GB2512609A

GB2512609A - Total knee replacement prosthesis assembly

Info

Publication number: GB2512609A
Application number: GB1306003.3A
Authority: GB
Inventors: Noel Fitzpatrick; Jayantilal Mohanlal Meswania
Original assignee: Fitzbionics Ltd
Current assignee: Fitzbionics Ltd
Priority date: 2013-04-03
Filing date: 2013-04-03
Publication date: 2014-10-08
Also published as: WO2014162136A1; GB201306003D0

Abstract

A total knee replacement prosthesis assembly comprising a femoral component 20 and a tibial component. In one embodiment the tibial component comprises a tibial platform and a bearing component 40 between the femoral component and the tibial platform. The bearing can rotate relative to the tibial platform. The superior surface of the tibial platform has an abutment (35, see figure 9) extending away from it, to limit rotation of the bearing component. The posterior face of the abutment may be planar. The inferior surface of the bearing component may have a recess to receive the abutment, having two angled surfaces (43a, 43b, see figure 8) to limit rotation. The tibial component and femoral component may each have a stop to prevent hyperextension of the joint (27, 54, see figure 6). The condyles and the condyle depressions 53 may be curved only in the sagittal plane. The tibial stem (34, see figure 2) may be medially offset compared to the tibial platform 32.

Description

Total Knee Replacement Prosthesis Assembly

Field of the Invention

The invention relates to a total knee replacement (TKR) prosthesis assembly for replacement of a knee joint.

Background to the Invention

The knee joint is made up of the distal end of the femur, which articulates with the proximal end of the tibia, and the patella, which slides in a groove on the femur.

Ligaments attach the femur and tibia to provide stability.

The tibiofemoral joint at the knee in humans and animals allows for flexion (bending movement that decreases the angle between the femur and tibia) and extension (straightening movement). In addition to flexion and extension, motion of the knee is both rotational and translational. The temoral condyles both roll and glide as they articulate with respect to the tibial plateaus. The tibiofemoral joint has a screw-home' mechanism wherein during knee extension the tibia rotates externally, and this motion is reversed when the knee flexes, providing external and internal rotation within the knee joint.

In humans, knee joint replacements are commonly used for treatment of a variety of clinical conditions and there are a large number of designs to choose from. This is not true for the treatment of canine or feline populations where in the majority of cases euthanasia is usually a solution and for a few where there are a limited number of designs in the market that are available, these all have a very limited application and clinical function. In contrast to human applications the usage and loadings in four legged animals are considerably different, thus requiring a different approach to knee joint replacement. There is a need for a knee joint replacement prosthesis that is suitable for use in quadrupeds, wherein the requirements are different from those for bipeds. Features of such a knee joint replacement prosthesis may of course be suitable for knee joint replacement in a biped also.

Summary of Invention

According to a first aspect of the invention there is provided a total knee replacement prosthesis assembly comprising a femoral component and a tibial component, the tibial component comprising a tibial platform and a bearing component adapted to be arranged between the femoral component and tibial platform when assembled, the bearing component being rotatable relative to the tibial platform when assembled, wherein the tibial platform has a superior surface that faces the bearing component when assembled and an inferior surface for facing a tibia when implanted, the superior surface of the tibial platform having an abutment extending away from it, to limit the amount by which the bearing component can rotate relative to the bearing component in use.

The abutment imposes limits for rotation of the bearing component relative to the tibial platform, thus stabilising the knee joint prosthesis. The abutment is adapted such that some rotation of the bearing component relative to the tibial platform is accommodated in either direction (too allow for external and internal rotation), within the limits imposed by the abutment. At the limit of rotation either way a portion of the bearing component will abut the abutment, thus preventing further rotation. The abutment is preferably at or near the anterior edge of the tibial platform. The abutment extends substantially along a medial-lateral axis of the tibial platform. Preferably there is no abutment on the medial, lateral or posterior side of the tibial component. The assembly provides a semi-constrained knee joint replacement prosthesis assembly. Suitably the tibial platform is adapted for implantation on a subject's tibial plateau, Preferably the abutment has a posterior face for facing substantially posteriorly when implanted, the posterior face being planar.

Preferably the bearing component has a superior surface and an inferior surface, the inferior surface of the bearing component having an abutment recess for receiving the abutment when assembled. The abutment recess is preferably disposed in the anterior side of the inferior surface of the bearing component.

Preferably the abutment recess has first and second faces for facing towards the posterior face of the abutment when assembled, the first and second faces slanting relative to one another. Preferably each of first and second faces is planar.

Preferably each of the first and second faces extends from a respective first and second side edge of the bearing component to a line substantially at a mid-point between the medial and lateral sides ot the bearing component, the first and second faces each slanting in an anterior direction from the respective side edge to said line substantially at the mid-point between the medial and lateral sides of the bearing component. When the limit of rotation is reached in a first direction, the first face will abut the abutment and when the limit of rotation is reached in a second direction, the second face will abut the abutment. This allows the bearing component to rotate by a few degrees each way relative to the tibial platform (exterior and anterior rotation).

According to a second aspect of the invention there is provided a total knee replacement prosthesis assembly comprising a femoral component and a tibial component, wherein the tibial component has a projecting stop element, the femoral component having a corresponding stop element recess for engaging with the stop element to prevent hyperextension of the joint.

Preferably the femoral component has a condylar portion and a patellar portion, each having an external surface, the stop element recess being between the condylar portion and a patellar portion.

Preferably the stop element recess is an elongate groove, extending substantially along a medial-lateral axis of the femoral component. The stop element recess preferably comprises first and second portions, one on either side of the opening to a patellar track in the femoral component Preferably the stop element is an elongate protrusion extending substantially along a medial-lateral axis of the femoral component. The elongate stop element is preferably convexly curved in the sagittal plane. The elongate groove or groove portions of the stop element recess is/are preferably concavely curved in the sagittal plane.

Preferably the condylar portion comprises a pair of laterally spaced apart condyles.

The condyles are suitably parallel with one another.

Preferably the patellar portion comprises a patellar track which is shaped to conform with a natural or prosthetic patella.

According to a third aspect of the invention there is provided a total knee replacement prosthesis assembly comprising a femoral component and a tibial component, wherein the femoral component has a pair of condyles and the tibial component has a corresponding pair of condyle depressions for receiving the respective condyles of the femoral component, each of the condyles being convexly curved in the sagittal plane and each of the condyle depressions being concavely curved in the sagittal plane, the radius of curvature of each condyle substantially matching the radius of curvature of the corresponding condyle depression. The conforming surfaces of the condyles and corresponding condyle depressions provides congruent articulation, allowing for substantially unbroken contact between the femoral component and tibial component during extension and flexion of the joint.

Preferably the condyle depressions are curved in the sagittal plane only. In other words the condyle depressions are not curved in the coronal plane.

Preferably the condyles are curved in the sagittal plane only. In other words the condyles are not curved in the coronal plane.

Preferably the condyles and condyle depressions each have a substantially constant radius of curvature in the sagittal plane.

According to a fourth aspect of the invention there is provided a total knee replacement prosthesis assembly comprising a femoral component and a tibial component, the tibial component having a tibial platform adapted for implantation on a subject's tibial plateau, the tibial platform having a tibial stem adapted to be received by an intramedullary canal of a tibia bone, wherein the tibial stem extends from a point on the tibial platform that is offset medially from a notional mid point between the medial and lateral sides of the tibial platform. The medial offset of the tibial stem puts the tibial stem in the optimal location relative to the tibial plateau for implantation into the intramedullary canal of the tibia in a quadruped such as a canine. Different tibial platforms will be provided for replacement of a right knee joint and a left knee joint, with the tibial platform for a right knee joint being a mirror image in the sagittal plan of that for a left knee joint Preferred features of all of the above aspects of the invention will now be described.

Preferably tibial component comprises a tibial platform and a bearing component adapted to be arranged between the femoral component and the tibial platform when assembled. The tibial platform is adapted for implantation on a subject's tibial plateau Preferably the assembly further comprises a projection and a corresponding projection recess for receiving the projection when assembled, the projection extending away from the tibial platform or the bearing component and the recess being disposed in the other of the tibial platform or bearing component. The projection is preferably a substantially cylindrical projection, referred to herein as a post. The post couples the bearing component to the tibial platform, allowing rotation of the bearing component relative to the tibial platform, about the post's axis. The end of the projection furthest from the tibial platform or the bearing component from which it extends is preferably convexly curved. The projection recess preferably has a blind end, the blind end preferably being concavely curved, to conform with the convexly curved end of the projection. Preferably the projection extends away from the tibial platform and is received in a corresponding projection recess in the bearing component when assembled.

Preferably the assembly further comprises an intercondylar projection extending from a superior surface of the tibial component, the femoral component having a corresponding intercondylar recess for receiving the intercondylar projection.

Preferably the tibial component comprises a tibial platform and a bearing component adapted to be arranged between the femoral component and the tibial platform when assembled and the intercondylar projection extends from a superior surface of the bearing component. Preferably the intercondylar projection is convexly curved in the sagittal plane. Preferably the intercondylar projection is curved in the sagittal plane only. In other words the intercondylar projection is not curved in the coronal plane.

Preferably the intercondylar projection has side surfaces which are substantially flat and parallel.

Preferably the femoral component has a femoral stem adapted to be received by an intramedullary canal of a femur bone, Preferably the tibial component comprises a tibial platform and a bearing component adapted to be arranged between the femoral component and tibial platform when assembled, wherein the tibial platform has a superior surface that faces the bearing component when assembled and an inferior surface for facing a tibia when implanted, the superior surface of the tibial platform having an abutment extending away from it, to limit the amount by which the bearing component can rotate relative to the bearing component in use. Preferably the abutment has a posterior face for facing substantially posteriorly when implanted, the posterior face being planar. Preferably the bearing component has a superior surface and an inferior surface, the inferior surface of the bearing component having an abutment recess for receiving the abutment. Preferably the abutment recess has first and second faces for facing towards the posterior face of the abutment when assembled, the first and second faces slanting relative to one another. Preferably each of the first and second faces extends from a respective first and second side edge of the bearing component to a line substantially at a mid-point between the medial and lateral sides of the bearing component, the first and second faces each slanting in an anterior direction from the respective side edge to said line substantially at the mid-point between the medial and lateral sides of the bearing component.

Preferably the tibial component has a projecting stop element, the femoral component having a corresponding stop element recess for engaging with the stop element to prevent hyperextension of the joint. Preferably the tibial component comprises a tibial platform and a bearing component adapted to be arranged between the femoral component and the tibial component when assembled, the stop element projecting from the bearing component. Preferably the femoral component has a condylar portion and a patellar portion, each having an external surface, the stop element recess being between the condylar portion and a patellar portion. Preferably the stop element recess is an elongate groove, extending substantially along a medial-lateral axis of the femoral component. Preferably the stop element is an elongate protrusion extending substantially along a medial-lateral axis of the femoral component. Preferably the condylar portion comprises a pail of laterally spaced apart condyles. Preferably the patellar portion comprises a patellar track which is shaped to conform with a natural or prosthetic patella. Preferably the stop element is convexly curved in a plane perpendicular to its longitudinal axis. Preferably the stop element recess is correspondingly concavely curved in a plane perpendicular to its longitudinal axis, such that it is adapted to receive the stop element. Preferably the stop element recess comprises first and second stop element recess portions separated by a channel therebetween. The channel is the opening to the patellar track in the femoral component.

Preferably the femoral component has a pair of condyles and the tibial component has a corresponding pair of condyle depressions for receiving the respective condyles of the femoral component, each of the condyles being convexly curved in the sagittal plane and each of the condyle depressions being concavely curved in the sagittal plane, the radius of curvature of each condyle substantially matching the radius of curvature of the corresponding condyle depression. Preferably the condyle depressions are curved in the sagittal plane only. Preferably the condyles are curved in the sagittal plane only. Preferably the condyles and condyle depressions each have a substantially constant radius of curvature in the sagittal plane.

Preferably the tibial component has a tibial platform adapted for implantation on a subject's tibial plateau, the tibial platform having a tibial stem adapted to be received by an intremedullary canal of a tibia bone, wherein the tibial stem extends from a point on the tibial platform that is offset medially from a notional mid point between the medial and lateral sides of the tibial platform.

Human anatomical terms such as posterior, anterior, superior, inferior have been used herein, however these are relative terms and it will be understood that these terms can be substituted with the corresponding zootomical terms relevant to the anatomy of a four-legged animal. Anatomical directional terms have been used herein in relation to the parts of the prosthesis assembly. Such terms correspond to the directions relative to a subject when the assembly is implanted in a subject, however it will be understood that these terms are used to provide a frame of reference and apply to the assembly whether it is implanted or is outside of the body of a subject.

The term subject as used herein can be a human or animal subject.

Brief Description of the Drawings

A preferred embodiment of the present invention will now be more particularly described by way of example only with reference to the accompanying drawings, wherein: Figure 1 is a lateral side view of an assembled total knee replacement prosthesis assembly according to the invention, with the prosthesis assembly shown in an extended configuration; Figure 2 is an anterior view of the assembly of Figure 1 Figure 3 is a side view of the assembly of Figure 1, but with the assembly shown in a flexed configuration; Figure 4 is an exploded perspective view of the components of the assembly of Figure 1; Figure 5A is an exploded perspective view of the femoral component and bearing component; Figure 5B is a perspective view of the femoral component; Figure 6 is a close-up lateral side view of the femoral component and bearing component of the assembly of Figure 1, shown in the extended configuration; Figure 7 is a perspective view of the assembly of Figure 1, with the assembly shown in a flexed configuration; Figure 8 is an underside perspective view of the bearing component of the assembly of Figure 1; Figure 9 is a perspective view of the tibial platform of the assembly of Figure 1; Figure 10 is a side perspective view of the bearing component and tibial platform of the assembly of Figure 1 assembled together; Figure 11 is an underside perspective view of the tibial platform with stem of the assembly of Figure 1; Figure 12 is a top perspective view of the tibial platform with stem of the assembly of Figure 1.

Description of the Preferred Embodiments

The present embodiments represent currently the best ways known to the applicant of putting the invention into practice. But they aie not the only ways in which this can be achieved. They are illustrated, and they will now be described, by way of example only.

Referring to Figures 1 to 12, a total knee ieplacement prosthesis assembly 10 is shown for replacing a knee joint. The assembly shown in Figures 1 to 12 is suitable for replacing a left knee joint in a quadruped, however it will be undeistood that the features are also suitable for an assembly for implantation in a knee joint in a biped.

The assembly 10 comprises a femoral component 20 and a tibial component 30. The femoral component has a femoral stem 21 adapted to be received by an intremedullaiy canal of a femur.

The tibial component 30 comprises a tibial platform 32 and a bearing component 40 adapted to be arranged between the femoral component 20 and the tibial platform 32.

The bearing component 40 is a mobile bearing component.

Referring to Figure 9, the tibial platform 32 comprises a platform poition 33 and a tibial stem 34 adapted to be received by an intremedullaiy canal of a tibia. The platform portion 33 has a superior surface 33a that faces the bearing component 40 when assembled and an inferior surface 33b for facing the tibia when implanted. The superiol surface 33a has an abutment 35 extending away fiom it. The abutment 35 is a straight upstanding wall which projects away from the superior surface 33a, the abutment being disposed along the anterior edge of the platform portion 33, along a medial-lateial axis. The abutment 35 has a posterior face 35a that faces substantially posteriorly and a superior face 35b that faces superiorly when the tibial platform 32 is implanted. The posterior and superior faces 35a,35b are planar.

The platform portion 33 has a substantially cylindrical projection or post 36 extending away from the superior surface 33a of the platform portion. The post 36 extends substantially perpendicularly away from the superior surface 33a, the end of the post 36 furthest from the platform portion 33 being rounded.

Referring to Figure 8, the bearing component 40 is made of a suitable plastic material.

The bearing component has a superior surface 40a for facing the femoral component when assembled and an inferior surface 40b for facing the tibial platform 32 when assembled. The inferior surface 40b has an abutment recess 41 for receiving the abutment 35 when assembled. The abutment recess 41 has an inferior face 42, which is planar, for engaging with the superior face 35b of the abutment 35 when assembled.

The abutment recess 41 also has first and second faces 43a, 43b that face towards the posterior tace 35a of the abutment 35 when assembled. The first and second faces 43a, 43b are planar and slanted relative to one another. Each of the first and second faces 43a,43b extends from a respective side edge 44a,44b of the bearing component 40 to a common line 45 substantially at a mid-point between the medial and lateral sides 44a,44b of the bearing component 40. Referring to Figure 8, the bearing component has a projection recess or post recess 46 in its inferior surface 40b for receiving the post 36 of the tibial platform 32. The post recess 46 is shaped to receive the post 36, the post recess being substantially cylindrical in shape and having a concavely curved end. The diameter of the post recess 46 is sized to provide a snug fit around the post 36. This provides for stable rotation of the bearing component 40 relative to the tibial platform 32. Alternatively the diameter of the post recess 46 may be larger than that of the post 36, to allow for some translation of the bearing component 40 relative to the tibial platform 32 when assembled.

Referring to Figure 10, when assembled, the bearing component sits on the tibial platform 32 with the post 36 extending into the post recess 46. The inferior surface 40b of the bearing component 40 rests on the superior surface 33a of the platform portion 33. The inferior face 42 of the abutment recess 41 in the bearing component 40 sits over and engages the superior face 35b of the abutment 35. When assembled the bearing component 40 is rotatable relative to the tibial platform 32 in a plane parallel with the superior surface 33a of the platform portion 33 to a degree allowed for by the constraints of the first and second faces 43a,43b of the abutment recess 41, which engage with the abutment 35 at the limits of external and internal rotation of the knee joint.

Referring to Figure 4, the superior surface 40a of the bearing component 40 will now be described. The bearing component 40 has an intercondylar projection 50 extending away from it. The intercondylar projection 50 has a surface 51 that is convexly curved in the sagittal plane, but which is not curved in the coronal plane. The intercondylar projection 50 has side surfaces 52 which are substantially flat and parallel with one another. As can be seen from Figure 4, the superior surface 40a of the bearing component 40 is concavely curved, providing a pair of condyle depressions 53 arranged on either side of the intercondylar projection 50. Each of the condyle depressions 53 is concavely curved in the sagittal plane, but not curved in the coronal plane.

The superior surface 40a of the bearing component 40 has a stop element 54 extending therefrom. The stop element 54 is a straight upstanding wall which projects away from the superior surface 40a, the stop element 54 being disposed along the anterior edge of the bearing component 40. along a medial-lateral axis. The stop element 54 is convexly curved in the sagittal plane.

Referring to Figure 5A, the femoral component has a condylar portion 22 and a patellar portion 23. The condylar portion has a pair of laterally spaced apart parallel condyles 24. Each of the condyles 24 is convexly curved in the sagittal plane. As can be seen from Figure 5A, the condyles 24 are not curved in the coronal plane.

Referring to Figure 5A, the femoral component 20 has an intercondylar recess 26, arranged between the femoral condyles 24 for receiving the intercondylar projection 50 when assembled. The intercondylar recess 26 is shaped to receive the intercondylar projection 50, the intercondylar recess 26 having side surfaces which are substantially flat and parallel with one another, the surface between being concavely curved in the sagittal plane (but not curved in the coronal plane).

The femoral condyles 24 have a substantially constant radius of curvature. The condyle depressions 53 in the bearing component 40 also have a substantially constant radius of curvature, which substantially matches that of the femoral condyles 24.

The patellar portion 23 of the femoral component has spaced apart lateral portions that are convexly curved and a mid portion that merges smoothly with the lateral portions and is concavely curved, the concavely curved mid portion forming a patellar track 25 for slidingly receiving a prosthetic or natural patella when implanted. The patellar track for use in a femoral component for a quadruped will be deeper than that of prior art knee joint assemblies for humans, to provide better stability for the joint in a quadruped. Furthermore, as seen in Figure 4, the patellar track 25 is elevated compared to that of prior art knee joint assemblies for humans. The elevated and captive patellar track 25 matches the natural bone geometry of a quadruped, such as a canine.

Referring to Figure 7, the femoral component 20 has a stop element recess 27 disposed between the condylar portion 22 and a patellar portion 23 of the femoral component. The stop element recess 27 is formed of first and second portions, one on either side of the opening to the patellar track 25. The first and second portions of the stop element recess are each convexly curved in the sagittal plane, and shaped to conform with the convex curvature of the stop element 54.

Referring to Figures 1 and 7, when assembled, the femoral component 20 sits over the bearing component 40 with the intercondylar projection 50 received within the intercondylar recess 26 and the femoral condyles 24 seated in the condyle depressions 53. The congruent curved surfaces of the femoral condyles 24 seated in the condyle depressions 53 provide unbroken contact between the femoral component 20 and bearing component 40 during extension and flexion of the joint prosthesis assembly.

Referring to Figure 1, during extension of the joint, the stop element 54 engages in the stop element recess 27 at the predetermined limit of extension to be accommodated by the joint prosthesis, to prevent hyperextension of the joint.

Referring to Figure 2 the tibial stem 34 extends from a point on the inferior surface of the platform portion 33 that is offset medially from a notional mid-point between the medial and lateral sides of the tibial platform. This allows the tibial stem 34 to be optimally located relative to the femoral stem 21 for implantation of the tibial stem 34 in the tibia of a quadruped such as a canine or feline, which unlike the longitudinal axes of the femur and tibia of a human which tend to be substantially lined up with one another, tend to have a tibia that is medially offset from the femur. Different tibial platforms 32 will be provided for replacement of the left and right knee joint to allow for the tibial stem offset. Figures 1 to 12 show an assembly for replacement of a left knee joint.

The tibial platform for replacement of a right knee joint will be a mirror image of the tibial platform 32 for a left knee joint, in the sagittal mirror plane.

Referring to Figure 11, the inferior surface 33b of the platform portion 33 is stippled to promote attachment to the proximal tibial bone surface. The tibial platform 32 has a web portion 37 extending between the tibial stem 34 and the platform portion 33 to strengthen the tibial platform 32.

The femoral and tibial stems may be cemented or uncemented stems.

The parts of assembly of the present invention can be provided in different sizes to suit different joint sizes.

The knee joint prosthesis of the present invention includes an anatomical femoral component with a deep groove for patellar tracking and a central pocket between the condyles for the plastic bearing component to provide central stabilising support during flexion/extension and a stem or an extension shaft for attachment to the remaining segment of the femoral bone, a tibial component with a post to match with the hole in the plastic bearing component to provide stable attachment for the plastic whilst allowing it to rotate about the post through small angular motion restrained by a rail on the top face of the tibial component and a stem to fit straight into the marrow cavity of the tibial bone, a plastic bearing component to fit between the tibial and the femoral components with articulating surface on both top and bottom faces thus forming a total hinged knee joint replacement.

Claims

Claims 1. A total knee replacement prosthesis assembly comprising a femoral component and a tibial component, the tibial component comprising a tibial platform and a bearing component adapted to be arranged between the femoral component and tibial platform when assembled, the bearing component being rotatable relative to the tibial platform when assembled, wherein the tibial platform has a superior surface that faces the bearing component when assembled and an inferior surface for facing a tibia when implanted, the superior surface of the tibial platform having an abutment extending away from it, to limit the amount by which the bearing component can rotate relative to the bearing component in use.
2. A total knee replacement prosthesis assembly according to claim 1, wherein the abutment has a posterior face for facing substantially posteriorly when implanted, the posterior face being planar.
3. A total knee replacement prosthesis assembly according to any preceding claim, wherein the bearing component has a superior surface and an inferior surface, the inferior surface of the bearing component having an abutment recess for receiving the abutment when assembled.
4. A total knee replacement prosthesis assembly according to claim 3, wherein the abutment recess has first and second faces for facing towards the posterior face of the abutment when assembled, the first and second faces slanting relative to one another.
5. A total knee replacement prosthesis assembly according to claim 4, wherein each of the first and second faces extends from a respective first and second side edge of the bearing component to a line substantially at a mid-point between the medial and lateral sides of the bearing component, the first and second faces each slanting in an anterior direction from the respective side edge to said line substantially at the mid-point between the medial and lateral sides of the bearing component.
6. A total knee replacement prosthesis assembly comprising a femoral component and a tibial component, wherein the tibial component has a projecting stop element, the femoral component having a corresponding stop element recess for engaging with the stop element to prevent hyperextension of the joint.
7. A total knee replacement prosthesis assembly according to claim 6, wherein the femoral component has a condylar portion and a patellar portion, each having an external surface, the stop element recess being between the condylar portion and a patellar portion.
8. A total knee replacement prosthesis assembly according to claim 6 or 7, wherein the stop element recess is an elongate groove, extending substantially along a medial-lateral axis of the femoral component.
9. A total knee replacement prosthesis assembly according to any of claims 6 to 8, wherein the stop element is an elongate protrusion extending substantially along a medial-lateral axis of the femoral component.
10. A total knee replacement prosthesis assembly according to any preceding claim, wherein the condylar portion comprises a pair of laterally spaced apart condyles.
11. A total knee replacement prosthesis assembly according to any preceding claim, wherein the patellar portion comprises a patellar track which is shaped to conform with a natural or prosthetic patella.
12. A total knee replacement prosthesis assembly comprising a femoral component and a tibial component, wherein the femoral component has a pair of condyles and the tibial component has a corresponding pair of condyle depressions for receiving the respective condyles of the femoral component, each of the condyles being convexly curved in the sagittal plane and each of the condyle depressions being concavely curved in the sagittal plane, the radius of curvature of each condyle substantially matching the radius of curvature of the corresponding condyle depression.
13. A total knee replacement prosthesis assembly according to claim 12, wherein the condyle depressions are curved in the sagittal plane only.
14. A total knee replacement prosthesis assembly according to claim 12 or 13, wherein the condyles are curved in the sagittal plane only.
15. A total knee replacement prosthesis assembly according to any of claims 10 to 14, wherein the condyles and condyle depressions each have a substantially constant radius of curvature in the sagittal plane.
16. A total knee replacement prosthesis assembly comprising a femoral component and a tibial component, the tibial component having a tibial platform adapted for implantation on a subject's tibial plateau, the tibial platform having a tibial stem adapted to be received by an intremedullary canal of a tibia bone, wherein the tibial stem extends from a point on the tibial platform that is offset medially from a notional mid point between the medial and lateral sides of the tibial platform.
17. A total knee replacement prosthesis assembly according to any preceding claim, wherein the tibial component comprises a tibial platform and a bearing component adapted to be arranged between the femoral component and the tibial platform when assembled.
18. A total knee replacement prosthesis assembly according to claim 17, wherein the assembly further comprises a projection and a corresponding projection recess for receiving the projection when assembled, the projection extending away from the tibial platform or the bearing component and the recess being disposed in the other of the tibial platform or bearing component.
19. A total knee replacement prosthesis assembly according to claim 18, wherein the projection extends away from the tibial platform and is received in a corresponding projection recess in the bearing component when assembled.
20. A total knee replacement prosthesis assembly according to any preceding claim, wherein the assembly further comprises an intercondylar projection extending from a superior surface of the tibial component, the femoral component having a corresponding intercondylar recess for receiving the intercondylar projection.
21. A total knee replacement prosthesis assembly according to claim 20, wherein the tibial component comprises a tibial platform and a bearing component adapted to be arranged between the femoral component and the tibial platform when assembled and the intercondylar projection extends from a superior surface of the bearing component.
22. A total knee replacement prosthesis assembly according to claim 21 or 22, wherein the intercondylar projection is convexly curved in the sagittal plane.
23. A total knee replacement prosthesis assembly according to claim 22, wherein the intercondylar projection is curved in the sagittal plane only.
24. A total knee replacement prosthesis assembly according to any of claims 20 to 23, wherein the intercondylar projection has side surfaces which are substantially flat and parallel.
25. A total knee replacement prosthesis assembly according to any preceding claim, the femoral component having a femoral stem adapted to be received by an intremedullary canal of a femur bone,
26. A total knee replacement prosthesis assembly according to any preceding claim, the tibial component comprising a tibial platform and a bearing component adapted to be arranged between the femoral component and tibial platform when assembled, wherein the tibial platform has a superior surface that faces the bearing component when assembled and an inferior surface for facing a tibia when implanted, the superior surface of the tibial platform having an abutment extending away from it, to limit the amount by which the bearing component can rotate relative to the bearing component in use.
27. A total knee replacement prosthesis assembly according to claim 26, wherein the abutment has a posterior face for facing substantially posteriorly when implanted, the posterior face being planar.
28. A total knee replacement prosthesis assembly according to claim 26 or 27, wherein the bearing component has a superior surface and an inferior surface, the inferior surface of the bearing component having an abutment recess for receiving the abutment.
29. A total knee replacement prosthesis assembly according to claim 28, wherein the abutment recess has first and second faces for facing towards the posterior face of the abutment when assembled, the first and second faces slanting relative to one another.
30. A total knee replacement prosthesis assembly according to claim 29, wherein each of the first and second faces extends from a respective first and second side edge of the bearing component to a line substantially at a mid-point between the medial and lateral sides of the bearing component, the first and second faces each slanting in an anterior direction from the respective side edge to said line substantially at the mid-point between the medial and lateral sides of the bearing component.
31. A total knee replacement prosthesis assembly according to any preceding claim, wherein the tibial component has a projecting stop element, the femoral component having a corresponding stop element recess for engaging with the stop element to prevent hyperextension of the joint.
32. A total knee replacement prosthesis assembly according to claim 31, wherein the femoral component has a condylar portion and a patellar portion, each having an external surface, the stop element recess being between the condylar portion and a patellar portion.
33. A total knee replacement prosthesis assembly according to claim 31 or 32, wherein the stop element recess is an elongate groove, extending substantially along a medial-lateral axis of the femoral component.
34. A total knee replacement prosthesis assembly according to any of claims 31 to 33, wherein the stop element is an elongate protrusion extending substantially along a medial-lateral axis of the femoral component.
35. A total knee replacement prosthesis assembly according to any of claims 31 to 34, wherein the condylar portion comprises a pair of laterally spaced apart condyles.
36. A total knee replacement prosthesis assembly according to any of claims 31 to 35, wherein the patellar portion comprises a patellar track which is shaped to conform with a natural or prosthetic patella.
37. A total knee replacement prosthesis assembly according to any preceding claim, wherein the femoral component has a pair of condyles and the tibial component has a corresponding pair of condyle depressions for receiving the respective condyles of the femoral component, each of the condyles being convexly curved in the sagittal plane and each of the condyle depressions being concavely curved in the sagittal plane, the radius of curvature of each condyle substantially matching the radius of curvature of the corresponding condyle depression.
38. A total knee replacement prosthesis assembly according to claim 37, wherein the condyle depressions are curved in the sagittal plane only.
39. A total knee replacement prosthesis assembly according to claim 37 or 38, wherein the condyles are curved in the sagittal plane only.
40. A total knee replacement prosthesis assembly according to any of claims 37 to 39, wherein the condyles and condyle depressions each have a substantially constant radius of curvature in the sagittal plane.
41. A total knee replacement prosthesis assembly according to any preceding claim, wherein the tibial component has a tibial platform adapted for implantation on a subject's tibial plateau, the tibial platform having a tibial stem adapted to be received by an intremedullary canal of a tibia bone, wherein the tibial stem extends from a point on the tibial platform that is offset medially from a notional mid point between the medial and lateral sides of the tibial platform.
42. A total knee replacement prosthesis assembly substantially as hereinbefore described with reference to any suitable combination of the accompanying drawings.