GB2094634A

GB2094634A - Hip-joint prosthesis

Info

Publication number: GB2094634A
Application number: GB8131321A
Authority: GB
Original assignee: Schuett & Grundei GmbH; SCHUTT AND GRUNDEI GmbH
Current assignee: Schuett & Grundei GmbH; SCHUTT AND GRUNDEI GmbH
Priority date: 1981-03-14
Filing date: 1981-10-16
Publication date: 1982-09-22
Also published as: FR2501497A1; DE3109972A1; GB2094634B; JPS57153646A

Abstract

This invention relates to femur hip-joint endoprostheses of the kind in which the axis of the neck carrying the joint ball extends at an obtuse angle alpha to the longitudinal axis of the shank as seen in or against the direction of walking, whereas the plane which is inwardly (medially) and downwardly inclined of the collar bearing on the resection area and the longitudinal axis of the shank subtend an acute angle ss. According to the invention, the angle alpha is selected to be between 142 DEG and 148 DEG , the angle beta is selected to be between 62 DEG and 66 DEG and the medially measured angle gamma between the longitudinal axis and the collar plane is smaller than 90 DEG and is selected to be between 79 DEG and 83 DEG . In a preferred embodiment, the angle alpha is 145 DEG , the angle beta is 64 DEG , and the angle gamma is 81 DEG . <IMAGE>

Description

SPECIFICATION Improvements in or relating to femur hip-joint endoprostheses The present invention relates to femur hip-joint endoprostheses of the kind in which, as seen in or against the direction of walking, the axis of the neck carrying the joint ball extends at an obtuse angle ato the longitudinal axis of the shank, whereas the plane which is inwardly (medially) and downwardly inclined of the collar bearing on the resection area and the longitudinal axis of the shank subtend an acute angle ss. Hereinafter such endoprostheses will be referred to as "of the kind described".

In the case of endoprostheses ofthe kind described, as set forth for example in Aesculap brochure No. 113-C, 479/5, Edition VIII, page VI, it is known to increase the angle between the collar plane of the prosthesis which is to be brought to bear on the femur resection area, and a shank centre axis, so that the collar plane of the implanted prosthesis and the resection area of the femur neck are thereby brought closer to a horizontal position. To this end, the axis of the ball head neck extends at right angles to the collar plane orto the resection area, and the direction of the load applied by the body then passes through the thick cortitales of the calcar femoris, so that this internal, thick and loadbearing bone structure is axially loaded to exclude shearing stresses.

This known hip joint prosthesis is thereby deflected from the anatomical position of the thigh bone, since the position of the axis of the ball head neck at right angles to the collar plane orto the resection area has the result that the abductors, that is, the muscles acting externally on the femur, which must balance the weight of the body whilst the patient is standing on one leg, have an excessive length as compared to the neck of the prosthesis, so that these abductors allow the torso to bend towards the side of the playing leg which is unstressed, so that the direction of the load imposed by the body no longer passes through the internal load-bearing bone structure or does so only partially.In this case, the abductors would have to be tightened up surgically in accordance with the resulting shortening of the lever arm following the implantation of the endoprosthesis, to restore the balance of forces.

It is an object of the invention to adapt the femur hip joint endoprosthesis anatomically to the corporeal structure and in doing so to enable the hip joint endoprosthesis to be so matched to the anatomical length of the abductors that the weight of the body is held balanced by the abductors whilst standing on one leg, which situation recurs constantly whilst walking, to prevent an increased stress on the prosthesis and of its anchor seat, and a socalled hip collapse, meaning a drop of the loose leg side whilst walking.

Accordingly to achieve this and other objects, in an endoprosthesis of the kind described, the angle a is selected to be between 1420 and 1489 the angle,8 is selected to be between 620 and 66', and the medially measured angle ybetween the longitudinal axis and the collar plane is smaller than 900 and is selected to be between 790 and 830. The angle a may be 145 , the angle ,864 , and the angIey810.

In accordance with the invention use is made in particular of prosthesis shanks in accordance with the German Patent Specification No. OS 28 51 598, in which the axis of the shank, as seen against the direction of walking, is established by the longitudinal centre line of the lower shank section. Furthermore, the position of the resection area and of the collar surface of the prosthesis is displaced almost to the horizontal setting, but what is decisive in particular is that the axis of the ball head neck now no longer extends at right angles to the collar area, that is to say no longer steeply as in the case of known prostheses, but is inwardly tipped as compared to the aforesaid line at right angles, that is to say subtends a smaller angle than 900 with the collar area, namely between 790 and 830 and is preferably 81".

This causes an automatic adaptation of the prosthesis to the anatomical length of the abductors and thereby a perfect reception of the loading applied by the body by the abductors whilst the patient is stand- ing on one leg. At the same time, it is assured that the direction of the load applied by the body passes axially through the corticalis of the calcar femoris (that is, the internal bone structure which is very thick at this point), and the centre of the joint ball is brought closer to the shank axis, thereby preventing a tipping action on the prosthesis in the varus direction (meaning inwards), or largely avoiding the same.

In order that the invention may be more clearly understood reference will now be made to the single figure of the accompanying drawing which shows a view of a femur hip joint endoprosthesis as seen against the direction of walking.

Referring now to the drawing, a hip joint prosthesis in accordance with the invention comprises a shank 1 having the structure disclosed in the German Patent Specification No. OS 28 51 598. In this shank, the longitudinal axis 2, as seen against the direction of walking, is determined by the longitudinal centre line of the lower section of the shank 1.In accordance with the invention, the inwardly (medially) and downwardly inclined plane 3 of the collar 4 bearing on the resection area of the femur subtends an acute angle ss of the order of magnitude of 62t66 preferably of 640 with the longitudinal axis 2 of the shank, and the axis 5 of the neck 7 carrying the joint ball 6 subtends an obtuse angle a of the order of magnitude of 142t148 and preferably of 1450, with the said axis 2. In order that the object of the invention may be secured, the angle y between the longitudinal axis 2 of the shank and the collar plane 3 is selected to be smaller than 900 and lies between 790 and 830, preferably being 810. This accomplishes the advantages hereinabove referred to.

In conclusion, the direction 8 of the load applied by the body, which is transmitted via the prosthesis whilst standing on one leg, is indicated in the drawing.

Claims

1. An endoprosthesis of the kind described wherein the angle a is selected to be between 1420 and 148 , the angle ss is selected to be between 620 and 660 and the medially measured angle y between the longitudinal axis and the collar plane is smaller than 900 and is selected to be between 790 and 830.

2. A femur hip-joint prosthesis as claimed in claim 1, wherein said angle a is 1450.

3. A femur hip-joint prosthesis as claimed in claim 1 or 2, wherein said angle ss is 640.

4. A femur hip-joint prosthesis as claimed in claim 1, 2 or 3, wherein said angle yis 810.

5. A femur hip-joint prosthesis, substantially as hereinbefore described with reference to the accompanying drawing.