GB2302282A

GB2302282A - Knee prosthesis

Info

Publication number: GB2302282A
Application number: GB9512111A
Authority: GB
Inventors: George John James Cremore; Derek Redvers Cooper
Original assignee: Corin Medical Ltd
Current assignee: Corin Medical Ltd
Priority date: 1995-06-15
Filing date: 1995-06-15
Publication date: 1997-01-15
Anticipated expiration: 2015-06-15
Also published as: GB9512111D0; GB2302282B

Abstract

The prosthesis comprises a femoral component 12, a tibial component 30 and a meniscal component 20, the latter being capable of anterior-posterior, medial-lateral and rotational movement with respect to the tibial component, interengaging pegs 36, 38 and recesses 26, 28 being provided on the components 20, 30 which pegs and recesses have inclined or undercut walls such that unintentional separation of the meniscal and tibial components is impeded or prevented.

Description

KNEE PROSTHESIS The invention relates to a knee prosthesis, particularly, to a three-part knee prosthesis.

Strenuous efforts have been made to produce three-part knee prostheses which are capable of mimicking very closely the action of the natural knee joint. Inevitably, restraints acting between the tibial and meniscal components are normally required in order to provide the prosthesis with adequate stability.

However, the meniscal component must also be able to move fairly freely with respect to the tibial component so that the action of the natural knee joint can be mimicked. This can mean that, under certain circumstances, sufficient forces are present which force the meniscal and tibial components to become disengaged despite the presence of the restraints. Even when upstanding pegs are provided on the tibial component which engage with recesses in the meniscal component, separation can occur when the forces are sufficient to cause the lower surface of the meniscal component to ride up onto the upper surfaces of the upstanding pegs.

This can cause extreme discomfort to the recipient of the knee prosthesis.

An object of the invention is to provide a three-part knee prosthesis in which the unintentional separation of the meniscal and tibial components is impeded or prevented.

The invention provides a knee prosthesis as set out in claim 1. Advantageous features are set out in the subsidiary claims.

The presence of inclined or uncut walls on the pegs and recesses means that, to achieve separation of the tibial and meniscal components, a force acting to separate these components would be necessary. Such a force would be very unlikely to occur in a knee joint.

An embodiment of the present invention will now be described with reference to the accompanying drawings wherein: Figure 1 is a side sectional view of a knee prosthesis according to the invention; Figures 2a to 2c are, respectively, underneath, front and side views of the meniscal component of the prosthesis of Figure 1; and Figures 3a to 3c are, respectively, plan, front and side views of the tibial component of the prosthesis of Figure 1.

The prosthesis 10 shown in Figure 1 consists of a femoral component 12, a meniscal component 20 and a tibial component 30. The femoral component 12 is of standard design and shape, having fixing devices such a femoral stem 14, or alternatively pegs or screws, and condyles 16. The femoral component 12 actually forms no part of the present invention and will therefore be described no further here.

The meniscal component 20 is located between the femoral and tibial components 12,30 and is shown in detail in Figures 2a to 2c. The overall shape of the meniscal component 20 is of standard design, having a generally planar lower surface 22 and an upper surface 24 comprising condylar surfaces. The lower surface 22 of the meniscal component 20 also incorporates an anterior recess 26 and a posterior recess 28. The anterior recess 26 is substantially wedge shaped, both in plan view and in side view. The medial-lateral walls 26a and the posterior wall 26b are all inclined as shown in Figures 2b and 2c. The posterior recess 28 is of very similar shape with the medial-lateral walls 28a and the anterior wall 28b having a similar inclination as shown also in Figures 2b and 2c.

The tibial component 30 which supports the meniscal component 20 is illustrated in detail in Figures 3a to 3c. Again, the overall design of the tibial component 30 is standard in that it has a planar, highly polished upper surface or plateau 32 beneath which are located fixing devices such as pegs or stems 34. However, on the upper surface 32 are located an anterior peg or bollard 36 and a posterior peg or bollard 38. Each peg is substantially wedge-shaped in plan view and substantial trapezoidal in side view. The medial-lateral walls 26a,38a are inclined as shown in Figure 3b and the posterior wall 36b of the anterior peg and the anterior wall 38b of the posterior peg are also inclined as shown in Figure 3c.

When the prosthesis is assembled, the tibial component 30 supports the meniscal component 20 which in turn supports the femoral component 12. The pegs 36,38 engage in the recesses 26,28. The relative dimensions and spacing of the pegs 36,38 and recesses 26,28 is such that sufficient play is allowed to permit limited anterior-posterior, medial-lateral and rotational movement between the meniscal component 20 and the tibial component 30. The relative movement is restricted by the abutment of the pegs 36, 38 against the walls of the recesses 26,28. Furthermore, the inclination of the side walls 36a,36b,38a,38b of the pegs 36,38 and the side walls 26a,26b,28a,28b means that unintentional separation of the meniscal component 20 from the tibial component 30 is virtually impossible under the action of a force acting parallel to the surfaces 22,32.

It is advantageous if the femoral and tibial components 12,30 are manufactured from a chrome-cobalt alloy and the meniscal component 20 is manufactured from ultra-high molecular weight polyethylene. Texturing or coating of the pegs and/or stems 14,34 can be provided to encourage fixing with the recipient' s natural bone.

Claims

1. A knee prosthesis comprising a femoral component, a tibial component and a meniscal component located between the femoral and tibial components, the meniscal component being capable of anterior-posterior, medial-lateral and rotational movement with respect to the tibial component, wherein interengaging pegs and recesses are provided on the meniscal and tibial components, the pegs and recesses having inclined or undercut walls such that unintentional separation of the meniscal and tibial components is impeded or prevented.

2. A knee prosthesis as claimed in claim 1, wherein anterior and posterior pegs and recesses are provided, the pegs and recesses being located on an axis of symmetry of the respective component.

3. A knee prosthesis as claimed in claim 2, wherein each peg and recess has an inclined or undercut wall on each of its medial and lateral sides.

4. A knee prosthesis as claimed in claim 2 or 3, wherein each of the anterior peg and corresponding recess has an inclined or undercut wall on its posterior side and each of the posterior peg and corresponding recess has an inclined or undercut wall on its anterior side.

5. A knee prosthesis as claimed in any one of the preceding claims, wherein the superior surface of the tibial component and the inferior surface of the meniscal component are substantially planar.

6. A knee prosthesis as claimed in any one of the preceding claims, wherein the superior surface of the tibial component is highly polished.

7. A knee prosthesis as claimed in any one of the preceding claims, wherein the upstanding pegs and recesses are all substantially wedge-shaped in plan view.

8. A knee prosthesis substantially as herein described with reference to the accompanying drawings.

8. A knee prosthesis as claimed in any one of the preceding claims, wherein each peg is located on the tibial component and each recess is located in the meniscal component.

9. A knee prosthesis substantially as herein described with reference to the accompanying drawings.

Amendments to the claims have been filed as follows 1. A knee prosthesis comprising a femoral component, a tibial component and a meniscal component located between the femoral and tibial components, the meniscal component being capable of anterior-posterior, medial-lateral and rotational movement with respect to the tibial component, wherein anterior and posterior interengaging pegs and recesses are provided on the meniscal and tibial components, the pegs and recesses being located on an axis of symmetry of the respective component and having inclined or undercut walls such that unintentional separation of the meniscal and tibial components is impeded or prevented.

2. A knee prosthesis as claimed in claim 1, wherein each peg and recess has an inclined or undercut wall on each of its medial and lateral sides.

3. A knee prosthesis as claimed in claim 1 or 2, wherein each of the anterior peg and corresponding recess has an inclined or undercut wall on its posterior side and each of the posterior peg and corresponding recess has an inclined or undercut wall on its anterior side.

4. A knee prosthesis as claimed in any one of the preceding claims, wherein the superior surface of the tibial component and the inferior surface of the meniscal component are substantially planar.

5. A knee prosthesis as claimed in any one of the preceding claims, wherein the superior surface of the tibial component is highly polished.

6. A knee prosthesis as claimed in any one of the preceding claims, wherein the upstanding pegs and recesses are all substantially wedge-shaped in plan view.

7. A knee prosthesis as claimed in any one of the preceding claims, wherein each peg is located on the tibial component and each recess is located in the meniscal component.