GB2429648A

GB2429648A - Partial knee prosthesis

Info

Publication number: GB2429648A
Application number: GB0517678A
Authority: GB
Inventors: Gursharan Singh Chana
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-08-31
Filing date: 2005-08-31
Publication date: 2007-03-07
Also published as: GB0517678D0

Abstract

The invention provides either a medial or lateral knee implant for use in a knee joint. The medial knee implant comprises (a) a tibial tray; (b) a tibial insert; and (c) a femoral component; wherein the knee implant does not comprise any lateral component for location on the lateral tibial condyle or the lateral femoral condyle. The invention also provides a lateral knee implant for use in a knee joint comprising: (a) a tibial tray; (b) a tibial insert; and (c) a femoral component; wherein the knee implant does not comprise any medial component for location on the medial tibial condyle or the medial femoral condyle. The tibial tray may be made from cobalt-chromium and/or cobalt-chromium-molybdenum and/or titanium. The superior face of the tibial tray may be cobalt-chromium whilst the osseus face of the tray may be titanium.

Description

KNEE PROSTHESES

The present invention relates to an improved knee prosthesis, and to improved knee replacement methods.

Procedures for total knee replacement involve the removal of a thin layer of bone from the surface of both the tibia and the femur and the insertion of a prosthesis comprising a tibia! component and a femoral component to replace the removed bearing surface. However, in order to improve access to the joint area during surgery, in particular to provide sufficient clearance for insertion of the tibial component and the femoral component, current procedures require cruciate ligament sacrifice.

However, in many cases the sacrificed cruciate ligament or ligaments are healthy. Therefore it would be desirable to be able to maintain the cruciate ligaments in the knee in the event that they are still sufficiently healthy when the knee replacement is carried out.

Further, it has been determined that the majority of patients with osteoarthritis of the knee have the arthritis in only the medial tibio femoral compartment and the patella femoral compartment, with the lateral tibio femora! compartment being spared from, or significantly less affected by, the arthritis. Whilst uni-compartmental knee replacement is ::::. known in the art, in which only the medial tibio femoral compartment is *. 25 replaced, this technique does not assist if both the medial tibio femoral * * compartment and the patella femoral compartment require replacement, and until now patients in this situation would require total knee replacement surgery.

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Accordingly, it would be desirable to be able to replace both the medial tibio femoral component and the patella femoral compartment, whilst being able to maintain the lateral tibio femoral compartment if it is sufficiently free from arthritis.

Equally, it may be the case that a patient with osteoarthritis of the knee had the arthritis in only the lateral tibio femoral compartment and the patella femoral component, with the medial tibio femoral compartment being spared from, or significantly less affected by, the arthritis.

Accordingly, it would also be desirable to be able to replace the lateral tibio femoral compartment and the patella femoral compartment, whilst being able to maintain the medial tibio femoral compartment if it is sufficiently free from arthritis.

Accordingly, there is a need for a knee joint prosthesis and related method of knee replacement whereby both of the cruciate ligaments may be retained and one out of the lateral tibio femoral compartment and the medial tibio femoral compartment may also be retained.

In accordance with a first aspect of the present invention, there is provided a medial knee implant for use in a knee joint comprising: (a) a tibia! tray suitable for implantation in the knee joint, which tibia! tray comprises a medial portion, for location on the medial tibia! plateau of a prepared tibia, that has a superior face suitable for bearing a tibia! insert, and an osseus face, opposite the superficial face, suitable for : .. attachment to said tibia; S...

. 25 (b) a tibial insert suitable for implantation in the knee joint, which *S..

* tibia! insert comprises a medial portion, for location over the medial tibial tray of a tibia, that has an articular face that is shaped to engage and * articulate with a femoral component on the medial femoral condyle, and an inferior face, opposite the articular face, shaped to fit with the superior face of the tibia! tray; and (c) a femoral component suitable for implantation in the knee joint, which femoral component comprises (i) a medial condylar portion, for location on the medial femoral condyle of a femur, that has an articular face that is shaped to engage and articulate with the tibial insert, and an osseus face, opposite the articular face, suitable for attachment to the medial femoral condyle of said femur, and (ii) an anterior portion, for location on the anterior surface of the femur, that has an articular face that is shaped to engage and articulate with the patella, and an osseus face, opposite the articular face, suitable for engagement with said femoral anterior surface; wherein the knee implant does not comprise any lateral component for location on the lateral tibia! condyle or the lateral femora! condyle.

It should be noted that although the implant does not comprise any lateral component for location on the lateral tibia! condyle or the lateral femoral condyle, the anterior portion (ii) of the femoral component, which is for location on the anterior surface of the femur, has an articular face that is shaped to engage and articulate with the patella and for this to be achieved this anterior portion will have both a medial part for location over the medial side of the anterior surface of the femur and a lateral part for location over the lateral side of the anterior surface of the femur.

In accordance with an alternative first aspect of the present invention, there is provided a lateral knee implant for use in a knee joint *...

. 25 comprising: * S..

* (a) a tibial tray suitable for implantation in the knee joint, which tibial tray comprises a lateral portion, for location on the lateral tibia! 0*s plateau of a prepared tibia, that has a superior face suitable for bearing a tibial insert, and an osseus face, opposite the superior face, suitable for attachment to said tibia; (b) a tibial insert suitable for implantation in the knee joint, which tibial insert comprises a lateral portion, for location over the lateral tibial condyle of a tibia, that has an articular face that is shaped to engage and articulate with a femoral component on the lateral femoral condyle, and an inferior face, opposite the articular face, shaped to fit with the superior face of the tibial tray; and (c) a femora! component suitable for implantation in the knee joint, which femoral component comprises (i) a lateral condylar portion, for location on the lateral femoral condyle of a femur, that has an articular face that is shaped to engage and articulate with the tibial insert, and an osseus face, opposite the articular face, suitable for attachment to the lateral femoral condyle of said femur, and (ii) an anterior portion, for location on the anterior surface of the femur, that has an articular face that is shaped to engage and articulate with the patella, and an osseus face, opposite the articular face suitable for engagement with said femoral anterior surface; wherein the knee implant does not comprise any medial component for location on the medial tibia! condyle or the medial femoral condyle.

It should be noted that although the implant does not comprise any medial component for location on the medial tibial condyle or the medial femoral condyle, the anterior portion (ii) of the femoral component, which is for location on the anterior surface of the femur, has an articular face that is ::::. shaped to engage and articulate with the patella and for this to be achieved this anterior portion will have both a medial part for location S...

over the medial side of the anterior surface of the femur and a lateral part * for location over the lateral side of the anterior surface of the femur. I..

S

For each of the knee implants of the first aspect, the following applies. SS *S * S S * .

The implant may be a trial implant or a definitive implant. When the implant is a trial implant it comprises a trial tibial tray, a trial tibial insert, and a trial femoral component. When the implant is a definitive implant it comprises a definitive tibial tray, a definitive tibial insert, and a definitive femoral component.

The tibial tray may be any suitable material or combination of materials for use in a prosthesis. For example, the tray may be metal or metal alloy, such as cobalt-chromium or cobalt-chromium-molybdenum or titanium, or may be plastic such as polyethylene. Preferably, the tray is at least partially titanium. For example, the tray may be partially titanium and partially cobalt-chromium, or may be entirely titanium. In one embodiment, the superior face of the tray is cobalt-chromium, whilst the osseus face of the tray is titanium, such as beaded titanium.

If the tibial tray is a trial tibial tray, it is suitably provided with one or more holes, with each hole extending from the superior face to the osseus face. Accordingly, when the tray is located on the tibia a drill can be passed thorough the or each hole to drill a corresponding hole in the surface of the tibia below, which holes can be used in securing the definitive tray to the tibia.

If the tibia! tray is a definitive tibial tray, it is suitably provided with one ::::. or more tugs, with the or each lug extending from the osseus face away *. 25 from the tray. Accordingly, when the tray is located on the tibia the tugs * can be used to secure the tray onto the surface of the tibia below by a:. location of the tugs in prepared holes on the tibia! surface. S.

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In one embodiment, the tibia! tray is provided with a single lug. This lug may suitably be a fin-type lug; suitably it may be a lug substantially in the shape of a semi-circle or half oval.

The tibial insert may be any suitable material or combination of materials for use in a prosthesis. For example, the insert may be metal or metal alloy, such as cobalt-chromium or cobalt-chromium-molybdenum or titanium, or may be a plastic, such as polyethylene, in particular high- density polyethylene. In one embodiment the insert is ultra high molecular weight polyethylene.

The tibial insert suitably has a curved articular face to allow for engagement and articulation with a femoral component. Preferably, the articular face is curved both from front to back and from side to side.

The curvature of the articular face is preferably concave.

The femoral component may be any suitable material or combination of materials for use in a prosthesis. For example, the component may be metal or metal alloy, such as cobalt-chromium or cobalt-chromium- molybdenum or titanium. In one embodiment the femoral component is partially cobalt-chromium and partially titanium; for example it may be cobalt-chromium, such as cobbled cobalt-chromium, on its articular face and titanium on its osseus face.

The articular face of the condylar portion (i) of the femoral component is preferably curved so as to allow for engagement and articulation with the tibial insert. In particular, the articular face of this condylar portion (i) *. 25 of the femoral component may be curved both from front to back and from side to side. The curvature is suitably convex. *S.

It is advantageous for the articular face of the condylar portion (i) of the femoral component to be curved from both front to back and side to side, as this means that articulation of the femoral component with a tibia! insert is possible in both the autro posterior and the lateral planes of the knee. This clearly allows for improved movement of the prosthetic knee.

The condylar portion (i) may suitably include a posterior portion, which is shaped and sized to extend up the posterior surface of the femur, on the same side (medial or lateral) as the condylar portion (i).

The articular face of the anterior portion (ii) of the femoral component is preferably curved so as to allow for engagement and articulation with the patella. In particular, this articular face of the anterior portion (ii) of the femoral component may be curved both from top to bottom and from side to side. The curvature is suitably concave.

The anterior portion (ii) is shaped and sized to extend across both the medial anterior femoral surface and the lateral anterior femoral surface.

The anterior portion (ii) may suitably be substantially tongue shaped.

The anterior portion (ii) may include a cut away portion, for example a V shaped cut away portion, towards its base, on the side (medial or lateral) that the condylar portion (i) does not cover.

Preferably, the femoral component has a substantially U-shaped cross section, with the condylar portion (i) forming the base of the U, the condylar portion (i) having a posterior portion, which is shaped and sized :.:::. to extend up the posterior surface of the femur, that forms one arm of the U, and the anterior portion (ii) forming the other arm of the U. * I* If the femoral component is a trial femoral component, it is suitably * provided with one or more holes, with each hole extending from the articular face to the osseus face. Accordingly, when the femoral component is located on the femur a drill can be passed thorough the or each hole to drill a corresponding hole in the surface of the femur below, which holes can be used in securing the definitive femoral component to the femur.

If the femoral component is a definitive femoral component, it is suitably provided with one or more lugs, with the or each lug extending from the osseus face away from the femoral component. Accordingly, when the femoral component is located on the femur the lugs can be used to secure the femoral component onto the surface of the femur below by location of the lugs in prepared holes on the femoral surface.

In one embodiment, the femoral component is provided with two or more lugs extending from the osseus face.

Preferably, the femoral component is provided with one lug that extends from the osseus face of the anterior portion (ii), at the base of the anterior portion, the lug being located substantially centrally when considering the maximum width of the femoral component from the medial side to the lateral side. Accordingly, this lug can be used to attach the femoral component to the femur at a point near to the inter condylar notch of the femur.

Preferably, the femoral component is also provided with one lug that extends from the osseus face of the condylar portion (i), being located ::::. near to the base of the anterior portion (ii). Accordingly, this lug can be . 25 used to attach the femoral component to the femur at a point on the S...

* * : :* medial/i ateral femoral condyle. S..

Suitably, the knee implant may further comprise: (d) a pateila component suitable for implantation in the knee joint, which patella component has an articuiar face that is shaped to engage and articulate with the anterior portion (ii) of the femoral component, and an osseus face, opposite the articular face, suitable for attachment to said patella.

The patella component may be a trial patella component or a definitive patella component, depending upon whether the knee implant is trial or definitive.

The patella component may be any suitable material or combination of materials for use in a prosthesis. For example, the patella component may preferably be a plastic, such as polyethylene, in particular high- density polyethylene. Alternatively, the patella component may be metal or metal alloy, such as cobalt-chromium or cobalt-chromium-molybdenum or titanium. In one embodiment, the patella component is ultra high molecular weight polyethylene.

If the patella component is a trial component, it is suitably provided with one or more holes, with each hole extending from the articular face to the osseus face. Accordingly, when the component is located on the patella a drill can be passed thorough the or each hole to drill a corresponding hole in the surface of the patella below, which holes can be used in securing the definitive patella component to the patella.

If the patella component is a definitive component, it is suitably provided ::::. with one or more lugs, with the or each lug extending from the osseus face away from the patella component. Accordingly, when the patella component is located on the patella the lugs can be used to secure the patella component onto the surface of the patella below by location of the S. lugs in prepared holes on the patella surface.

S

S S

The patella component may suitably be sized and shaped in accordance with known designs for patella inserts.

The invention further provides, in a second aspect, a method of knee replacement, which method comprises: a) preparing the medial tibia! surface to receive an implant; b) preparing the medial femoral surface to receive an implant; and c) inserting a medial knee implant as defined above.

The invention further provides, in an alternative of the second aspect, a method of knee replacement, which method comprises: a) preparing the lateral tibial surface to receive an implant; b) preparing the lateral femoral surface to receive an implant; and c) inserting a lateral knee implant as defined above.

Such methods are advantageous, as they do not require the sacrifice of the anterior or posterior cruciate ligament.

Suitably, the method further comprises the step of: preparing the articular pate!la surface to receive an implant; wherein the knee implant that is inserted in step (c) is an implant comprising a patella component as defined above.

Suitably, the knee implant that is inserted in step (c) may be a trial implant as defined above, and the method further comprises: :.:::. testing the trial implant; and inserting a definitive knee implant as defined above. * S.

A specific embodiment of the present invention will now be described, by S..

S means of example only, with reference to the drawings, in which: S.....

S

Figure la is a view from above of a definitive tibia! tray that is part of a knee insert in accordance with the invention; Figure lb is a cross section through line A-A of the tibial tray shown in Figure la; Figure lc is a cross section through line B-B of the tibia! tray shown in Figure la; Figure 2a is a view from above of a definitive tibia! insert that is part of a knee insert in accordance with the invention; Figure 2b is a cross section through line C-C of the tibia! insert shown in Figure 2a; Figure 2c is a cross section through line D-D of the tibia! insert shown in Figure 2a; Figure 3a is a front view of a definitive femoral component that is part of a knee insert in accordance with the invention; Figure 3b is a cross section through line E-E of the femoral component shown in Figure 3a; Figure 3c is a cross section through line F-F of the femoral :.:::. component shown in Figure 3a; and S...

S I S...

Figure 3d is a cross section through line G-G of the femoral component shown in Figure 3a.

Figures la-c show a definitive tibia! tray 1 that is part of a definitive :. 30 medial knee insert in accordance with the present invention. The tray 1 comprises a medial portion 2, which is substantially semi circular in shape and is shaped and sized for location on the medial tibial condyle of a prepared tibia. The medial portion 2 has a superior face 2a suitable for bearing a tibia! insert, and an osseus face 2b, opposite the superior face, suitable for attachment to said tibia.

The osseus face 2b is provided with lug 3 to allow attachment of the tray 1 to the medial tibia! condyle of the prepared tibia. The lug 3 is located substantially centrally on the osseus face 2b, and is substantially semiovular in shape.

The superior face 2a of the tray 1 is cobalt-chromium, whilst the osseus face 2b and lug 3 of the tray are beaded titanium.

Figures 2a-c show a definitive tibial insert 4 that is part of a definitive medial knee insert in accordance with the present invention. The insert 4 consists of a medial portion, which is substantially semi circular in shape and is shaped and sized for location over the medial tibial condyle of a tibia, by being placed on the tibia! tray 1.

The insert 4 has an articular face 4a that is shaped to engage and articulate with a femoral component on the medial femoral condyle. This face is concave and is curved both from front to back and from side to side, as can be seen from Figures 2b and c. The insert 4 also has an inferior face 4b, opposite the articular face 4a, shaped to fit with the superior face 2a of the tibial tray 1. * *1

The insert 4 is ultra high molecular weight polyethylene.

Figures 3a-c show a definitive femoral component 5 that is part of a definitive medial knee insert in accordance with the present invention.

The femoral component 5 comprises a medial portion 6 which is substantially rectangular and is shaped and sized for location on the medial femoral condyle of a femur. The medial portion 6 has an articular face 6a that is shaped to engage and articulate with the tibia! insert 4.

This face 6a of the femoral component 5 is convex, being curved both from front to back and from side to side. The medial portion 6 also has an osseus face 6b, opposite the articular face 6a, suitable for attachment to the medial femoral condyle of said femur.

The femoral component 5 further comprises an anterior portion 7 which is substantially tongue shaped and is shaped and sized for location on the anterior surface of the femur. This anterior portion extends from the medial side to the lateral side, as compared to the medial portion 6 which is only on the medial side.

The anterior portion 7 has an articular face 7a that is shaped to engage and articulate with the patella. This articular face 7a is concave, being curved both from top to bottom and from side to side, so as to allow for engagement and articulation with the patella.

The anterior portion 7 also has an osseus face 7b, opposite the articular face 7a, shaped to fit against the anterior face of said femur.

The femoral component 5 is provided with two lugs 8a, 8b to allow : *. attachment of the femoral component 5 to the medial femoral condyle of the prepared femur.

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The lug 8a extends from the osseus face 6b of the medial portion 6, being *. 0 located near to the base of the anterior portion 7. Accordingly, this lug can be used to attach the femoral component 5 to the femur at a point on the medial femoral condyle.

The lug 8b extends from the osseus face 7b of the anterior portion 7, at the base of the anterior portion 7, the lug being located substantially centrally when considering the maximum width of the femoral component from the medial side to the lateral side. Accordingly, this lug can be used to attach the femoral component to the femur at a point near to the inter condylar notch.

The femoral component is cobalt-chromium on its articular faces 6a and 7a and titanium on its osseus faces 6b and 7b.

The skilled man will understand that a corresponding definitive lateral knee implant, trial medial knee implant and/or trial lateral knee implant could also be obtained by making appropriate modifications to the described definitive medial knee implant.

Procedure The following procedure is described in relation to a medial knee implant.

However, the skilled man will understand that this procedure could be appropriately modified for use in relation to a lateral knee implant.

Medial Tibial Cut An extra-medullary tibial jig is secured and the stylus is used to find the : lowest point of the medial tibia! plateau. This is the reference point for the deepest coronal cut. A coronal cut is made sufficiently far in the lateral direction that it is just medial to the tibia! spines. SI.

The depth of cut is 2-3mm below the!owest defect of media! tibial plateau. S. S* * S * .

A seggital cut is made just medial to the tibial spines, sparing the anterior cruciate ligament and posterior cruciate ligament.

The cut portion of the tibia is used to size up the tibial tray.

Femoral cut An intra-medullary hole is made above and medial to the femoral notch.

An intra-medullary rod provided with an anterior femoral condylar cutting device is inserted into the hole. The anterior femoral condyle is excised with three degrees of external rotation, just preventing anterior femoral cortical notching.

A distal femoral cutting and champher device is then attached to the rod.

A distal femoral cut, on the medial side only, is made at 8cm with the usual valgus of three to nine degrees. A usual valgus of five degrees is commonly used.

If necessary, a secondary distal cut can be made at 11cm.

Anterior champher cuts are made both medially and laterally. A posterior condylar cut is made only on the medial side. A posterior champher cut is also made only on the medial side, leaving the normal lateral femoral condyle intact. S... a * S...

A trochlear jig is applied and the trochlear cut made. The flexion gap and extension gap are measured to check that they are the same. If, however, the flexion gap is smaller than the extension gap then this can be rectified by taking more of the posterior femoral condyle on the medial Patella preparation The patella is cut using a patella jig, keeping at least 10mm of the patella thickness.

Insertion A tibial trial tray is inserted onto the prepared proximal tibial surface and lugholes are made in the surface through the holes in the tray. These lugholes are for the fixation of the definitive tibial tray onto the proximal tibia! surface using its lugs. The appropriate sized trial tibial insert is secured on the tibial tray.

A trial femoral component is inserted onto the femoral surface with the knee in hyper flexion. The knee is then straightened and joints tested for ligament stability, in relation to both the collaterals and the cruciates. A ligament balance test is then carried out. A patella trial component is inserted. The joint is then tested for patella tracking.

If all the trial implants are satisfactory, definitive implants are cemented in place, starting with the tibia! tray implant 2 then the femoral component 5 and then the tibial insert 4. The patella component (not shown) is cemented last. * SI * S S * S.. * S** * S *SSS * SS * S S * SS 5. *

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S S SS 55 * S I

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Claims

1. A medial knee implant for use in a knee joint comprising: (a) a tibia! tray suitable for implantation in the knee joint, which tibial tray comprises a medial portion, for location on the medial tibia! plateau of a prepared tibia, that has a superior face suitable for bearing a tibial insert, and an osseus face, opposite the superficial face, suitable for attachment to said tibia; (b) a tibial insert suitable for implantation in the knee joint, which tibia! insert comprises a medial portion, for location over the medial tibia! tray of a tibia, that has an articular face that is shaped to engage and articulate with a femoral component on the medial femoral condyle, and an inferior face, opposite the articular face, shaped to fit with the superior face of the tibial tray; and (c) a femoral component suitable for implantation in the knee joint, which femoral component comprises (i) a medial condylar portion, for location on the medial femoral condyle of a femur, that has an articular face that is shaped to engage and articulate with the tibial insert, and an osseus face, opposite the articular face, suitable for attachment to the medial femoral condyle of said femur, and (ii) an anterior portion, for location on the anterior surface of the femur, that has an articular face that is shaped to engage and articulate with the patella, and an osseus face, opposite the articular face, suitable for engagement with said femoral anterior surface; wherein the knee implant does not comprise any lateral component for location on the lateral tibia! condyle or the lateral femoral condyle.

2. A lateral knee implant for use in a knee joint comprising: (a) a tibial tray suitable for implantation in the knee joint, which tibial tray comprises a lateral portion, for location on the lateral tibia! plateau of a prepared tibia, that has a superior face suitable for bearing a tibia! insert, and an osseus face, opposite the superior face, suitable for attachment to said tibia; (b) a tibial insert suitable for implantation in the knee joint, which tibia! insert comprises a lateral portion, for location over the lateral tibial condyle of a tibia, that has an articular face that is shaped to engage and articulate with a femoral component on the lateral femoral condyle, and an inferior face, opposite the articular face, shaped to fit with the superior face of the tibia! tray; and (c) a femoral component suitable for implantation in the knee joint, which femoral component comprises (i) a lateral condylar portion, for location on the lateral femoral condyle of a femur, that has an articular face that is shaped to engage and articulate with the tibial insert, and an osseus face, opposite the articular face, suitable for attachment to the lateral femoral condyle of said femur, and (ii) an anterior portion, for location on the anterior surface of the femur, that has an articular face that is shaped to engage and articulate with the patella, and an osseus face, opposite the articular face suitable for engagement with said femoral anterior surface; wherein the knee implant does not comprise any medial component for location on the medial tibia! condyle or the medial femoral condyle.

3. An implant according to Claim 1 or Claim 2, wherein the tibia! tray is cobalt-chromium and/or cobalt-chromium-molybdenum and/or titanium.

4. An implant according to Claim 3, wherein the superior face of the tray is cobalt-chromium, whilst the osseus face of the tray is titanium.

5. An implant according to any one of the preceding claims wherein the tibial tray is provided with a single lug.

6. An implant according to any one of the preceding claims wherein the tibial insert is ultra high molecular weight polyethylene.

7. An implant according to any one of the preceding claims wherein the tibial insert has a curved articular face to allow for engagement and articulation with a femoral component.

8. An implant according to Claim 7 wherein the articular face of the tibial inert is curved both from front to back and from side to side.

9. An implant according to Claim 7 or Claim 8 wherein the curvature of the articular face of the tibia! insert is concave.

10. An implant according to any one of the preceding claims wherein the femoral component is partially cobalt-chromium and partially titanium.

11. An implant according to Claim 10 wherein the femoral component is cobalt-chromium on its articular face and titanium on its osseus face.

12. An implant according to any one of the preceding claims wherein the articular face of the condylar portion (i) of the femoral component is curved so as to allow for engagement and articulation with the tibial insert.

13. An implant according to Claim 12 wherein the articular face of the condylar portion (i) of the femoral component is curved both frotn front to back and from side to side.

14. An implant according to Claim 12 or Claim 13 wherein the curvature of the articular face of the condylar portion is convex.

15. An implant according to any one of the preceding claims wherein the condylar portion (i) of the femoral component includes a posterior portion, which is shaped and sized to extend up the posterior surface of the femur, on the same side as the condylar portion (i).

16. An implant according to any one of the preceding claims wherein the articular face of the anterior portion (ii) of the femoral component is curved so as to allow for engagement and articulation with the patella.

17. An implant according to Claim 16 wherein the articular face of the anterior portion (ii) of the femoral component is curved both from top to bottom and from side to side.

18. An implant according to Claim 16 or Claim 17 wherein the curvature of the articular face of the anterior portion (ii) is concave.

19. An implant according to any one of the preceding claims wherein the anterior portion (ii) is substantially tongue shaped.

20. An implant according to any one of the preceding claims wherein the anterior portion (ii) includes a cut away portion, towards its base, on the side that the condylar portion (i) does not cover.

21. An implant according to any one of the preceding claims wherein the femoral component has a substantially U-shaped cross section, with the condylar portion (i) forming the base of the U, the condylar portion (i) having a posterior portion, which is shaped and sized to extend up the posterior surface of the femur, that forms one arm of the U, and the anterior portion (ii) forming the other arm of the U.

22. An implant according to any one of the preceding claims wherein the femoral component is provided with two or more lugs extending from the osseus face.

23. An implant according to any one of the preceding claims wherein the implant further comprises: (d) a patella component suitable for implantation in the knee joint, which patella component has an articular face that is shaped to engage and articulate with the anterior portion (ii) of the femoral component, and an osseus face, opposite the articular face, suitable for attachment to said patella.

24. An implant according to Claim 23 wherein the patella component is ultra high molecular weight polyethylene.

25. A medial or lateral knee implant for use in a knee joint substantially as hereinbefore described and with reference to the drawings.