GB2312167A

GB2312167A - An endoprosthetic knee

Info

Publication number: GB2312167A
Application number: GB9607923A
Authority: GB
Inventors: Michael Anthony Tuke
Original assignee: FINSBURY
Current assignee: FINSBURY
Priority date: 1996-04-17
Filing date: 1996-04-17
Publication date: 1997-10-22
Also published as: GB9607923D0

Abstract

Comprising at least one unicompartmental, or one bicompartmental, tibial plate 1 having a smooth proximal face and a distal face, anchoring means on said distal face for anchoring the plate to the proximal end of a resected tibia, and at least one guide means 5 upstanding from the proximal face of the tibial plate; and at least one unicompartmental meniscal component 6 having a substantially flat distal face for glidable seating on the tibial plate and a dished proximal face for receiving an articulating surface of a femoral component, the meniscal component having formed in its distal face a cavity 9 which is adapted to receive loosely the guide means of the tibial plate and to permit limited gliding movement of the meniscal component upon the tibial plate. The tibial component may include an upstanding abutment (11) at its medial edge.

Description

MENISCAL KNEE PROSTHESIS The present invention relates to meniscal knee prostheses.

Conventionally, two principal types of endoprosthetic knee are known. The first type, the so-called total knee, comprises a tibial plate and a femoral component with an intervening meniscal component, each component having medial and lateral sides. Typically the tibial plate and femoral compartment are made from a suitable metal or metal alloy, such as an alloy of cobalt and chromium, whereas the meniscal components are made from a synthetic plastics material, for example ultra high molecular weight polyethylene. In most designs the meniscal component is fixed to the tibial plate. In other designs it is free to float to a certain extent with respect to the tibial plate in order that the prosthesis shall mimic better the natural movement of the knee. The total knee is designed to replace all of the articulating surfaces of the knee.

The second type of endoprosthetic knee, the so-called unicompartmental knee, also has a tibial plate, a femoral component and an intervening meniscal component. However, in this case, only a medial or, alternatively, a lateral femorotibial replacement is provided. Again it is usual for the meniscal component to be fixed to the tibia but in some designs there is provided a certain floating movement of the meniscal component.

A third type of endoprosthetic knee, referred to herein as the "biunicompartmental" type comprises two unicompartmental knee prostheses used, one on each of the lateral and medial sides, to replace all of the articulating surfaces of the femoro-tibial articulation.

In a variation on the total knee prosthesis, it is possible to have a single tibial plate with medial and lateral portions upon which are seated two separate meniscal components, one meniscal component upon each of the respective medial and lateral portions of the tibial plate.

When using a total knee replacement, it is possible for a surgeon to retain the patient's posterior cruciate ligament which can be accommodated within a cut-out portion in the centre of the posterior part of the tibial plate. However, it is not usually practical, when using this type of knee replacement, to preserve the anterior cruciate ligament, should this be intact. In order to accommodate the anterior cruciate ligament, the cut-out portion in the tibial plate has to be of such magnitude that the integral strength of the tibial plate is weakened beyond that which is acceptable.

The unicompartmental knee prosthesis generally requires that both posterior and anterior cruciate ligaments are retained by the surgeon, the knee being otherwise essentially normal.

There is a desire amongst surgeons working in this field to preserve the patient's anterior cruciate ligament if possible. Accordingly, in some indications, surgeons have made use of two unicompartmental prostheses to replace the total knee prosthesis. However, unicompartmental and "bi-unicompartmental" knee prostheses have suffered from certain disadvantages which have rendered them unpopular except in very specific indications.

One of the problems experienced by the unicompartmental and "biunicompartmental" meniscal knee prostheses is that the meniscal component has a tendency to slip out of the articulation between femur and tibia in some circumstances, causing locking of the knee and extreme pain to the patient.

One conventional knee addresses this problem to a certain extent by providing a non-round meniscal component with a high anterior lip and controlled rotationally by a raised lip running the length of the edge of the tibial component adjacent the tibial eminence, against which the meniscal component abuts. The meniscal component is thereby afforded a degree of freedom of movement such as is necessary to mimic the range of motion of the human knee but is also constrained so as not to rotate across the sagittal plane of the knee.

However, this type of prosthesis is still not immune from dislocation and has remained somewhat unpopular for this reason. Despite its prolonged availability, its use as a "bi-unicompartmental" knee has remained very rare, surgeons preferring to use this type of prosthesis as a unicompartmental knee only.

It is therefore an object of the present invention to provide an improved meniscal unicompartmental, "bi-unicompartmental", or total knee for use in knee arthroplasty.

According to the present invention there is provided an endoprosthetic knee comprising: a tibial plate having a smooth proximal face and a distal face, anchoring means on the distal face for anchoring the plate to the proximal end of a resected tibia, and at least one guide means upstanding from the proximal face of the tibial plate; and at least one unicompartmental meniscal component having a substantially flat distal face for glidable seating on the tibial plate and a dished proximal face for receiving an articulating condylar surface of a femoral component anchorable to the distal end of a resected femur, the meniscal component having formed in its distal face a cavity which is adapted to receive loosely the or a guide means of the tibial plate and to permit limited gliding movement of the meniscal component upon the tibial plate.

Preferably, the femoral component is arranged to be fully congruent with the meniscal component.

Preferably the proximal face of the tibial plate is polished so as to facilitate movement of the meniscal component thereon.

The endoprosthetic knee of the invention is a compartmentalised endoprosthetic knee. It may be a unicompartmental knee. This allows only one side of the femoro-tibial joint to be replaced. An advantage of such a unicompartmental knee is that the surgeon is not required to sacrifice the patient's anterior cruciate ligament, should this ligament be sufficiently intact. A further advantage of a unicompartmental knee in accordance with the invention is that it allows, in use, a degree of subluxation of the joint owing to the rotational and/or rectilinear slippage of the meniscal component upon the tibial plate. However, whilst a degree of subluxation is permitted, luxation or excessive subluxation is prevented by the tibial plate guide means limiting the range of movement of the meniscal component. The facility of a degree of subluxation with minimal danger of luxation or excessive subluxation is a particularly advantageous feature of endoprosthetic knees in accordance with the invention. In this regard, the endoprosthetic knee mimics the full range of motion of the human knee, in which a degree of subluxation is possible because of the resilience of the semilunar fibro-cartilages on the head of the tibia.

Yet another advantageous feature of such a unicompartmental endoprosthetic knee is that the endoprosthesis is less invasive than in conventional total knee arthroplasty for most indications, in which total knee endoprostheses are generally used.

It is preferred that in a unicompartmental endoprosthetic knee according to the present invention the gliding movement of the meniscal component upon the tibial plate includes a degree of rotation of the meniscal component, about the axis of the tibia upon the tibial plate, of up to about 20 " in total.

An advantageous feature of an endoprosthetic knee in accordance with the invention is that the patient can expect, after knee arthroplasty, to have an improved range of movement in the joint in comparison with conventional unicompartmental knees, but with a significant reduction in the corresponding danger of dislocation and associated pain and in the risk of need for further surgery.

Preferably, in a unicompartmental endoprosthetic knee in accordance with the of the invention, the gliding movement of the meniscal component upon the tibial plate includes a degree of rectilinear slippage in an anterior-posterior direction, preferably of not more than about 8mm. It is further preferred that the gliding movement of the meniscal component upon the tibial plate includes a degree of rectilinear slippage in a medial-lateral direction, preferably of not more than about 4mm. Advantageously for the user, truly congruent surfaces of the femur and meniscal component can be maintained whilst still allowing a range of articulation in the prosthesis due to the gliding movement of the meniscal component upon the tibial plate.

The endoprosthetic knee of the invention may alternatively be designed as a "bi-unicompartmental" knee prosthesis. Thus the invention further provides an endoprosthetic knee comprising: a first tibial plate having a smooth proximal face and a distal face, anchoring means on the distal face for anchoring the plate to the lateral side of the proximal end of a resected tibia, and first guide means upstanding from the proximal face of the first tibial plate; a second tibial plate having a smooth proximal face and a distal face, anchoring means on the distal face for anchoring the plate to the medial side of the proximal end of the resected tibia, and second guide means upstanding from the proximal face of the second tibial plate; a first unicompartmental meniscal component having a substantially flat distal face for glidable seating on the first tibial plate and a dished proximal face for receiving an articulating surface of a first condyle of a femoral component anchorable to a distal end of a resected femur, the first meniscal component having formed in its distal face a first cavity adapted to receive loosely the first guide means of the first tibial plate and to permit limited gliding movement of the first meniscal component upon the first tibial plate; and a second unicompartmental meniscal component having a substantially flat distal face for glidable seating on the second tibial plate and a dished proximal face for receiving an articulating surface of a second condyle ofthe femoral component, the second meniscal component having formed in its distal face a second cavity adapted to receive loosely the second guide means of the second tibial plate and to permit limited gliding movement ofthe second meniscal component upon the second tibial plate.

The endoprosthetic knee of the invention may alternatively be designed as a total knee prosthesis. Thus the invention further provides an endoprosthetic knee comprising: a tibial plate having a smooth proximal face, a distal face, a medial component and a lateral component, anchoring means on the distal face for anchoring the plate to the proximal end of a resected tibia, first guide means upstanding from the proximal face of the medial component of the tibial plate, and second guide means upstanding from the proximal face of the lateral component of the tibial plate; a first unicompartmental meniscal component having a substantially flat distal face for glidable seating on the medial component of the tibial plate and a dished proximal face for receiving an articulating surface of a first condyle of a femoral component anchorable to a distal end of a resected femur, the first meniscal component having formed in its distal face a first cavity adapted to receive loosely the first guide means of the tibial plate and to permit limited gliding movement of the first meniscal component upon the medial component of the tibial plate; and a second unicompartmental meniscal component having a substantially flat distal face for glidable seating on the lateral component of the tibial plate and a dished proximal face for receiving an articulating surface of a second condyle of the femoral component, the second meniscal component having formed in its distal face a second cavity adapted to receive loosely the second guide means of the tibial plate and to permit limited gliding movement of the second meniscal component upon the lateral component of the tibial plate.

Many indications currently requiring total knee arthroplasty of the traditional type may be treated more expeditiously and easily using such a total or "biunicompartmental" knee endoprosthesis. Thus, total knee arthroplasty may be effected less invasively and more effectively than has previously been the case and, in the case of the "bi-unicompartmental" knee prosthesis according to the invention, without the need to sacrifice the anterior cruciate ligament, should this be sufficiently intact.

Because of the freedom of movement provided to the user by the prosthesis of the invention, it is possible for the meniscal component thereof to be arranged to receive a corresponding femoral component with true congruency. Congruency between the femoral and meniscal components reduces the amount of wear of the meniscal component and increases its working life compared to conventional prostheses in which true congruency is not maintained.

A total or "bi-unicompartmental" endoprosthetic knee according to the invention may be provided with a single femoral component having lateral and medial condylar portions for articulation with the respective first and second meniscal component dished proximal faces. Alternatively, there may be provided two separate lateral and medial femoral components for articulation with respective meniscal component dished proximal faces.

The or each guide means may comprise an elongate raised portion having a substantially anterior-posterior longitudinal axis. In one such arrangement, the meniscal component cavity may comprise an elongate slot having a substantially anterior-posterior longitudinal axis, the relative dimensions of the elongate portion of the guide means and of the elongate slot being such as to permit limited movement of the guide means within the cavity. Such movement may include rectilinear slippage as well as rotational movement about the axis of the tibia.

Alternatively, the or each guide means may comprise a plurality of tibial plate guide members. For example, two or more cylindrical pegs upstanding from the proximal face of the tibial plate may be arranged in loose fit registry with the meniscal component cavity. It is also envisaged that the or each meniscal component may be provided with a plurality of meniscal component cavities. Thus, for example, two cylindrical guide members may be arranged in loose fit registry with two cylindrical cavities.

The or each meniscal component is dished on its proximal face to receive an articulating surface of a condyle of the femur, or femoral component, and has a marginal portion that is relatively thicker than the dished portion. The meniscal component cavity is preferably situated in the thicker marginal portion of the meniscal component.

One advantage of such an arrangement is that the depth of the meniscal component cavity, and hence the height of the tibial plate guide means, can be maximised, thereby minimising the risk of dislocation of the meniscal component from the tibial plate, an event which would have severe and painful consequences for the patient. Another advantage is that the aforementioned risk of dislocation can be minimised whilst the danger ofthe cavity becoming exposed on the proximal face of the meniscal component, due to wear of the meniscal component, is also minimised. Another advantage ofthe pair of menisci in a total knee according to the invention is that correct centering of congruent articulation of the menisci is automatically established. This is particularly advantageous in that it minimises wear and damage to the plastic meniscus. It is also an advantage that materials other than plastic may be used. For example, all components of the prosthesis may be manufactured from cobalt chrome alloy (i.e. femur, tibia and mensici in a uni, total or biunicompartmental knee).

The tibial plate may be provided at its median or midline edge with an upstanding abutment member against which the edge of the meniscal component abuts at the limit of its rotational and/or rectilinear movement. This feature has the additional advantage of providing a further safeguard against excessive movement of the meniscal component upon the tibial plate beyond the limits of the preferred range of movement described above.

In order that the invention may be clearly understood and readily carried into effect, a number of specific embodiments thereof will now be described with particular reference to the accompanying drawings in which: Figure 1 (a) shows a top plan view, partially in outline, of two mirrorimage tibial plates and corresponding meniscal components of a first embodiment ofthe invention; Figure l(b) shows a cross-section on a line A-A of Figure 1(a); Figure l(c) shows a cross-section on line B-B of Figure 1(a); Figure 2(a) shows a top plan view, partially in outline, of two mirrorimage tibial plates and corresponding meniscal components of a second embodiment of the invention; Figure 2(b) is a cross-section on line C-C of Figure 2(a); Figure 2(c) is a cross-section on line D-D of Figure 2(a); Figure 3(a) shows a top plan view, partially in outline, oftwo mirrorimage tibial plates and meniscal components of a third embodiment of the invention.

Figure 3(b) shows a cross-section on line E-E of Figure 3(a); Figure 3(c) shows a cross-section on line F-F of Figure 3(a); Figure 4(a) shows a top plan view, partially in outline, of a tibial plate and corresponding mirror-image meniscal components of a fourth embodiment of the invention; Figure 4(b) shows a cross-section on line G-G of Figure 4(a); Figure 5(a) shows a top plan view, partially in outline, of a tibial plate and corresponding meniscal component of a fifth embodiment of the invention; and Figure 5(b) is a cross-section on line H-H of Figure 5(a).

Referring to Figure 1 there is shown a tibial plate 1 having a smooth proximal face 2 and a distal face 3. Tibial plate 1 comprises a longitudinal pin 4 extending from the distal face 3 of tibial plate 1, pin 4 being adapted for insertion into a longitudinal cavity drilled in the patient's tibia to anchor the tibial plate to the bone.

Optionally, ancillary anchoring means may also be used. These may comprise one or more further pegs which may be ribbed for extra adhesiveness. In addition, distal face 3 may be dimpled to provide better adhesion to the bone surface. Such methods and means for anchoring the tibial plate to the bone are known and are well understood by those skilled in the art.

On proximal face 2 of tibial plate 1 there is provided an upstanding guide member 5 which, in the embodiment of Figure 1, is a raised wall on proximal face 2. Preferably, guide member 5 is of unitary construction with tibial plate 1. Tibial plate 1 is preferably made from an alloy of cobalt and chromium. The dimensions of tibial plate 1 may vary for different patients and/or for different indications.

Particularly, the thickness of tibial plate 1 is normally from about 2mm to about 4mm.

Meniscal component 6 is seated on tibial plate 1 and is shown only in outline in Figure l(a). Meniscal component 6 has a substantially flat distal face 7 for glidable seating on proximal face 2 of tibial plate 1. Meniscal component 6 also has a dished proximal face 8 for receiving a femoral component (not shown). Meniscal component 6 may be constructed from ultra high molecular weight polyethylene.

Alternatively, a metal component 6, for example of cobalt chromium alloy, may be used. The dimensions of the meniscal component may vary for different patients and/or indications. In particular, the thickness of the meniscal component is normally between about 5mm and 15mm at the thinnest central portion of the meniscal component.

Endoprosthetic knees according to the invention may be manufactured to fit various bone sizes. The combined thickness of the tibial plate and meniscal component together with the femoral component for use therewith may be chosen to match a particular flexion/extension gap which the surgeon has cut. Normally, femoral components which are commercially available are manufactured with a standard thickness of about 9mm. The combined thickness of the tibial plate and meniscal component is preferably between about 7mm and about 1 7mm, for example 7mm, 9.5mm, 12mm, 14.5mm or 17mm.

On its distal face 7 meniscal component 6 is provided with cavity 9 which is shaped to receive guide member 5 of tibial plate 1 in a loose fit arrangement such that gliding movement of meniscal component 6 upon tibial plate 1 is limited by the extent of freedom of movement of guide member 5 within cavity 9.

As is best seen from Figure 1(c), guide member 5 is preferably located in a marginal portion of tibial plate 1 such that corresponding cavity 9 in meniscal component 6 can be formed in the thickest available portion of meniscal component 6, taking into account the dishing in proximal face 8. This is a particularly advantageous arrangement when meniscal component 6 is made from a material such as ultra high molecular weight polyethene which is subject to wear. If meniscal component 6 were to wear away sufficiently to expose guide member 5 through proximal face 8, this could have disastrous consequences for the patient. This is a particularly relevant consideration for younger and more active patients who are becoming the recipients of endoprosthetic knees more commonly than has been the case in the past.

Figure 2 depicts an alternative embodiment of the invention wherein two guide members 5 are provided. Instead of a continuous wall, the guide member therefore comprises two upstanding pegs 5.

In Figure 3 a third embodiment of the invention is shown in which two cavities 9 are provided to accommodate two guide members 5.

In Figure 4 there is shown another embodiment of the invention which is designed for use as part of a total endoprosthetic knee. A tibial plate 1 having both medial and lateral compartments is provided with upstanding guide members 5 on which are located two meniscal components 6.

In Figure 5 there is shown an alternative embodiment of the invention, in which tibial plate 1 is provided at its medial edge 10 which an upstanding abutment member 11, against which medial edge 12 of meniscal component 6 abuts at the limit of its gliding movement upon tibial plate 1.

Claims

CLAIMS:

1. An endoprosthetic knee comprising: a tibial plate having a smooth proximal face and a distal face, anchoring means on the distal face for anchoring the plate to the proximal end of a resected tibia, and at least one guide means upstanding from the proximal face of the tibial plate; and a unicompartmental meniscal component having a substantially flat distal face for glidable seating on the tibial plate and a dished proximal face for receiving an articulating condylar surface of a femoral component anchorable to the distal end of a resected femur, the meniscal component having formed in its distal face a cavity which is adapted to receive loosely the or a guide means of the tibial plate and to permit limited gliding movement of the meniscal component upon the tibial plate.

2. An endoprosthetic knee according to claim 1, comprising: a first tibial plate having a smooth proximal face and a distal face, anchoring means on the distal face for anchoring the plate to the lateral side ofthe proximal end of a resected tibia, and first guide means upstanding from the proximal face of the first tibial plate; a second tibial plate having a smooth proximal face and a distal face, anchoring means on the distal face for anchoring the plate to the medial side of the proximal end of a resected tibia, and second guide means upstanding from the proximal face of the second tibial plate; a first unicompartmental meniscal component having a substantially flat distal face for glidable seating on the first tibial plate and a dished proximal face for receiving an articulating surface of a first condyle of a femoral component anchorable to a distal end of a resected femur, the first meniscal component having formed in its distal face a first cavity adapted to receive loosely the first guide means of the first tibial plate and to permit limited gliding movement of the first meniscal component upon the first tibial plate; and a second unicompartmental meniscal component having a substantially flat distal face for glidable seating on the second tibial plate and a dished proximal face for receiving an articulating surface of a second condyle of the femoral component, the second meniscal component having formed in its distal face a second cavity adapted to receive loosely the second guide means of the second tibial plate and to permit limited gliding movement ofthe second meniscal component upon the second tibial plate.

3. An endoprosthetic knee according to claim 1, comprising: a tibial plate having a smooth proximal face, a distal face, a medial component and a lateral component, anchoring means on the distal face for anchoring the plate to the proximal end of a resected tibia, first guide means upstanding from the proximal face of the medial component of the tibial plate, and second guide means upstanding from the proximal face of the lateral component of the tibial plate; a first unicompartmental meniscal component having a substantially flat distal face for glidable seating on the medial component of the tibial plate and a dished proximal face for receiving an articulating surface of a first condyle of a femoral component anchorable to a distal end of a resected femur, the first meniscal component having formed in its distal face a first cavity adapted to receive loosely the first guide means of the tibial plate and to permit limited gliding movement of the first meniscal component upon the medial component of the tibial plate; and a second unicompartmental meniscal component having a substantially flat distal face for glidable seating on the lateral component of the tibial plate and a dished proximal face for receiving an articulating surface of a second condyle of the femoral component, the second meniscal component having formed in its distal face a second cavity adapted to receive loosely the second guide means of the tibial plate and to permit limited gliding movement of the second meniscal component upon the lateral component of the tibial plate.

4. An endoprosthetic knee according to any one of claims 1 to 3, wherein the gliding movement of the or each meniscal component upon the or each tibial plate includes a degree of rotation of the component upon the plate of up to about 20 " in total.

5. An endoprosthetic knee according to any one of claims 1 to 4, wherein the gliding movement of the or each meniscal component upon the or each tibial plate includes a degree of rectilinear slippage in an anterior-posterior direction of up to about 8mm.

6. An endoprosthetic knee according to any one of claims 1 to 5, wherein the gliding movement of the or each meniscal component upon the or each tibial plate includes a degree of rectilinear slippage in a medial-lateral direction of up to about 4 mm.

7. An endoprosthetic knee according to any one of claims 1 to 6, wherein the or each guide means comprises an elongate portion having a substantially anteriorposterior longitudinal axis.

8. An endoprosthetic knee according to claim 7, wherein the or each meniscal component cavity comprises an elongate slot having a substantially anteriorposterior longitudinal axis, the relative dimensions of the elongate portion of the guide means and of the elongate slot being such as to permit limited movement of the guide means within the cavity.

9. An endoprosthetic knee according to any one of claims 1 to 7, wherein the or each meniscal component cavity is situated in a marginal portion of the meniscal component.

10. An endoprosthetic knee according to any one of claims 1 to 9, wherein a plurality of guide means are provided on the or each tibial plate.

11. An endoprosthetic knee according to claim 10, wherein a plurality of meniscal component cavities are provided in the or each meniscal component.

12. An endoprosthetic knee according to any one of claims 1 to 11, wherein the or each tibial plate is provided at its medial edge with an upstanding abutment member against which a medial edge of the or each meniscal component abuts at the limit of its rotational and/or rectilinear movement.

13. An endoprosthetic knee, in which the meniscal component is arranged to receive the femoral component as a truly congruent fit in articulation.

14. An endoprosthetic knee according to any one of claims 1 to 13, in which the or each meniscal component is made from a material selected from ultra high molecular weight polythene, cobalt chrome alloy, plastics material or a ceramic..

15. An endoprosthetic knee according to any one of claims 1 to 14, in which the femoral and/or tibial components are made from the sarne material as 15.

16. An endoprosthetic knee constructed and arranged as described herein, with particular reference to Figures 1 to 5.

16. An endoprosthetic knee according to claim 15, wherein the material is cobalt chrome alloy.

17. An endoprosthetic knee constructed and arranged as described herein, with particular reference to Figures 1 to 5.

Amendments to the claims have been filed as follows 1. An endoprosthetic knee comprising: a tibial plate having a smooth proximal face and a distal face, anchoring means on the distal face for anchoring the plate to the proximal end of a resected tibia, and at least one guide means upstanding from the proximal face of the tibial plate; and a unicompartmental meniscal component having a substantially flat distal face for glidable seating on the tibial plate and a dished proximal face for receiving an articulating condylar surface of a femoral component anchorable to the distal end of a resected femur, the meniscal component having formed in a marginal portion of its distal face a cavity which is adapted to receive loosely the or a guide means ofthe tibial plate and to permit limited gliding movement ofthe meniscal component upon the tibial plate.

2. An endoprosthetic knee according to claim 1, comprising: a first tibial plate having a smooth proximal face and a distal face, anchoring means on the distal face for anchoring the plate to the lateral side ofthe proximal end of a resected tibia, and first guide means upstanding from the proximal face of the first tibial plate; a second tibial plate having a smooth proximal face and a distal face, anchoring means on the distal face for anchoring the plate to the medial side of the proximal end of a resected tibia, and second guide means upstanding from the proximal face of the second tibial plate; a first unicompartmental meniscal component having a substantially flat distal face for glidable seating on the first tibial plate and a dished proximal face for receiving an articulating surface of a first condyle of a femoral component anchorable to a distal end of a resected femur, the first meniscal component having formed in a marginal portion of its distal face a first cavity adapted to receive loosely the first guide means of the first tibial plate and to permit limited gliding movement of the first meniscal component upon the first tibial plate; and a second unicompartmental meniscal component having a substantially flat distal face for glidable seating on the second tibial plate and a dished proximal face for receiving an articulating surface of a second condyle of the femoral component, the second meniscal component having formed in a marginal portion of its distal face a second cavity adapted to receive loosely the second guide means of the second tibial plate and to permit limited gliding movement of the second meniscal component upon the second tibial plate.

3. An endoprosthetic knee according to claim 1, comprising: a tibia1 plate having a smooth proximal face, a distal face, a medial component and a lateral component, anchoring means on the distal face for anchoring the plate to the proximal end of a resected tibia, first guide means upstanding from the proximal face of the medial component of the tibial plate, and second guide means upstanding from the proximal face of the lateral component of the tibial plate; a first unicompartmental meniscal component having a substantially flat distal face for glidable seating on the medial component of the tibial plate and a dished proximal face for receiving an articulating surface of a first condyle of a femoral component anchorable to a distal end of a resected femur, the first meniscal component having formed in a marginal portion of its distal face a first cavity adapted to receive loosely the first guide means of the tibial plate and to permit limited gliding movement of the first meniscal component upon the medial component of the tibial plate; and a second unicompartmental meniscal component having a substantially flat distal face for glidable seating on the lateral component of the tibial plate and a dished proximal face for receiving an articulating surface of a second condyle of the femoral component, the second meniscal component having formed in a marginal portion of its distal face a second cavity adapted to receive loosely the second guide means of the tibial plate and to permit limited gliding movement- of the second meniscal component upon the lateral component of the tibial plate.

4. An endoprosthetic knee according to any one of claims 1 to 3, wherein the gliding movement of the or each meniscal component upon the or each tibial plate includes a degree of rotation of the component upon the plate of up to about 20 in total.

9. An endoprosthetic knee according to any one of claims 1 to 8, wherein a plurality of guide means are provided on the or each tibial plate.

10. An endoprosthetic knee according to claim 9, wherein a plurality of meniscal component cavities are provided in the or each meniscal component.

11. An endoprosthetic knee according to any one of claims 1 to 10, wherein the or each tibial plate is provided at its medial edge with an upstanding abutment member against which a medial edge of the or each meniscal component abuts at the limit of its rotational and/or rectilinear movement.

12. An endoprosthetic knee according to any one of claims 1 to 11, in which the meniscal component is arranged to receive the femoral component as a truly congruent fit in articulation.

13. An endoprosthetic knee according to any one of claims 1 to 12, in which the or each meniscal component is made from a material selected from ultra high molecular weight polythene, cobalt chrome alloy, plastics material or a ceramic..

14. An endoprosthetic knee according to claim 13, in which the femoral and/or tibial components are made from the same material as the material of claim 13.

15. An endoprosthetic knee according to claim 14, wherein the material is cobalt chrome alloy.