Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1994-09-19
1996-11-05
Weiss, John G.
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
623 18, A61F 232
Patent
active
055712029
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
This invention concerns a shank or shaft for an articulation or joint-endoprosthesis and a component of a joint-endoprosthesis with such a shank.
BACKGROUND OF THE INVENTION
Joint endoprostheses, especially for hip-joints, consist of an acetabular shell component and of a femur component insertable by its shank into the tubular femur.
Femur components for hip prostheses already are known that consist essentially of a metal core and a surrounding plastic sheath. This design offers the advantage of behaving similarly elastically to the bone structure to be replaced.
However, this kind of femur component entails the problem of an unprotected sheath polymer surface from which residual monomers may be released to possibly form a thin reticular bonding layer between the plastic sheath and the bone.
SUMMARY OF THE INVENTION
An object of the invention is to provide a shank for a joint-endoprosthesis which on one hand offers improved elastic behavior matching the physiological needs of the bone in such a way that the shank flexibility, when subject to bending, approximates that of the natural bone and allows gradual load transfer from the shank to the enclosing bone, and on the other hand offers improved biocompatibility. Furthermore, the invention solves the problem of endowing a joint-endoprosthesis with improved surface hardness.
Essentially, the advantages of the invention are that, thanks to the surface layer of the invention, the shank bio-compatibility is improved as a whole and that direct and firm contact between the shank and the bone is made possible. Depending on the kind of bio-compatible surface layer, bone growth can be induced, thereby improving the primary stability, that is the initial anchoring, and thus accelerating the healing stage.
In a preferred embodiment of the invention, the shank is fitted with one or more boreholes in the proximo-lateraI area, that is at the outer side of its upper end. These boreholes serve to anchor by screws the prosthesis shank in the proximal area of the outer cortex. Such a screw may be rotated from above, that is from the side of the prosthesis neck, i.e., from the prosthesis collar, through the borehole laterally into the bone where it is thereby anchored. However, the borehole also may be internally threaded and the screw may be rotated from below, that is laterally into the inner thread, the resting surface of the screw on the outer cortex being enlarged as called for by using a washer. On one hand these screws enhance security against shank rotation inside the marrow duct and on the other hand they contribute synergistically together with the triple-layer design of the prosthesis shank of the invention to a gradual load transfer from the shank to the bone.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention and further developments thereof are elucidated below with reference to an illustrative embodiment.
FIG. 1 is a longitudinal section of a shank of the invention inserted in a thighbone;
FIG. 2 is a cross-section along line A--A of the proximal portion of the shank of FIG. 1;
FIG. 3 is a cross-section along line B--B of the distal portion of the shank of FIG. 1;
FIG. 4 schematically shows the surface layer of the shank of FIG. 1 for the illustration of a particulate layer when this surface layer consists of a uniform material; and
FIG. 5 schematically shows the surface layer of the shank of FIG. 1 when it is a particle layer of compound nature.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The femur component of a hip-joint prothesis shown in FIGS. 1-3 essentially consists of the triple-stratum shank 1, 2, 3 of the invention which continues into a conical neck part 10 that can receive a plug-on swivel ball 12. As regards other types of hip-joint protheses, the swivel joint also may be rigidly affixed to the neck part 10 and form one unit with the shank.
The sandwich-type shank 1, 2, 3 consists of a titanium or titanium-alloy core 1 imbedded in a biocompatible, thermoplastic (for instance POM, PEEK, PEI or the like) sheath 2. The two m
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Gasser Beat
Mathys, Jr. Robert
Mathys, Sr. Robert
Farley Walter C.
Mathys AG Bettlach
Snow Bruce E.
Weiss John G.
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