GB2138296A - Knee prosthesis - Google Patents

Abstract

In an operation for correction of leg alignment in a patient with varus or valgus deformity, the surgeon selects one of a range of tibial knee components 1 which differ in the angle of inclination of their articular surfaces to their median planes and in the wedge angles of integral wedges 2 for occupying tibial condyle deficits. The surgeon also selects one of a range of metal spacing washers 13 of differing thicknesses and places it over and around an intramedullary stem 12 of a femoral component 6 to bring the articular surface of the component 6 to just the correct position along the femur. <IMAGE>

Description

SPECIFICATION Improvements in or relating to prosthetic knee-joint components According to one aspect of the present invention, there is provided a prosthetic tibial knee component having an articular surface which is inclined obliqueliy to the median plane of the component.

According to another aspect of the present invention, there is provided a knee joint replacement operation, comprising selecting a spacer from a range of spacers, and inserting said spacer between a prosthetic knee component and a bone to which said component is to be fixed, and fixing said component to said bone.

According to a further aspect of the present invention, there is provided knee joint replacement apparatus, comprising a prosthetic knee component, and a range of spacers from which a spacer can be selected for insertion between said component and a bone to which said component is to be fixed.

In order that the invention may be clearly understood and readily carried into effect, reference will now be made, by way of example, to the accompanying drawing, in which: Figure 1 shows a diagrammatic anterior elevation of a patient's knee joint following total knee replacement, Figure 2 shows an anterior perspective view of a tibial component of the prosthetic total knee, and Figure 3 shows an anterior elevation of a tibial knee component for use in revision surgery.

In patients with moderate or severe varus or valgus deformity, the greatest loss of bone is usually from one tibial condyle. The passive correction of leg alignment at operation would produce a triangular deficit between any new femoral articular surface and the worn tibial condyle. Therefore, in the tibial component 1 shown in Figures 1 and 2 of the drawings, a wedge 2 has been provided at the undersurface of the component 1 to make up the deficit. The underneath surface of the wedge 2 is at an angle X to the normal to the median plane M of the component 1.A range of components 1 can be produced with various angles X, for example X=0 , X=15", and X=30 , the 0 component being used for substantially no varus or valgus deformity, the 15 component being used for moderate such deformity, and the 300 component being used for severe such deformity. A locking hole 3 for cement is provided in the undersurface of the wedge 2 and a corresponding hole should be made in the sloping tibial plateau to help key the cement. The articular top surface of the component 1, which is in the form of a cylindrical depression to receive a corresponding surface of a femoral prosthetic component 6 is tilted at an angle Yto the normal to the median plane M.Longitudinal alignment of the component 1 relative to the tibia T is achieved by insertion of an intramedullary guide rod into a hole 4 which is formed in a stream 5 of the component 1 and the axis of which lies in the median plane M. The reason for the provision of a significant angle Y is that, with a long-standing moderate or severe varus or valgus deformity, a component with Y=0 but with X= 15 or 300, say, would usually give an under-correction of the tibio-femoral angle of about 20 or about 4 , since it would seem that the long-standing deformity would have caused bending of the bones of the limb, especially the tibia, and, even using a very long intramedullary guide rod, exact leg alignment in the coronal plane could not be restored.Therefore, the components with X=0O, 150 and 300 are given values of Y=0 , 20 and 4 , respectively.

Figure 3 shows a tibial component for use in revision surgery when there has been much loss of bone. The management of a patient in whom extensive surgery has failed is difficult. A caliper or wheelchair is usually unacceptable and amputation may be rejected. A revision arthroplasty using the tibial component 10 with its long stem 11 is possible if the posterior capsular ligament is intact. From a pre-operative radio-graph, it is possible to estimate the need for additional varus or valgus, which would be provided by the angle Y of the articular surface of the component 10 to the normal to the median plane M of the component 10. A range of components 10 is provided, with Y=OO, 30 and 6 , respectively, for example.

The posterior capsular ligament has three parts; two overlie the respective femoral condyles and a third, shorter part extends between them. These three parts normally limit extension at precisely the correct angle. After a total knee replacement operation, they can maintain lateral stability in full extension provided that the positions of the prosthetic articular surfaces along the tibia T and femur F are exactly correct. In the femoral component 6, a gap (not shown) between two metal condyles (not shown) at the back of the component 6 allows all three parts of the capsular ligament to become tight simultaneously in full extension and with correct tension.This provides immediate stability in extension and allows the collateral ligaments to heal during the early weeks after operation; eventually, these will provide lateral stability, not only in full extension, but through the 900 range of flexion. It is thus clear that stability in full extension is one of the fundamentals to the success of knee replacement. If fixed flexion is present after operation, muscle effort is wasted. If excessive hyperextension is allowed, the knee feels unstable and flexor and extensor muscles must act together to maintain a normal posture. The use of the posterior capsular ligament to define the exact position of the femoral component 6 ensures stability in full extension. After a component 1 has been fixed in place on the tibia T, whether with cement or otherwise, a component 6 is placed and used to ensure that sufficient bone has been removed from the end of the femur F to allow a few degrees of hyperextension. From a range of metal annular washers of various thicknesses, for example 1 mm., 2 mm. and 3 mm., the surgeon selects one which, when inserted over an intramedullar stem 12 of the component 6 to come to lie on the floor 13 of an upwardly facing concavity of the component 6, so as to act as a spacer between the component 6 and the femur F, brings the articular surface of the component 6 to just the correct position along the femur F. When the surgeon is satisfied that the spacing washer of the most appropriate thickness has been used, the component 6 is fixed to the femur F with the washer (referenced 14 in Figure 1) in position between them.

Claims (20)

1. A prosthetic tibial knee component having an articular surface which is inclined obliquely to the median plane of the component.

2. A component as claimed in claim 1, wherein said articular surface is inclined at an angle of no more than 60to said median plane.

3. A component as claimed in claim 1 or 2, and further comprising at its undersurface a wedge-form part for occupying a wear-produced space at a tibial condyle.

4. A component as claimed in claim 3, wherein said wedge-form part has a wedge angle of no more than 300.

5. A component as claimed in claim 3 or4, wherein said wedge has in its undersurface a locking hole for cement.

6. A component as claimed in any preceding claim, and further comprising a relatively short intramedullary stem.

7. A component as claimed in any preceding claim, and further comprising a hole which lies in said median plane and is arranged to receive an intramedullary guide rod for longitudinal alignment of the component relative to the tibia.

8. A component as claimed in claim 1 or 2, and further comprising a relatively long intramedullary stem.

9. A range of prosthetic tibial knee components having respective articular surfaces which differ from each other in their angles of inclination to the respective median planes of the components.

10. A range as claimed in claim 9, wherein all but one of said components further comprise at their undersurfaces respective wedge-form parts of differing wedge angles for occupying wear-produced spacers at tibial condyles.

11. A range as claimed in claim 10, wherein said components comprise first, second and third components having their respective said angles of inclination equal to approximately 0 , 20 and 4 , and the wedge angles of their respective wedge-form parts equal to approximately 0 , 150 and 30%

12. A range as claimed in claim 9, wherein said components comprise first, second and third components having their respective said angles of inclination equal to approximately 00, 30 and 60.

13. A joint replacement operation, comprising selecting a spacer from a range of spacers of differing thicknesses, and inserting said spacer between a prosthetic component and a bone to which said component is to be fixed, and fixing said component to said bone.

14. An operation as claimed in claim 13, wherein said inserting includes placing the spacer over and round an intramedullary stem of said component.

15. Joint replacement apparatus, comprising a prosthetic component, and a range of spacers of differing thicknesses from which a spacer can be selected for insertion between said component and a bone to which said component is to be fixed.

16. Apparatus as claimed in claim 15, wherein said range comprises spacers of respective thicknesses of approximately 1 millimetre, 2 millimetres and 3 millimetres.

17. A prosthetic tibial knee component, substantially as hereinbefore described with reference to Figure 2 or 3 of the accompanying drawing.

18. A range of prosthetictibial knee components, substantially as hereinbefore described with reference to Figure 2 or 3 of the accompanying drawing.

19. A knee joint replacement operation, substantially as hereinbefore described with reference to Figures 1 and 2, or Figure 3, of the accompanying drawing.

20. Knee joint replacement apparatus, substantially as hereinbefore described with reference to Figure 1 of the accompanying drawing.