Modular artificial knee system

Abstract

To provide artificial knee prostheses used for total artificial knee joint replacement.SOLUTION: A knee joint prosthesis moves between an extended and flexion positions. The prosthesis includes a femoral component configured to be mounted to a femur, the femoral component having a femoral gear including a plurality of posts arranged along a helical trajectory. The prosthesis also includes a tibial component configured to (i) be mounted either directly or indirectly to a tibia, and (ii) engage the femoral component. The tibial component includes a plurality of recesses that is configured to mesh with the posts of the femoral gear. A tibial gear has two intersecting portions including a horizontally oriented curved portion and a vertical portion, in which each portion includes at least one of the recesses. The plurality of posts follows the helical trajectory to cause movement of the tibial component in either a medial or lateral direction as the knee joint prosthesis is moved to the extended position.SELECTED DRAWING: Figure 8B

Description

Technical Field

[0003]

[0001] The present invention generally relates to artificial knee prostheses used for total knee arthroplasty (TKR), and more particularly to knee joint prostheses having an artificial anterior cruciate ligament (ACL) and / or a posterior cruciate ligament (PCL).

Background Art

[0002] As described in Patent Document 1 for Garino (U.S. Patent Application Publication No. 2017 / 0252173), which is hereby incorporated by reference in its entirety for all purposes, a prosthetic knee generally includes three main components: a femoral component (Figs. 1A and 1B) attached to the distal end of the femur, a tibial base plate (Figs. 2A and 2B) implanted on the proximal end of the tibia, and an artificial tibial insert (Figs. 3A and 3B) assembled on the tibial base plate and providing a friction surface for the femoral component. These components are designed to simulate the joints and associated mechanics of the human knee throughout the range of motion of the knee. The components are generally provided in various shapes with variable dimensions (identified as dimensions A-H and J-T in Figs. 1A-3B), thus allowing the physician to select an optimal combination of components according to the specific anatomy of the patient. The size and shape of the knee are influenced by various factors including the patient's age, gender, and size. Thus, generally, a fairly wide range of component lists are available, and thus the prosthetic knee can be adjusted to fit the patient.

[0003] During conventional knee reconstruction using TKR, the ACL is removed in the vast majority of cases, and depending on the design of the chosen TKR, the patient's PCL is either preserved or replaced by some mechanism to compensate for the lost function of the PCL. Even when the PCL is preserved, a portion of the PCL must be amputated or partially amputated during surgery to facilitate the equilibrium of the knee replacement. If the PCL is completely removed, it is replaced by a post-and-cam mechanism.

[0004] A TKR generally comprises a femoral component 10, a tibial baseplate 16 having a post 18 implanted within a bore formed in the tibia, and an articular insert 22 located on the apical assembly portion 20 of the tibial baseplate 16 to interface with the femoral component 10. The articular insert 22 may be separate from the tibial baseplate 16, as shown in the illustration, or it may be integrated with the tibial baseplate 16 to form a single component. The articular insert 22 and the tibial baseplate 16 may be referred to herein together or separately as the “tibial component.”

[0005] Referring to Figures 1A, 1B, 3A, and 3B, a typical design of the post-and-cam mechanism is illustrated. The joint insert 22 includes an extension 24 that protrudes into the opening 12 of the femoral component 10. A box 11 with upwardly projecting walls is formed on the interior side of the femoral component 10 and includes an internal region that intersects with the opening 12. The extension 24 includes a posterior surface 25 that is intended to be in frictional contact with the posterior surface 14 of the opening 12 when the joint is flexed. The resistance generated when the extension 24 is supported on the posterior surface 14 of the opening 12 within the femoral component 10 is intended to simulate the resistance that a healthy posterior cruciate ligament (PCL) would generate.

[0006] Cam-and-post mechanisms have been manufactured that partially replace the function of the ACL by creating a cam surface between the front surface of the extension portion 24 and the front surface of the opening 12; however, this solution only partially replaces the ACL because the front side of the extension portion 24 can only contact the front side of the opening with a bend of only about 0 to 20 degrees.

[0007] As a result of the lack of anatomically correct replacement, the functionality of the TKR may be reduced compared to the original knee. This may lead to difficulties during postoperative physical therapy and may limit the patient's ability to exercise or willingness to participate in exercise after therapy. Virtually all modern total knee arthroplasty sacrifices the ACL or improperly replaces it with a crude cam-and-post mechanism, and therefore the kinematic pattern of the reconstructed knee is left to resemble that of an ACL-deficient knee. Consequently, the kinematic pattern of a normal knee remains difficult to understand. Furthermore, the lack of proper interaction between the ACL and PCL (which jointly drive the kinematic pattern of a normal knee) means that TKR reconstructions do not even produce a relatively normal knee for the patient.

[0008] Due to the complex mechanics of the knee joint and the difficulty patients have in adapting to artificial knees postoperatively, there is a need for an anatomically correct knee replacement system that more accurately simulates the elasticity and support previously provided by the excised ligaments. To provide a more anatomically correct TKR, a prosthesis embodiment that replicates the functions provided by both the ACL and PCL is desirable.

[0009] Referring here to Figure 4, a healthy human knee is illustrated with loop 30 representing an exemplary artificial ACL / PCL ligament drawn over the original anatomical ACL and PCL locations. The division of loop 30 constituting the artificial PCL is demarcated by points 26A and 26B. The division of loop 30 constituting the artificial ACL is demarcated by points 28A and 28B.

[0010] Referring here to Figures 5, 6A, and 6B illustrating one embodiment disclosed in Patent Document 1 for Garino, the connection points 26a, 26b, 28a, and 28b of the artificial material provided as ligament 44, as well as the multiple lengths spanning between the connection points provided as the contour of the artificial ligament 44, are configured to simulate the dimensions and attachment points of the ACL and PCL within the human knee, as illustrated in Figure 4. At least one length of the artificial ligament may be provided for the purpose of connecting the TKR femoral component 10 and the joint insert 22.

[0011] While Patent Document 1 for Garino provides solutions to these complexities, further development in this field is needed to improve the mechanics of the knee joint. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] U.S. Patent Application Publication No. 2017 / 0252173 [Overview of the project]

[0013] In one embodiment of the present invention, a knee joint prosthesis is configured to move between an extension position and a flexion position. The prosthesis includes a femoral component configured to be attached to a femur, the femoral component having a femoral gear including a plurality of conical posts arranged along a helical trajectory. The prosthesis also includes a tibia configured to (i) be attached directly or indirectly to the tibia and (ii) engage with the femoral component. The tibial component includes a plurality of recesses configured to mesh with the conical posts of the femoral gear. The tibial gear has two intersecting portions, including a horizontally oriented curved portion and a vertical portion, each portion including at least one of the recesses. The plurality of conical posts follow a helical trajectory, causing the tibial component to move in either a medial or lateral direction as the knee joint prosthesis is moved to the extension position. [Brief explanation of the drawing]

[0014] [Figure 1A] Figure 1A is a side view of a femoral component for a knee joint prosthesis, which is known to those skilled in the art. [Figure 1B] Figure 1B is a bottom view of the femoral component shown in Figure 1A. [Figure 2A] Figure 2A is a top view of a tibial component for a knee joint prosthesis, which is known to those skilled in the art. [Figure 2B] Figure 2B is a lateral view of the tibial component shown in Figure 2A. [Figure 3A] Figure 3A is a top view of a joint insert for a knee joint prosthesis, which is known to those skilled in the art. [Figure 3B] Figure 3B is a front view of the joint insert of Figure 3B, assembled on the base plate of the tibial component. [Figure 4] Figure 4 is a lateral view of the knee joint illustrating the anatomical locations of the ACL and PCL and the composition of prosthetic materials intended to replace the ACL and PCL. [Figure 5]Figure 5 is a side view of a femur component, an articular insert, and an artificial ligament for a TKR according to the prior art. [Figure 6A] Figure 6A is a top view of a cross-section along line I-I of Figure 5. [Figure 6B] Figure 6B is a bottom view of a cross-section along line I-I of Figure 5. [Figure 7A] Figure 7A is an assembled view of a modular knee joint prosthesis as seen from the top side, left side, and rear side according to the first embodiment. [Figure 7B] Figure 7B is an exploded assembled view of the modular knee joint prosthesis of Figure 7A. [Figure 7C] Figure 7C is a side elevation view of the modular knee joint prosthesis of Figure 7A. [Figure 7D] Figure 7D is a top plan view of the modular knee joint prosthesis of Figure 7A. [[ID={19]] [Figure 7E] Figure 7E is a rear / back elevation view of the modular knee joint prosthesis of Figure 7A. [Figure 7F] Figure 7F is a front / front elevation view of the modular knee joint prosthesis of Figure 7A. [Figure 7G] Figure 7G depicts a cross-sectional view of the modular knee joint prosthesis of Figure 7F cut along line 7G-7G, where the modular knee joint prosthesis is shown in the extended position. [Figure 7H] Figure 7H depicts another cross-sectional view of the modular knee joint prosthesis, which is the same as Figure 7G but the modular knee joint prosthesis is shown in the flexed position. [Figure 8A] Figure 8A is an assembled view of a modular knee joint prosthesis according to the second embodiment. [Figure 8B] Figure 8B is an exploded assembled view of the modular knee joint prosthesis of Figure 8A. [Figure 8C] Figure 8C is a side elevation view of the modular knee joint prosthesis of Figure 8A. [Figure 8D] Figure 8D is a top plan view of the modular knee joint prosthesis of Figure 8A. [Figure 8E] Figure 8E is a posterior / posterior elevation view of the modular knee joint prosthesis shown in Figure 8A. [Figure 8F] Figure 8F is an anterior / front elevation view of the modular knee joint prosthesis shown in Figure 8A. [Figure 8G] Figure 8G shows a cross-sectional view of the modular knee joint prosthesis shown in Figure 8F, cut along line 8G-8G, where the modular knee joint prosthesis is shown in the extended position. [Figure 8H] Figure 8H is similar to Figure 8G, but shows another cross-sectional view of the modular knee joint prosthesis, this time in a flexed position. [Figure 8I] Figure 8I shows the disassembled and assembled modular knee joint prosthesis shown in Figure 8A, in addition to the femur, tibia, and tibial baseplate. [Modes for carrying out the invention]

[0015] The present invention provides various embodiments of knee joint prostheses. In the figures, "A" represents the anterior side or direction, "P" represents the posterior side or direction, "M" represents the medial side or direction, and "L" represents the lateral side or direction.

[0016] As described in U.S. Patent No. 11,419,731 to Garino, Figures 7A–7H depict a modular knee joint prosthesis 700 according to the first embodiment. Although the following description shows and explains the prosthesis 700 for the left knee, the right knee prosthesis is substantially similar, and it should be understood that the following description also applies to the right knee prosthesis.

[0017] The prosthesis 700 generally includes a modular femoral component 702, a femoral insert 705 configured to be assembled to the femoral component 702, a modular articular component 704, and a tibial insert 706 configured to be assembled to the articular component 704.

[0018] The modular femoral component 702 includes a U-shaped body having opposing condyles 710. As is known in the art, a pin 711 extends upward from the internal surface of the component 702 for implantation of the femoral component 702 into the femur. A rectangular cutout 712 is defined within the femoral component 702 at a central location between the condyles 710. The cutout 712 extends in a posterior-anterior direction and in the sagittal plane. The cutout 712 includes an opening on the posterior side of the component 702. The cutout 712 extends through the entire wall thickness of the component 702. The cutout 712 includes three interconnected internal opposing sides: an lateral side extending in the sagittal plane, an internal side extending in the sagittal plane, and an anterior side connecting the lateral and internal sides. The posterior side of the cutout 712 is open to accommodate an insert 705.

[0019] Reliefs are formed on each of the opposing medial and lateral surfaces of the cutout 712. Together, these reliefs form a slot or track 713 configured to accommodate a rail 715 (i.e., a shoulder) formed on the opposing side of the femoral insert 705, such that the insert 705 can be placed on component 702. It should be understood that to achieve either the same or similar result, the track 713 may be placed on the insert 705, or the rail 715 on component 702.

[0020] It should be understood that, in addition to the track 713 and rail 715, the component 702 may also be provided with means for assembling the insert 705. The means for assembling may alternatively include slots, guides, rails, snap mechanisms, friction fits, interlocking fits, fasteners (screws, bolts, nuts), welding, adhesives, dovetail joints (or other interlocking surfaces).

[0021] The modular joint component 704 is configured to interface with the femoral component 702 and to reside on the apical mounting portion of the tibial component (not shown). The joint component 704 is configured to be mounted to a tibial baseplate 16 (see Figures 2B and 5), which is fixedly mounted to the tibia. Alternatively, although not shown, the joint component 704 may be integrated with the tibial baseplate 16 to form a single, standalone tibial component that is fixedly mounted to the tibia. Thus, the “tibial component” may include either the joint component 704 (alone) or both the joint component 704 and the tibial baseplate 16.

[0022] The joint component 704 includes two concave surfaces 721 for physically engaging with the convex condyle 710 of the femoral component 702 as the prosthesis 700 is moved between a flexed position and an extended position. A rectangular cutout 723 is defined in the joint component 704 at a central location between the concave surfaces 721. The cutout 723 extends in a posterior-anterior direction and in the sagittal plane. The cutout 723 includes an opening on the posterior side of the joint component 704. The cutout 723 extends through the wall thickness of the joint component 704. The cutout 723 includes three interconnected internal opposing sides: a lateral side extending in the sagittal plane, a medial side extending in the sagittal plane, and an anterior side connecting the lateral and medial sides. Reliefs are formed on each of the opposing medial and lateral sides of the cutout 723. Together, these reliefs form a slot or track 724 configured to accommodate a rail 725 (shoulder) formed on the opposite side of the tibial insert 706, such that the insert 706 can be installed on the joint component 704 by sliding the rail 725 along the track 724. It should be understood that to achieve either the same or similar result, the track 724 may be positioned on the insert 706, while the rail 725 may be positioned on the component 704.

[0023] It should be understood that, in addition to the track 724 and rail 725, means for assembling the insert 706 to the articulated component 704 may be provided. The means for assembling may alternatively include slots, guides, rails, snap mechanisms, friction fits, interference fits, fasteners (screws, bolts, nuts), welding, adhesives, dovetail joints (or other interlocking surfaces).

[0024] The femoral component 702 and the joint component 704 are modular components common to the first through fourth embodiments. The femoral component 702 and the joint component 704 may together form a modular subassembly.

[0025] Now, looking at components that can be selectively placed on these modular components 702 and 704, the femoral insert 705 is configured to be attached to the femoral component 702, and the tibial insert 706 is configured to be attached to the joint component 704 (also referred to as the tibial component 704). The femoral insert 705 and the tibial insert 706 work together to guide the movement of the prosthesis 700 between the flexion and extension positions shown in Figures 7G and 7H.

[0026] The femoral insert 705 includes an L-shaped body. The body defines an elongated horizontal portion 731, over which rails 715 protrude from its opposing lateral surfaces. The horizontal portion 731 is sized to fit snugly into the cutout 712 of the femoral component 702. A vertical portion 733 of the body extends perpendicularly from the horizontal portion 731. In the assembled form, the vertical portion 733 is flush with the condyles 710 of the femoral component 702 and bridges these condyles. The vertical portion 733 also functions as a finger tab to facilitate manual insertion and / or removal of the insert 705 onto / from the femoral component 702. The femoral insert 705 may be coupled to the femoral component 702 in either a releasable or non-releasable form.

[0027] A gear 734, shaped like a convex surface, protrudes outward from the opposing front and rear external surfaces of the L-shaped body of the insert 705. The gear 734 includes a plurality of individual gear teeth with rounded external surfaces. The gear teeth are evenly spaced along the outer circumference of the gear 734. The gear 734 follows a helical path, as can be seen in Figures 7D and 7E. Specifically, the gear 734 curves around (i) a specific axis 740 extending in the inward-outward direction (Figures 7G and 7H), and (ii) an axis extending in the front-rear direction (see Figure 7E). In other words, the gear 734 curves along two different axes oriented orthogonally to each other. The gear 734 is located on the front and rear surfaces of the L-shaped body, while the rail 715 is located on the left and right sides of the body, with its top and rear opposing surfaces being planar. The femoral insert 705 may be a single monolithic component.

[0028] The tibial insert 706 includes an elongated rectangular body. Rails 725 extend in anterior-posterior direction and protrude from opposing lateral surfaces of the body. As described above, rails 725 are sized to fit within tracks 724 formed on the articular component 704, so that rails 725 slide within their corresponding tracks 724. To facilitate manual handling of the insert 706, finger tabs 744 are defined on the lower posterior edge of the insert 706. The tibial insert 706 may be connected to the articular component 704 in either a releasable or non-releasable manner.

[0029] A curved channel 750 extends from front to rear through the body of the insert 706. The channel 750 has opposing curved side walls facing each other. The channel 750 is curved about a vertical axis (in the top-to-bottom direction or along the sagittal plane), as shown, for example, in Figure 7B. The base surface of the channel 750 has a series of gear teeth 752 extending upward from there to mesh with the teeth of the gear 734. The base surface may be flat (except for the teeth 752), or the base surface may be curved about an axis 740 (Figure 7H). The insert 706 may be a single monolithic component.

[0030] Now, looking at Figures 7G and 7H, the gear teeth 752 on the joint component 704 mesh with the gear teeth 734 on the femoral component 702, causing the joint component 704 to rotate on the femoral component 702, and vice versa. As the femoral component 702 rotates posteriorly (as indicated by the arrow) to the flexion position shown in Figure 7H, the meshed teeth pass each other and do not slide. The slight rotation of the joint component 704 in the medial-lateral direction as the prosthesis 700 moves between the flexion and extension positions is a result of the curvature of the gear teeth 734 in the medial-lateral direction, which replicates the slight rotation experienced in a real knee joint.

[0031] Figures 8A-8H depict the modular knee joint prosthesis 800 according to the second embodiment. It should be understood that prosthesis 800 is similar to prosthesis 700, and only the main differences between them are described below. Therefore, the details provided above regarding prosthesis 700 also apply to prosthesis 800 unless otherwise stated below.

[0032] The prosthesis 800 includes a femoral component 802, an articular component 804, a femoral insert 805 (also referred herein as a femoral gear), and a tibial insert 806 (also referred herein as a tibial gear). Figure 8I shows an exploded view of the prosthesis 800, in addition to the femur 850, tibia 852, and a tibial baseplate 854 (similar to baseplate 16) for use with the prosthesis 800. The tibial baseplate 854 may also be considered to be part of the prosthesis 800.

[0033] The femoral component 802 is similar to the femoral component 702, except that it includes a vertical lateral wall 803 extending above the track 813. Similarly, the articular component 804 is similar to the articular component 704, except that instead of a track (similar to the track 724), it includes a rectangular recess 824 on its bottom surface. In the assembled form, opposing tabs 825 on the tibial insert 806, which extend in a lateral-medial direction, are inserted into the recess 824, thereby capturing the articular component 804 in the tibial insert 806.

[0034] Now, looking at the femoral insert 805, the insert 805 includes a hollow cylindrical body. Rails 815 extending in the posterior-anterior direction are positioned on the opposing planar side walls of the body to engage with the track 813 of the femoral component 802. In the assembled form, the planar side walls of the body are supported and constrained in the medial-lateral direction by the side walls 803 of the femoral component 802, as shown in Figure 8A. A series of gear teeth in the form of pegs 834 are positioned on the rounded posterior surface of the insert 805. Each peg 834 has a frustoconical shape, as shown. Alternatively, each peg 834 could have a cylindrical, triangular, conical, rectangular, or trapezoidal shape (e.g., when viewed in cross-section). The free end surface of such a cylindrical peg could be flat or rounded. However, during testing, it was found that the frustoconical pegs 834 performed exceptionally well in terms of smooth movement. As shown in Figure 8E, the peg 834 may be positioned along a spiral path to replicate knee movement (as described above with respect to prosthesis 700). The spiral path is curved and drives rotation around the medial condyle as the knee flexes, forcing more translation of the lateral condyle. Alternatively, the peg 834 may be positioned along a straight path.

[0035] The pegs 834 may be spaced evenly or unevenly. For example, to enhance the stability of the prosthesis, adjacent pegs 834 that are active (i.e., engaged) at the deep flexion position of the prosthesis 800 (Figure 8H) may be positioned closer together than adjacent pegs 834 that are active at the extended position of the prosthesis 800 (Figure 8G). Similarly, the protruding length, thickness, width, etc., of each peg 834 may be uniform or uneven. Specifically, adjacent pegs 834 that are active (i.e., engaged) at the deep flexion position of the prosthesis 800 (Figure 8H) may have different protruding lengths, thicknesses, widths, etc., compared to adjacent pegs 834 that are active at the extended position of the prosthesis 800 (Figure 8G).

[0036] Now, turning to the tibial insert 806, the insert 806 comprises a substantially L-shaped body including a horizontally oriented curved portion 817 and a substantially vertical portion 819. The curvature of the horizontally oriented curved portion 817 may match the curvature of the curved surface of the femoral insert 805. The vertical portion 819 extends downward. The vertical portion 819 is provided in such a shape that the femoral insert can engage with the tibial insert at a position far posterior in the deep flexion position shown in Figure 8H, and even slightly below the posterior surface of the tibia.

[0037] In its assembled state, the vertical portion 819 passes through a rectangular channel 855 (Figure 8I) formed within the tibial baseplate 854. A series of recessed depressions 820 are formed on the outer surface of the insert 806. The outer circumference of each depression 820 is substantially circular, except for depression 821, which has a teardrop-shaped outer circumference. The circumferential shape of depression 821 can similarly be described as elliptical. Depression 821 is formed at the intersection of portions 817 and 819. Depressions 820 / 821 may be arranged along a spiral path, as shown in Figures 8B and 8E, to replicate the movement of the knee (as described above). Alternatively, depressions 820 / 821 may be arranged along a straight path. Although it has been found that the circular / elliptical shape of the depression generates the smooth kinematic behavior of prosthesis 800, it should be understood that the outer circumference of the depression 820 / 821 can be changed, and may take the shape of a rectangle, triangle, or trapezoid, for example.

[0038] It should be understood that the placement of the peg and the recess may be reversed. In other words, the peg 834 may be placed on the tibial insert 806, and the recess 820 may be placed on the femoral insert 805.

[0039] The prosthesis 800 includes access openings in the tibial and femoral components, such as the openings represented by items 712 and 723, which allow surgeons to access the intramedullary rod in case of fracture.

[0040] Although the femoral insert 805 is shown as a separate component, it may be formed as a standalone component together with the femoral component 802. Similarly, although the tibial insert 806 is shown as a separate component, it may be formed as a standalone component together with either the joint component 804 or the tibial baseplate 854.

[0041] The geometry of the femoral and tibial inserts may vary. If desired, multiple different femoral and tibial inserts can be provided as a single kit, along with one femoral component 802 and one joint component 804. When used, the surgeon can select different femoral and tibial inserts based on various factors, including, for example, the patient's age, sex, disease, and size.

[0042] The components of a knee joint prosthesis may be manufactured from the same or similar materials. However, generally speaking, all materials are preferably inert, less likely to cause infection, and otherwise safe and approved for use as a surgical implant. Exemplary materials include polyethylene, surgically approved metal alloys, surgically approved ceramic materials, or combinations thereof. Any of the various embodiments or parts thereof of the present invention may be manufactured using any material well known in the field of surgical implants.

[0043] While preferred embodiments of the present invention have been illustrated and described herein, it will be understood that such embodiments are provided merely as examples. Those skilled in the art will recognize numerous variations, modifications, and substitutions without departing from the spirit of the invention. Accordingly, the appended claims are intended to cover all such variations that fall within the spirit and scope of the invention.

Claims

1. In a knee joint prosthesis configured to move between an extended position and a flexed position, the knee joint prosthesis is: A femoral component configured to be attached to a femur, having a femoral gear including a plurality of posts arranged along a helical trajectory; and (i) a tibial component configured to be directly or indirectly attached to the tibia and (ii) to engage with the femoral component, the tibial component having a tibial gear comprising a plurality of recesses configured to mesh with the post of the femoral gear, wherein the tibial gear has two intersecting portions, comprising a horizontally oriented curved portion and a vertical portion, each portion comprising at least one of the recesses; A knee joint prosthesis including, As the plurality of posts move along a spiral trajectory, causing the knee joint prosthesis to move to the extended position, the tibial component moves in either a medial or lateral direction. Knee joint prosthesis.

2. The knee joint prosthesis according to claim 1, wherein the femoral gear and the tibial gear are configured to interlock together in both the extension and flexion positions.

3. The knee joint prosthesis according to claim 1, wherein the plurality of depressions similarly cause the tibial component to move in a helical trajectory in the medial or lateral direction as the knee joint prosthesis is moved to the extended position.

4. The knee joint prosthesis according to claim 1, wherein the knee joint prosthesis is a modular knee joint prosthesis, the femoral gear is a femoral insert removablely assembled into a first cutout or opening defined within the central region of the femoral component, and the tibial gear is a tibial insert removablely assembled into a second cutout or opening defined within the central region of the tibial component.

5. The knee joint prosthesis according to claim 4, wherein the femoral insert is removably assembled to the interior of the first cutout or opening of the femoral component by rail and slot engagement.

6. A kit comprising the knee joint prosthesis according to claim 4, a plurality of different femoral gears, and a plurality of different tibial gears.

7. The knee joint prosthesis according to claim 1, wherein the femoral gear and the femoral component are formed as a single component.

8. The knee joint prosthesis according to claim 1, wherein the tibial gear and the tibial component are formed as a single component.

9. The knee joint prosthesis according to claim 1, wherein the tibial component is a joint component having a concave seat surface shaped to engage with a condyle on the femoral component.

10. The knee joint prosthesis according to claim 1, wherein the tibial component is a tibial base plate configured to be directly attached to the tibia.

11. The knee joint prosthesis according to claim 1, wherein the femoral component includes opposing condyles, and the femoral gear and tibial gear are positioned medially-laterally at one location between the opposing condyles.

12. The knee joint prosthesis according to claim 1, wherein each of the posts has a conical or truncated cone shape.

13. The knee joint prosthesis according to claim 1, wherein the post has a different shape and the recess has a different shape.

14. The knee joint prosthesis according to claim 1, wherein the posts are unevenly spaced.

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