Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1987-01-08
1988-12-20
Frinks, Ronald L.
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
623 16, 623 18, 128303R, 128 92VT, A61F 236, A61F 228, A61F 230
Patent
active
047923393
DESCRIPTION:
BRIEF SUMMARY
This application corresponds to application PCT/EP85/00251 filed May 23, 1985 under the provisions of the Patent Cooperation Treaty and the benefit of the priority of said application is claimed.
This invention relates to a self-locking stemmed component for a joint endo-prosthesis, in particular for the femoral component of a hip joint prosthesis.
BACKGROUND OF THE INVENTION
Twenty-plus years of lively development in hip joint prosthesis design have not produced a fully satisfactory solution to the problem of stem loosening; it still is a major long-term complication. Current trends towards bone integration are addressing only some, perhaps minor problems of prosthesis-bone interaction.
A femoral component for an artificial hip joint is known from the German Offenlegungsschrift no. 31 13 898 in which the stem is formed by several anchoring rods which together with a collar are made from one solid casting. The rods are pressed against the inside of the bone by plugs, thereby producing a locking effect. A fixation system of this kind is not only difficult and time-consuming to insert but produces still an uncontrolled, uneven load transfer from the stemmed component of the joint endo-prosthesis to the bone with high load concentrations at the end of the stem.
SUMMARY OF THE INVENTION
The invention as claimed is intended to provide a remedy. It solves the problem of how to design a true self-locking stemmed component that can be easily inserted and removed if necessary and whose load transfer from the stem to the inner cortex of the medullary canal of a tubular bone is evenly distributed in a controlled manner. It accordance with tee invention there is provided a self-locking stemmed component for a joint endo-prosthesis whose stem thickness tends to increase when said stemmed component is loaded by physiological loads. A self-locking stemmed component in accordance with the invention is distinguished from the known constructions by its optimal adaptability to the medullary canal of the tubular bone, the ability of the stem to transmit indipendently the specific compressional, respectively tensional forces prevailing at the respective interfaces between stem and cortex in a controlled manner and as gradually and evenly as desired and the ease of its removal. Bending stiffness of the stem, a major obstacle to controlling the load transfer, is reduced manyfold by the stem geometry according to the invention.
The self-locking stemmed component consists preferably of two lobes, one for transfer of compression loads and the other for transfer of tension loads. The two lobes are destined to be pressed against the inner walls of the medullary cavity of a tubular bone by the action of connecting structures interconnecting said two lobes in such a way that relative axial displacement between said two lobes, as produced upon bending of said self locking stemmed component, increases the distance between said two lobes. The pressure for holding the two lobes in place is therefore generated by said connecting structures which are acting as wedges when the stemmed component is loaded and said two lobes are displaced in there relative axial position.
BRIEF DESCRIPTION OF THE DRAWING
In the drawing
FIGS. 1(a) and 1(b) are schematic views of a stem section according to the state of the art;
FIGS. 2(a) and 2(b) are schematic views of a stem according to the invention;
FIG. 3 is a sectional view of a femoral component for a hip joint prosthesis consisting of a self-locking stemmed component according to the invention and a joint head;
FIG. 4 is a sectional view of an implanted state-of-the-art femoral component of a hip joint prosthesis;
FIGS. 5 and 5(a) are respectively, a sectional view of an implanted femoral component according to the invention and a cross-sectional view of the stem taken along the line I--I;
FIGS. 6(a) and 6(b) are magnified sectional views of the femoral component of FIG. 5 showing the effect of insertion;
FIGS. 7(a) and 7(b) are respectively, a sectional view of a femur and a sectional view of
REFERENCES:
patent: 4292695 (1981-10-01), Koeneman
patent: 4306550 (1981-12-01), Forte
patent: 4314381 (1982-02-01), Koeneman
Frinks Ronald L.
Laboratorium fur Experiementelle Chirurgie, Forschungsinstitut
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