GB1575278A

GB1575278A - Knee-joint endoprostheses

Info

Publication number: GB1575278A
Application number: GB2455178A
Authority: GB
Original assignee: Schuett & Grundei Sanitaet
Current assignee: Schuett & Grundei Sanitaet
Priority date: 1977-06-24
Filing date: 1978-05-30
Publication date: 1980-09-17
Also published as: FR2395014A2; CH630519A5; DE2728427C2; JPS6143471Y2; JPS5439997A; DE2728427A1; JPS61115519U; FR2395014B2

Abstract

For the patella embedded in the patellar ligament to be able to execute unimpeded its natural movement from the top outwards and in an arcuate manner downwards and inwards in a knee-joint endoprosthesis, there is provided, in an endoprosthesis composed of a tibial part and a femoral part in which the tibial part has two sliding surfaces separated by a web and the femoral part has two skids (13) held together by a bridge (14), that the stem (6) used for fastening the femoral part on the femur opposite the perpendicular, longitudinal mid-plane (17) of the joint cavity (16) be fastened on the bridge (14) in a manner offset relative to the outer skid (13c). This offset permits the patella to move from the top downwards and in an arcuate manner laterally inwards on the sliding surface formed by the front surface of the bridge and the front surface (13a) of the skids and resembling the anatomy of the natural joint. <IMAGE>

Description

(54) IMPROVEMENTS IN OR RELATING TO KNEE-JOINT ENDOPROSTHESES (71) We, SANITATSHAUS SCHUTT & GRUNDEI WERKSTATTEN FUR ORTHOPADIE-TECHNIK, an O.H.G., of 41, Wahmstrasse, D-2400 Lubeck, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to kneejoint endoprostheses and is an improvement in the invention claimed in co-pending application no. 46440/76 (Serial No.

1,534,187).

In accordance with the said co-pending application, when the knee-joint is in any bent position, the tibia section is allowed a limited rotary movement relative to the femur section as in a healty knee-joint and the femur section is able to perform a limited forwards movement in relation to the tibia section such as also occurs in a healthy knee-joint. The physiological pattern of movement by the parts of the prosthesis which can be achieved in this way prevents strain on the muscular extensor apparatus of the knee. However, in the co-pending application the femur section was provided with a shank for anchoring it in the thigh bone whose axis lay in the vertical, longitudinally extending centre plane of the recess between the pads or condylar members. As a result the patella, which is embedded in the patellar ligament, was unable to perform its natural movement downwards and inwards in an arc from its upper outward position without hindrance.

To form the knee-joint prosthesis according to the co-pending application in such a way that is is also possible for this natural movement of the patella to take place, the procedure in accordance with the invention is for the shank used to anchor the femur section to be secured to the yoke between the pads or condylar members of the femur section in a position where is it displaced away from the vertical, longitudinally extending centreplane of the recess between said pads towards the outer pad, and for this displacement to be adapted to the movement of the patella on the bearing face formed by the front face of the yoke between said pads and the front faces of said pads themselves, which bearing face is modelled on the natural human knee-joint, this movement taking place in an arc downwards and inwards in a sideways direction.

In this way it is possible during bending movements of the knee-joint for the patella to perform its natural sliding movement from an upper, outward positidn downwards and inwards in an arc into the recess between the pads or condylar members, since the inner part of the femur section is now further away from the axial plane of the anchoring shank than the outer part of the femur section, so that the patella thus slides into the recess between the pads of condylar members on the bearing surface which is formed by the yoke between the two parts of the femur section and the front faces of these two parts. By means of the invention the movement of the knee-cap in a healthy knee-joint is also achieved in a knee-joint prosthesis.

In order that the invention may be more clearly understood reference will now be made to the accompanying drawings which show one embodiment thereof by way of example and in which: Figure 1 is a side-view of the femur section of a prosthesis for the left kneejoint, Figure 2 is a plan view of the femur section from above, Figure 3 shows the femur section looking in the direction of arrow Y of Figure 1.

Figure 4 is a section on line 18 of Figures 2 and 3, Figure 5 shows the femur section looking in the direction of arrow X of Figure 1.

Referring now to the drawings, as in the co-pending application, the femur section of a knee-joint endoprosthesis comprises two pads or condylar members 13b and 13c which slide on the tibia section and which are yoked by an even surfaced part 14 at the front. The mutually adjacent faces of the pads or condylar members 13b and 13c are provided with guide grooves 15, which open upwards at one end, to engage a guide spigot in the tibia section, as in the copending application.

The front part of the yoke 14 and the front parts of the members 13b and 13c form a bearing face for the patella (not shown).

lo allow the movement of the patella to be matched to the natural patella movement, which takes place downwards and inwards in an arc from an upper outward position, the axis of the stem or shank 6 for anchoring in the thigh bone is displaced slightly outwards, towards the outer member 13c of the femur section and away from the vertical centre plane 17 which extends from front to rear through the gap 16 between the pads, into a vertical plane 18.

Since the inner member 13b of the femur section is now further away from the axial plane 18 than the outer member 13c, the patella can slide from an upper, outward position downwards and inwards in an arc into the recess 16 between the pads or condylar members on the front face of the yoke 14 and the front faces of the two members 13b and 13c, thus permitting a natural movement by the patella and thus preventing strain on the patella ligament or increased wear.

WHAT WE CLAIM IS: 1. A knee-joint endoprosthesis as claimed in claim 1 of U.K. patent specification No. 1,534,187, wherein the anchoring shank of the femur section of the joint is secured to the yoke between the pads or condylar members of the femur section in a position where is it is displaced away from the vertical, longitudinally extending centre plane of the recess between said pads towards the outer femoral pad and this displacement is adapted to the movement of the patella, which takes place in an arc downwards and inwards in a sideways direction, on the bearing face formed by the front face of the yoke between said pads and the front faces of said pads themselves, which bearing face is modelled on the natural human knee-joint.

2. A knee-joint endoprosthesis substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Figure 5 shows the femur section looking in the direction of arrow X of Figure 1. Referring now to the drawings, as in the co-pending application, the femur section of a knee-joint endoprosthesis comprises two pads or condylar members 13b and 13c which slide on the tibia section and which are yoked by an even surfaced part 14 at the front. The mutually adjacent faces of the pads or condylar members 13b and 13c are provided with guide grooves 15, which open upwards at one end, to engage a guide spigot in the tibia section, as in the copending application. The front part of the yoke 14 and the front parts of the members 13b and 13c form a bearing face for the patella (not shown). lo allow the movement of the patella to be matched to the natural patella movement, which takes place downwards and inwards in an arc from an upper outward position, the axis of the stem or shank 6 for anchoring in the thigh bone is displaced slightly outwards, towards the outer member 13c of the femur section and away from the vertical centre plane 17 which extends from front to rear through the gap 16 between the pads, into a vertical plane 18. Since the inner member 13b of the femur section is now further away from the axial plane 18 than the outer member 13c, the patella can slide from an upper, outward position downwards and inwards in an arc into the recess 16 between the pads or condylar members on the front face of the yoke 14 and the front faces of the two members 13b and 13c, thus permitting a natural movement by the patella and thus preventing strain on the patella ligament or increased wear. WHAT WE CLAIM IS:

1. A knee-joint endoprosthesis as claimed in claim 1 of U.K. patent specification No. 1,534,187, wherein the anchoring shank of the femur section of the joint is secured to the yoke between the pads or condylar members of the femur section in a position where is it is displaced away from the vertical, longitudinally extending centre plane of the recess between said pads towards the outer femoral pad and this displacement is adapted to the movement of the patella, which takes place in an arc downwards and inwards in a sideways direction, on the bearing face formed by the front face of the yoke between said pads and the front faces of said pads themselves, which bearing face is modelled on the natural human knee-joint.