Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1996-09-18
2000-05-09
Yu, Mickey
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
623 23, A61F 232, A61F 236
Patent
active
060598336
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a hip cup for use as an acetabular component in a hip prosthesis, comprising a shell part having an at least partially convex outer surface, which shell part can be inserted in a cavity having an inner surface that is substantially defined by the outer surface of a segment of a sphere.
The two techniques that are used most for attaching a hip cup concern the cemented and the uncemented technique respectively. In the cemented technique, the hip cup is fixed by means of bone cement. Within the uncemented technique, screw hip cups and press-fit hip cups are used. Screw cups are screwed into a cavity, which may or may not have been provided artificially in a bone, press-fit hip cups are for instance attached by knocking the hip cup into place in such cavity.
With these methods an attempt is made to approach the original anatomic situation as much as possible through the proper positioning of the acetabular component in the acetabulum. The position of the press-fit hip cup will change slightly in the first few months after positioning, due to the forces applied thereto. This change of position is commonly referred to as "settling".
For applying hip prostheses in patients, it is known to provide in an acetabulum a cavity having a truly spherical inner surface by means of a spherical cutter, wherein, subsequently, a press-fit hip cup is fittingly provided. Hence, this involves the outer surface of the hip cup abutting completely against the inner surface of the cavity formed, as a consequence of which, directly after the positioning of the hip cup, the forces acting on the hip cup are completely distributed on the inner surface of the cavity. The forces applied to the hip cup by the patient, particularly during movements of his leg, will cause the hip cup to slightly change position, especially in the first few months after positioning. Because the bone tissue around the hip cup will not have healed entirely yet in those months, and the hip cup will hence not have integrated entirely in the acetabulum yet, the hip cup will still be capable of moving somewhat, so that space will be created around the longitudinal edge of the hip cup. As the hip cup rests against the apex, it cannot be pressed any further into the cavity and will therefore become increasingly looser due to a cranial displacement, with all its consequences, in particular with regard to the patient's mobility. Moreover, this will cause the occurrence of high local peak loads.
SUMMARY OF THE PRESENT INVENTION
Hence, the object of the invention is to provide a hip cup of the type described in the opening paragraph, wherein the settling of the hip cup after positioning remains possible in an advantageous manner, without involving the occurrence of the above-mentioned peak loads and changes of position. To this end, the hip cup according to the invention is characterized in that the outer surface of the shell part substantially corresponds to the outer surface of a part of an ellipsoid, the arrangement being such that during positioning, the shell part contacts the longitudinal edge of the cavity at least by a circumferential edge, while a space is formed between the inner surface of the cavity and the apex of the shell part.
As the hip cup has an ellipsoid outer surface, it can be disposed in a spherical cavity with space, while a circumferential edge contacts the longitudinal edge of the cavity. As a result, when the hip cup is loaded in the first few months after positioning, the hip cup can advantageously be pressed somewhat further into the cavity, while the part of the convex outer surface of the hip cup that is contacted with the concave inner face of the cavity will become larger and larger. Due to the nature of the change of shape of the cavity and the shape of the hip cup, the transmission of forces from the hip cup to the acetabulum will largely be distributed on the periphery of the hip cup, as a result of which load peaks are avoided. Because the hip cup according to the invention has
REFERENCES:
patent: 4666448 (1987-05-01), Ganz
patent: 4878916 (1989-11-01), Rhenter et al.
patent: 4878946 (1989-11-01), Rhenter et al.
patent: 5021062 (1991-06-01), Adrey et al.
patent: 5171285 (1992-12-01), Broderick
patent: 5226917 (1993-07-01), Schryver
patent: 5549695 (1996-08-01), Spotomo et al.
Endocare AG
Stewart Alvin
Yu Mickey
LandOfFree
Elliptic acetabular component for a hip prothesis does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Elliptic acetabular component for a hip prothesis, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Elliptic acetabular component for a hip prothesis will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1060211