GB2341803A

GB2341803A - A knee prosthesis

Info

Publication number: GB2341803A
Application number: GB9820692A
Authority: GB
Inventors: Stephen Jeremy Krikler; Peter Jeremy Gibson; Ian Hamilton Paling
Original assignee: Corin Medical Ltd
Current assignee: Corin Medical Ltd
Priority date: 1998-09-24
Filing date: 1998-09-24
Publication date: 2000-03-29
Anticipated expiration: 2018-09-24
Also published as: GB2341803B; GB9820692D0

Abstract

A knee prosthesis comprises a femoral component 11 and a tibial component 12. The femoral component and the tibial component have articulating surfaces of metal, ceramic material, glass, diamond or a diamond like material. Preferably, the tibial component comprises a fixed part 15 and a separate meniscal part 16 movable relative to the fixed part.

Description

2341803 -1A KNEE PROSTHESIS This invention relates to a knee prosthesis.

A conventional knee prosthesis comprises a metal femoral component and a polyethylene tibial component. The femoral component rotates whilst articulating with the tibial component and, therefore, the knee and tibial component are incongruent for a substantial part of the movement cycle. This problem has been overcome by providing a mobile meniscal component with a shaped upper side (superior surface) congruent with the femoral component, and a flat underside (inferior surface) to slide on the fixed tibial component. Such a three part knee is also more surgeon forgiving. In known 3-part knee prostheses, the meniscal component is made of ultra-high molecular weight polyethylene. However, polyethylene components abrade and it is now understood that polyethylene debris, caused as a result of abrasion through articulation, is a major cause of osteolysis and resultant failure of the knee prosthesis.

According to one aspect of the present invention there is provided a knee prosthesis comprising a femoral component and a tibial component, the femoral component and the tibia] component having articulating surfaces of metal, ceramic material, glass, diamond or a diamond like material.

The advantage of such a knee is that these materials abrade very much less than polyethylene components.

Preferred and/or optional features of the invention are set forth in Claims

2 to 17, inclusive.

According to another aspect of the invention there is provided a knee prosthesis comprising a femoral component and a patella, the femoral component and patella having articulating surfaces of metal, ceramic material, glass, diamond or a diamond like material.

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, wherein Figure 1 is a side sectional view of one embodiment of a knee prosthesis according to the invention, Figures 2 (a) to 2(c) are, respectively, underneath, front and side views of the meniscal part of the tibial component shown in Figure 1, Figures 3(a) to 3(c) are, respectively, plan, front and side views of the fixed part of the tibial component of the prosthesis of Figure 1, and Figure 4 is a sectional through the meniscal part of the tibial component, on a much enlarged scale.

Referring now to the drawings, the prosthesis 10 shown in Figure 1 is a total knee prosthesis and consists of a femoral component 11 and a tibial component 12. Ilie, femoral component 11 is of standard design and shape, having fixing devices such as a femoral stem 13, or alternatively pegs or screws, and condyles 14. This component can be made of any biocompatible metallic material suitable for the purpose, but is preferably formed of high carbon cobalt chromium alloy.

The tibial component 12 comprises a fixed part 15 and a separate meniscal part 16. Both parts 15 and 16 can be made of any biocompatible metallic material suitable for the purpose but are also preferably made of high carbon cobalt chromium alloy.

The meniscal part 16 has a generally planar inferior surface 17 and a superior surface 18 comprising two condylar surfaces, one on either side of the centre, each having a radius of curvature which is replicated in the articulating area of the meniscal part 16, such that the femoral component 11 and meniscal part 16, when in contact throughout the range of motion, are fully congruent. As shown in figure 4, the meniscal part is hollow to reduce its weight but has reinforcing struts 25 to ensure sufficient mechanical strength.

The inferior surface 17 of the meniscal part 16 also incorporates an anterior recess 19 and a posterior recess 20. The anterior recess 19 is substantially part circular in underneath view, having a part-cylindrical inner wall 19a and a relatively wide opening 19b in the side wall of the meniscal component 16. The posterior recess 20 is generally U-shaped in underneath view, having an arcuate end wall 20a -4 and substantially parallel side walls 20b. The distance between the parallel side walls 20b of the posterior recess 20 is less than the overall width of the anterior recess 19.

The fixed part 15 which supports the meniscal part 16 is illustrated in detail in Figures 3(a) to 3(c). The fixed part 15 has a planar superior surface or plateau 21, beneath which are located fixing devices such as pegs or stems 22. An anterior peg or bollard 23 and a posterior peg or bollard 24 are located on the plateau 21.

Each bollard 23, 24 is substantially cylindrical in shape and upstands from the plateau 21 by no more than the depth or the corresponding anterior and posterior recesses 19, 20 in the meniscal part 16. The anterior bollard 23 is smaller in diameter than the posterior bollard 24.

When the prosthesis is assembled, the fixed part 15 supports the meniscal part 16 which in turn supports the femoral component 11. The bollards 23, 24 engage in the recesses 19, 20 so that relative movement between the meniscal part 16 and the fixed part 15 is allowed but is restricted by the abutment of the bollards 23, 24 against the walls of the recesses 19, 20. The relative dimensions and spacings of the bollards 23, 24 and the recesses 19, 20 are typically such that a maximum anterior-posterior movement of substantially 5 min is allowed and a maximum medial lateral movement of substantially 4 inni is allowed. However, more or less is possible.

The fact that the anterior recess 19 is wider than the posterior recess 20, and also that the anterior bollard 23 is smaller in diameter than the posterior bollard 24, means that, when the posterior bollard 24 abuts against a side wall 20b of the posterior recess 20 at an extreme of medial-lateral movement, rotational movement of the meniscal part 16 with respect to the fixed part 15 about an axis passing through or close to the posterior bollard 24 is still possible. This is advantageous in helping to mimic very closely the action of a natural knee joint.

The upper surface of the fixed part 15 and the lower surface of the meniscal part 16 are highly polished so as to allow the meniscal part 16 to glide easily across the fixed part 15. The articulating surfaces of the femoral component 11 and the meniscal part 16 are also highly polished and are manufactured to a sphericity tolerance of less than 10 microns.

Bone-contacting surfaces of the femoral and tibial components 11 and 12 may have appropriately textured areas or porous coatings of materials such as Hydroxyapatite.

The patella is re-surfaced or replaced with an all-metal component, such that it articulates with the femoral component 11 in a fully congruent manner.

The prosthesis described above is a total prosthesis. However, it could be a partial prosthesis (i.e. a unicondylar prosthesis).

Also, although metal is presently preferred as the material for the femoral and tibial components, it is envisaged that they could be made of (or coated with) a -6ceramic material (e.g. alumina or zirconia) or glass or coated with diamond or a diamond like material. If coated with diamond, the meniscal part could be made of polyethylene and the fixed part of the tibial component and the femoral component could be coated metal.

The above embodiment is given by way of example only and various modifications will be apparent to persons skilled in the art without departing from the scope of the invention. For example, the bollards 23 and 24 and recesses 19 and 20 could be replaced by ramps and recesses as described, for example, in EP-A-0702537 or could be inclined or undercut to impede or prevent unintentional separation of the meniscal and fixed parts of the tibial component as described, for example, in GB2302282. Also, the fixed and meniscal parts of the tibial component could be integral with one another.

1 -7

Claims

1. A knee prosthesis comprising a femoral component and a tibial component, the femoral component and the tibial component having articulating surfaces of metal, ceramic material, glass, diamond or a diamond like material.

2. A knee prosthesis as claimed in Claim 1, wherein the femoral component has a radius of curvature which is replicated in the articulating area of the tibial component, such that both components, when in contact throughout the range of 10 motion, are fully congruent.

3. A knee prosthesis as claimed in Claim 1 or Claim 2, wherein the tibial component comprises a fixed part and a separate meniscal part movable relative to the fixed part.

4. A knee prosthesis as claimed in Claim 3, wherein the meniscal part is capable of anterior-posterior, medial-lateral and rotational movement relative to the fixed part.

5. A knee prosthesis as claimed in Claim 3 or Claim 4, wherein interengaging means are provided between the meniscal part and the fixed part of the tibial component so as to allow only limited anteriorposterior, medial-lateral and rotational movement between the meniscal part and the fixed part.

6. A knee prosthesis as claimed in Claim 5, wherein the interengaging means comprises one or more bollards on the superior surface of the fixed part of the tibial component and one or more recesses in the inferior surface of the metal meniscal part.

7. A knee prosthesis as claimed in any one of Claims 3 to 6, wherein the inferior surface of the meniscal part and the superior surface of the fixed part are highly polished.

8. A knee prosthesis as claimed in any one of the preceding claims, wherein the articulating surfaces of the femoral component and the tibial component are highly polished.

9. A knee prosthesis as claimed in any one of the preceding claims, wherein the articulating surfaces of the femoral component and the tibial component are manufactured to a sphericity tolerance of less than 10 microns.

10. A knee prostheses as in anyone of the preceding claims, wherein the femoral and tibial components are made in any biocompatible metallic material suitable for the purpose.

A knee prosthesis as claimed in Claim 10, wherein the femoral and tibial components are made of high carbon cobalt chromium alloy.

12. A knee prosthesis as claimed in any one of the preceding claims, wherein the patella is resurfaced with metal, ceramics material, glass, diamond or diamond like material or replaced with a component made of metal, ceramics material or glass such that it articulates with the femoral component in a fully congruent manner.

13. A knee prosthesis as claimed in claim 12, wherein the patella is manufactured from any biocompatible metallic material suitable for the purpose.

14. A knee prosthesis as claimed in Claim 13, wherein the patella component 10 is manufactured from high carbon cobalt chromium alloy.

15. A knee prosthesis as claimed in any one of Claims 3 to 7, or Claims 8 to 14 when dependent on Claim 3, wherein the meniscal component is hollow.

16. A knee prosthesis as claimed in Claim 15, wherein the hollow meniscal component has reinforcing struts to ensure sufficient mechanical strength.

17. A knee prosthesis as claimed in any one of the preceding claims, wherein at least some of the bone-contacting surfaces of the femoral and tibial components have a porous coating, e.g. a Hydroxyapatite coating, or are textured.

18. A knee prosthesis substantially as hereinbefore described with reference to the accompanying drawings.

-1019. A knee prosthesis comprising a femoral component and a patella, the femoral component and patella having articulating surfaces of metal, ceramic material, glass, diamond or diamond like material.