Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1990-01-12
1991-04-02
Frinks, Ronald
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
623 16, A61F 236
Patent
active
050044753
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a femoral hip prosthesis in general and more particularly to a stem for a femoral prosthesis which can be arranged in the femur without cement.
BACKGROUND AND SUMMARY OF THE INVENTION
Visible in the metaphysis of a normal hip is a pattern of support and traction trabeculae, which pattern corresponds with the pattern of mechanical forces. In the course of extensive research a prosthesis has been developed possessing a form such that the natural bio-geometrical forces pattern is approximated as closely as possible in the femur metaphysis. In other words the femoral prosthesis must be arranged in the femur such that during loading the centre of gravity of the femoral prosthesis lies as closely as possible to or coincides with the metaphysial centre point.
FIGS. 5, 6 and 7 in the drawing are femur sections showing different supporting possibilities of the femoral prosthesis, whereby for the sake of clarity the contact surfaces are shown enlarged and shaded.
In FIG. 5 the prosthesis 2 arranged in the femur 1 supports medially on the pubic arch ("Adamse boog") S.sub.1 and laterally on the cortex S.sub.2. In the case of unipodal loading G of the hip head 3 the centre of gravity CG will come to lie during the resolution of forces very close the pubic arch S.sub.1 and at a large interval from the metaphysial centre CM. The overpressure created at the pubic arch S.sub.1 has to be compensated by for instance a flange supporting against the greater trochanter 4.
In the situation shown in FIG. 6 the prosthesis 2 supports medially on the pubic arch S.sub.1 and laterally on the greater trochanter S.sub.3. When unipodal loading G occurs the centre of gravity CG is located in the neck 5 of the prosthesis and once again at an interval from the metaphysial centre.
FIG. 7 shows the ideal loading according to the invention, whereby the prosthesis 2 supports medially on the pubic arch S.sub.1 and laterally on the lateral cortex S.sub.2 and the greater trochanter S.sub.3. In the case of unipodal loading G the centre of gravity CG and the metaphysial centre CM now coincide. It is the loading shown in FIG. 7 which is approximated as closely as possible with the prosthesis according to the invention.
It is noted that the loadings of the femur 1 shown in FIGS. 5-7 have been confirmed in mechanical loading experiments with plastic prosthesis elements, whereby, using polarised light the forces/loading pattern was visualised.
The invention relates to a stem for a hip prosthesis and the hip prosthesis itself, which stem is provided for medial support on the pubic arch (S.sub.1) with a curved, smooth medial stem support part, is provided for lateral support on the lateral cortex (S.sub.2) with a lateral stem support part, and is provided for lateral support on the greater trochanter (S.sub.3) with a lateral comb-like stem support part located between the lateral stem support part and the head end and comprising a number of combs, the comb connecting onto the lateral side protruding laterally relative thereto, and which stem is provided on the ventral and dorsal side at the point of the metaphysial portion with at least one groove which consists of groove portions converging in the direction of the head end and enclosing an apex. Achieved through this manner of supporting is that the centre of gravity of the prosthesis coincides with or lies in the direct vicinity of the metaphysial centre, and in this way duplicates as closely as possible the natural bio-geometrical forces in the femoral metaphysis.
For the lateral supporting on the greater trochanter S.sub.3 it is favourable that the comb-shaped stem support part comprises a number of combs and that the comb connecting onto the lateral side protrudes laterally relative thereto. This comb-like structure for the stem support part prevents a distal sliding of the prosthesis when loading occurs, after ingrowth into the bone of the greater trochanter, while in addition excessive loading of the lateral cortex S.sub.2 is countered and therefore the rotation
REFERENCES:
patent: 4031571 (1977-06-01), Heimke et al.
patent: 4310931 (1982-01-01), Muller
patent: 4659067 (1987-04-01), Fournier
patent: 4714470 (1987-12-01), Webb, Jr. et al.
patent: 4728334 (1988-03-01), Spotorno
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