tibial baseplate further includes a second engagement mechanism.

[0066] In Example 21, the subject matter of Example 20 includes that the second engagement mechanism includes a second protrusion extending from a central portion of the proximal surface and extending away from the distal surface.

[0067] In Example 22, the subject matter of Example 21 is that the movable bearing comprises a third engagement mechanism configured to contact a third edge of the first engagement mechanism when the movable bearing and the tibial baseplate are coupled, and the third engagement mechanism is also configured to engage with a first edge or a second edge of the first engagement mechanism when the movable bearing rotates at least about a first axis.

[0068] In Example 23, the subject matter of Example 22 is that the engagement of the third engagement mechanism with the first edge and the second edge of the first engagement mechanism includes restricting the rotation of the movable bearing.

[0069] In Example 24, the subject matter from Example 22 to Example 23 is that the third engagement mechanism is formed within a front portion of the movable bearing.

[0070] In Example 25, the subject matter from Example 21 to Example 24 is that the movable bearing comprises a fourth engagement mechanism configured to engage with a second engagement mechanism of the tibial baseplate when the movable bearing rotates about a second axis relative to the tibial baseplate, and the engagement of the fourth engagement mechanism with the second engagement mechanism includes restricting the rotation of the movable bearing about the second axis.

[0071] In Example 26, the subject matter of Example 25 is that the fourth engagement mechanism is formed within the movable bearing adjacent to a recess configured to receive the hinge post.

[0072] In Example 27, the subject matter of Example 26 is that the fourth engagement mechanism is behind a recess configured to receive the hinge post.

[0073] In Example 28, the subject matter from Example 25 to Example 27 is that the rotation of the movable bearing about the second axis includes internal rotation and external rotation of the prosthesis assembly.

[0074] In Example 29, the subject matter of Examples 20 to 28 includes that the fixed bearing is configured to engage with the first engagement mechanism of the tibial base plate when the fixed bearing and the tibial base plate are coupled.

[0075] In Example 30, the subject matter of Example 29 includes that the fixed bearing includes a third engagement mechanism that contacts the first edge, the second edge, and the third edge of the first engagement mechanism to prevent rotation of the movable bearing around at least the first axis.

[0076] In Example 31, the subject matter of Examples 29 to 30 includes that the fixed bearing includes a fourth engagement mechanism formed within the central portion of the fixed bearing, and the fourth engagement mechanism contacts the second engagement mechanism of the tibial base plate when the fixed bearing and the tibial base plate are coupled.

[0077] In Example 32, the subject matter of Example 31 includes that the fourth engagement mechanism includes a pair of ribs that engage with the second engagement mechanism on its opposite side.

[0078] Example 33 is an instrument comprising means for implementing any one of Examples 1 to 32.

[0079] Example 34 is a system for implementing any one of Examples 1 to 32.

[0080] Example 35 is a method for implementing any one of Examples 1 to 32.

[0081] Example 36 is a system, method, or instrument comprising any element of any one of Examples 1 to 32.

[0082] The foregoing detailed description includes references to the accompanying drawings that form a part of this detailed description. The drawings illustrate, by way of example, specific embodiments that are practicable. These embodiments are also referred to herein as "examples". Such examples may include other elements in addition to those illustrated or described. However, the inventors also contemplate examples that comprise only those elements that are illustrated or described. Further, the inventors contemplate examples using any combination or permutation of those illustrated or described (or one or more aspects thereof) with respect to a particular example (or one or more aspects thereof), or with respect to any other example (or one or more aspects thereof) illustrated or described herein.

[0083] All publications, patents, and patent documents referred to herein are incorporated herein by reference in their entirety as if each were individually incorporated by reference. In case of conflict in usage between this specification and these documents, the usage in the incorporated reference should be considered supplementary to that of this specification.

[0084] As used herein, the terms "a" or "an" are used to include one or more, regardless of any other instances or uses of "at least one" or "one or more", as is common in patent documents. In this specification, unless otherwise indicated, the term "or" is used to mean non-exclusive "or", or "A or B" is used to include "A but not B", "B but not A", and "A and B". In the appended claims, the terms "including" and "in which" are used as plain English equivalents of the terms "comprising" and "wherein", respectively. Similarly, in the following claims, the terms "including" and "comprising" are open-ended. That is, a system, device, article, or process that includes other elements in addition to those recited after such terms in the claims is still considered to be within the scope of that claim. Moreover, in the following claims, the terms "first", "second", and "third" are used merely as labels and are not intended to impose numerical requirements on their objects.

[0085] As used herein, the term "about" means approximately, in the region of, roughly or around. When the term "about" is used in conjunction with a numerical range, it modifies that range by extending the boundaries above and below the recited numerical values. Generally, the term "about" is used herein to modify a numerical value by a difference of 10% above and below the recited value. In one aspect, the term "about" means ±10% of the numerical value of the numbers with which it is used. Thus, about 50% means in the range of 45% to 55%. Numerical ranges recited herein by endpoints include all numbers and fractions subsumed within that range, e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.90, 4, 4.24 and 5. Similarly, numerical ranges recited herein by endpoints include sub-ranges subsumed within that range, e.g., 1 to 5 includes 1 to 1.5, 1.5 to 2, 2 to 2.75, 2.75 to 3, 3 to 3.90, 3.90 to 4, 4 to 4.24, 4.24 to 5, 2 to 5, 3 to 5, 1 to 4 and 2 to 4. It should also be understood that all numbers and fractions thereof are presumed to be modified by the term "about".

[0086] The above description is not intended to be limiting, but rather exemplary. For example, the above-described embodiments (or one or more aspects thereof) may be used in combination with each other. For example, other embodiments may be used by those skilled in the art upon reviewing the above description. The abstract is provided to enable the reader to quickly ascertain the content of the technical disclosure, and is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above detailed description, various features may be grouped together in order to simplify the disclosure. This should not be construed as intending that features of the disclosed subject matter not claimed are essential to any of the claims. Rather, the inventive subject matter may lie in less than all of the features of a particular disclosed embodiment. Accordingly, the following claims are incorporated into the detailed description herein, with each claim standing on its own as a separate embodiment. The scope of the embodiments must be determined with reference to the appended claims along with the full scope of equivalents to which the claims are entitled. According to aspect (1), a system comprising a prosthetic assembly for a constrained knee, a femur component, a shackle component extending between a first end and a second end, a hinge shaft configured to fix the femur component to the first end of the shackle component, a tibial baseplate having a distal surface, a proximal surface opposite the distal surface, and a peripheral portion extending between the proximal surfaces, the tibial baseplate including a first engagement mechanism, a hinge post extending between a first end section and a second end section, the first end section being configured to be attached to the second end of the shackle component, and the second end section being configured to be at least partially received by a recess in the tibial baseplate, a component set including, A movable bearing configured to be coupled to the tibial baseplate and to rotate about at least a first axis approximated by a centerline of the hinge post, wherein the rotation about at least the first axis is restricted by at least the first engagement mechanism of the tibial baseplate, and the movable bearing; A fixed bearing configured to be coupled to the tibial baseplate, wherein rotation about the first axis is inhibited by at least the first engagement mechanism of the tibial baseplate, and the fixed bearing; A system comprising: The component set is configured to be assembled with either the movable bearing or the fixed bearing. According to aspect (2), the first engagement mechanism of the tibial baseplate includes a first protrusion extending from a front portion of the proximal surface away from the distal surface. According to aspect (3), the first protrusion A first edge extending rearward from the peripheral edge of the tibial baseplate; A second edge extending rearward from the peripheral edge of the tibial baseplate; A third edge extending from the first edge to the second edge and including a concave shape; And including. According to aspect (4), the tibial baseplate further comprises a second engagement mechanism. According to aspect (5), the second engagement mechanism includes a second protrusion extending from a central portion of the proximal surface and extending away from the distal surface. According to aspect (6), the movable bearing includes a third engagement mechanism configured to contact the third edge of the first engagement mechanism when the movable bearing and the tibial baseplate are coupled, and the third engagement mechanism is also configured to engage the first edge or the second edge of the first engagement mechanism when the movable bearing rotates about at least the first axis. According to aspect (7), the engagement of the third engagement mechanism with the first edge and the second edge of the first engagement mechanism restricts the rotation of the movable bearing. According to aspect (8), the third engagement mechanism is formed within the front portion of the movable bearing. According to aspect (9), the movable bearing includes a fourth engagement mechanism configured to engage with the second engagement mechanism of the tibial baseplate when the movable bearing rotates about a second axis relative to the tibial baseplate, and the engagement of the fourth engagement mechanism with the second engagement mechanism restricts the rotation of the movable bearing about the second axis. According to aspect (10), the fourth engagement mechanism is formed within the movable bearing adjacent to a recess configured to receive the hinge post. According to aspect (11), the fourth engagement mechanism is located behind the recess configured to receive the hinge post. According to aspect (12), the rotation of the movable bearing about the second axis includes the varus and valgus rotation of the prosthesis assembly. According to aspect (13), the fixed bearing is configured to engage with the first engagement mechanism of the tibial baseplate when the fixed bearing and the tibial baseplate are coupled. According to aspect (14), the fixed bearing includes a third engagement mechanism that contacts the first edge, the second edge, and the third edge of the first engagement mechanism to prevent at least the rotation of the movable bearing about the first axis. According to aspect (15), the fixed bearing includes a fourth engagement mechanism formed within the central portion of the fixed bearing, and the fourth engagement mechanism contacts the second engagement mechanism of the tibial baseplate when the fixed bearing and the tibial baseplate are coupled. According to aspect (16), the fourth engagement mechanism includes a pair of ribs that engage with the second engagement mechanism on its opposite side. According to aspect (17), a system including a prosthesis assembly for a constrained knee, A tibial baseplate having a distal surface and a proximal surface opposite the distal surface and configured to receive a hinge post, the tibial baseplate including a first engagement mechanism, A movable bearing coupled to the tibial baseplate and configured to rotate about at least a first axis approximated by a centerline of the hinge post, wherein the rotation about at least the first axis is restricted by at least the first engagement mechanism, the movable bearing, A fixed bearing configured to be coupled to the tibial baseplate and restrained from rotating about the first axis by at least the first engagement mechanism of the tibial baseplate, the fixed bearing, A system comprising, The tibial baseplate is configured to be assembled with either the movable bearing or the fixed bearing, the system. According to aspect (18), the first engagement mechanism of the tibial baseplate includes a first protrusion extending from a front portion of the proximal surface away from the distal surface, the first protrusion being, A first edge extending rearward from a peripheral edge of the tibial baseplate, the peripheral edge of the tibial baseplate being defined by the distal surface and the proximal surface of the tibial baseplate, the first edge, A second edge extending rearward from the peripheral edge of the tibial baseplate, A third edge extending from the first edge to the second edge and including a concave shape, Including. According to aspect (19), the tibial baseplate further comprises a second engagement mechanism including a second protrusion that extends from a central portion of the proximal surface and extends away from the distal surface. The movable bearing comprises a third engagement mechanism configured to contact the third edge of the first engagement mechanism when the movable bearing and the tibial baseplate are coupled. The third engagement mechanism is also configured to engage the first edge or the second edge of the first engagement mechanism when the movable bearing rotates at least about the first axis. The engagement of the third engagement mechanism with the first edge and the second edge of the first engagement mechanism limits the rotation of the movable bearing. According to aspect (20), the movable bearing comprises a fourth engagement mechanism configured to engage the second engagement mechanism of the tibial baseplate when the movable bearing rotates about a second axis relative to the tibial baseplate. The engagement of the fourth engagement mechanism with the second engagement mechanism limits the rotation of the movable bearing about the second axis. The fourth engagement mechanism is formed within the movable bearing adjacent to a recess configured to receive the hinge post. The fourth engagement mechanism is behind the recess configured to receive the hinge post. The rotation of the movable bearing about the second axis includes varus and valgus of the prosthesis assembly.

Claims

1. A system including a prosthetic assembly for a constrained knee, a femoral component, a shackle component extending between a first end and a second end, a hinge shaft configured to fix the femoral component to the first end of the shackle component, a tibial baseplate having a distal surface, a proximal surface opposite the distal surface, and a peripheral portion extending between the proximal surfaces, the tibial baseplate including a first engagement mechanism, a hinge post extending between a first end section and a second end section, the first end section being configured to be attached to the second end of the shackle component, and the second end section being configured to be at least partially received by a recess in the tibial baseplate, a component set including, a movable bearing of a movable tibial bearing component adapted to the component set and configured to receive the hinge post, the movable bearing being coupled to the tibial baseplate and configured to rotate about at least a first axis approximated by a centerline of the hinge post, and rotation about at least the first axis being restricted by at least the first engagement mechanism of the tibial baseplate, a fixed bearing of a fixed tibial bearing component adapted to the component set and configured to receive the hinge post, the fixed bearing being configured to be coupled to the tibial baseplate and being inhibited from rotating about at least the first axis by at least the first engagement mechanism of the tibial baseplate, a system comprising, wherein the movable bearing of the movable tibial bearing component and the fixed bearing of the fixed tibial bearing component can be replaced with each other inside the prosthetic assembly.

2. The system according to claim 1, wherein the first engagement mechanism of the tibial baseplate includes a first protrusion extending from a front portion of the proximal surface away from the distal surface.

3. The first protrusion includes a first edge extending rearward from the peripheral portion of the tibial baseplate, a second edge extending rearward from the peripheral portion of the tibial base plate; a third edge extending from the first edge to the second edge and including a concave shape; The system according to claim 2, comprising:

4. The system according to claim 3, wherein the tibial base plate further comprises a second engagement mechanism.

5. The system according to claim 4, wherein the second engagement mechanism includes a second protrusion extending from a central portion of the proximal surface and extending away from the distal surface.

6. The movable bearing comprises a third engagement mechanism configured to contact the third edge of the first engagement mechanism when the movable bearing and the tibial base plate are coupled, and the third engagement mechanism is also configured to engage the first edge or the second edge of the first engagement mechanism when the movable bearing rotates at least about the first axis. The system according to claim 5.

7. The engagement of the third engagement mechanism with the first edge and the second edge of the first engagement mechanism limits the rotation of the movable bearing. The system according to claim 6.

8. The system according to claim 6, wherein the third engagement mechanism is formed in a front portion of the movable bearing.

9. The movable bearing is configured to engage the second engagement mechanism of the tibial base plate when the movable bearing moves along a second direction parallel to the first axis with respect to the tibial base plate, and the engagement of the fourth engagement mechanism with the second engagement mechanism limits the movement of the movable bearing along the second direction. The system according to claim 5.

10. The system according to claim 9, wherein the fourth engagement mechanism is formed in the movable bearing adjacent to a recess configured to receive the hinge post.

11. The system according to claim 10, wherein the fourth engagement mechanism is behind the recess configured to receive the hinge post.

12. The movement of the movable bearing along the second direction includes internal rotation and external rotation of the prosthesis assembly. The system according to claim 9.

13. The system according to claim 4, wherein the fixed bearing is configured to engage with the first engagement mechanism of the tibial base plate when the fixed bearing is coupled to the tibial base plate.

14. The system according to claim 13, wherein the fixed bearing comprises a third engagement mechanism that contacts the first edge, the second edge, and the third edge of the first engagement mechanism to prevent rotation of the movable bearing about at least the first axis.

15. The system according to claim 13, wherein the fixed bearing comprises a fourth engagement mechanism formed within a central portion of the fixed bearing, and the fourth engagement mechanism contacts the second engagement mechanism of the tibial base plate when the fixed bearing is coupled to the tibial base plate.

16. The system according to claim 15, wherein the fourth engagement mechanism includes a pair of ribs that engage the second engagement mechanism on its opposite side.

17. A system including a prosthesis assembly for a constrained knee, a tibial base plate having a distal surface and a proximal surface opposite the distal surface and configured to receive a hinge post, the tibial base plate including a first engagement mechanism, a movable bearing as a movable tibial bearing component adapted to the tibial base plate and configured to receive the hinge post, the movable bearing being coupled to the tibial base plate and configured to rotate about at least a first axis approximated by a centerline of the hinge post, and the rotation about at least the first axis being restricted by at least the first engagement mechanism, a fixed bearing as a fixed tibial bearing component adapted to the tibial base plate and configured to receive the hinge post, the fixed bearing being configured to be coupled to the tibial base plate and being inhibited from rotating about the first axis by at least the first engagement mechanism of the tibial base plate, a system comprising: The system wherein the movable bearing of the movable tibial bearing component and the fixed bearing of the fixed tibial bearing component are interchangeable with each other inside the prosthesis assembly.

18. The first engagement mechanism of the tibial base plate includes a first protrusion extending from a front portion of the proximal surface away from the distal surface, and the first protrusion is a first edge extending rearward from a peripheral portion of the tibial base plate, wherein the peripheral portion of the tibial base plate is defined by the distal surface and the proximal surface of the tibial base plate, the first edge, a second edge extending rearward from the peripheral portion of the tibial base plate, a third edge extending from the first edge to the second edge and including a concave shape, The system according to claim 17, comprising.

19. The tibial base plate further includes a second engagement mechanism including a second protrusion extending from a central portion of the proximal surface and extending away from the distal surface. The movable bearing is configured to contact the third edge of the first engagement mechanism when the movable bearing and the tibial base plate are coupled. The third engagement mechanism is also configured to engage the first edge or the second edge of the first engagement mechanism when the movable bearing rotates at least about the first axis. The engagement of the third engagement mechanism with the first edge and the second edge of the first engagement mechanism limits the rotation of the movable bearing. The system according to claim 18.

20. The movable bearing is provided with a fourth engagement mechanism configured to engage the second engagement mechanism of the tibial base plate when the movable bearing moves along a second direction parallel to the first axis with respect to the tibial base plate. The engagement of the fourth engagement mechanism and the second engagement mechanism limits the movement of the movable bearing along the second direction. The fourth engagement mechanism is formed in the movable bearing adjacent to a recess configured to receive the hinge post. The fourth engagement mechanism is behind the recess configured to receive the hinge post. The movement of the movable bearing along the second direction includes internal rotation and external rotation of the prosthesis assembly. The system according to claim 19.

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