Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2001-10-11
2003-12-30
Reip, David O. (Department: 3731)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S023150
Reexamination Certificate
active
06669734
ABSTRACT:
The invention relates to a femur shaft prosthesis which can be cemented in and which comprises a prosthesis neck, a shaft and a proximal centering apparatus which can be introduced with the shaft into a bone cavity.
Prosthesis shafts which can be cemented in and onto which proximal centering sleeves can be pushed on from distal are described in the patent application EP-A-0 962 197. These sleeves center the prosthesis shaft in the proximal region in the last phase of its insertion into a bone excavation which is filled up with still flowable bone cement. In a collar-less shaft the exact position along the shaft axis of a sleeve of this kind depends on the cone angle of the shaft in the proximal region and on the diameter tolerances of the sleeve and of the shaft. Prosthesis shafts frequently receive their outer shape through forging, which as a manufacturing procedure has a greater scattering with respect to the shaft diameter. The position of a sleeve which has hopefully been pushed on from the distal end in its correct rotational angular position with respect to the shaft axis fluctuates relatively strongly due to the increasing of the deviations in the axial direction which arise through a weak cone angle. If relatively coarse forging tolerances for the shaft diameter are also present, the axial position of the sleeve with respect to the shaft fluctuates to such an extent that it can no longer be used unconditionally as a height measure for the introduction depth in relation to the resection surface of a tubular bone.
The object of the invention is to create a selectively usable centering apparatus, the axial position of which is independent of the diameter fluctuations of the prosthesis shaft. This object is satisfied in accordance with the independent claim
1
in that the shaft is a collar-less shaft; in that the centering apparatus can be pushed from the medial onto the shaft in the cemented region and has at least in the medial region a centering wedge which widens towards the proximal and which is connected via webs to a clamping apparatus, with the clamping apparatus being arranged in the cement-less region of the prosthesis neck and being removable when the webs are interrupted.
This arrangement has the advantage that it is exactly positioned with respect to the neck region of the shaft, which is usually exactly machined in order for example to fix a ball head, and can thus also be used as a reference for the introduction depth. A further advantage consists in that the centering apparatus does not completely surround the shaft in the cemented region and permits the rising of surplus bone cement. A further advantage consists in that the region in which the centering wedge lies in contact at the shaft in the longitudinal direction can be made short and is limited to pressure zones of the normal loading, whereas in the remaining zones the still liquid bone cement can form a homogeneous, clearance-less pouch.
Subordinate claims
2
to
10
represent further developments of the invention.
Thus the removal of the clamping apparatus after the cementing in is facilitated if the webs have weak points which facilitate a severing or breaking off of the webs. Weak points of this kind advantageously lie at the transition to the centering apparatus in order that no residues project after the removal of the clamping apparatus. If the centering wedge itself consists of bone cement, for example of PMMA, then it can combine with the liquid bone cement at the locations which are wetted by the latter.
An economical manufacture of the centering apparatus results if it is manufactured of a plastic which can be processed on an injection molding machine. Knock out bores or a securing cone at the prosthesis neck are suitable as reference surfaces for the securing of the centering apparatus. An abutment which limits the sinking in of the shaft at the resection surface and which can later be removed can be formed with support surfaces which are anchored at the removable part of the centering apparatus.
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patent: 4938771 (1990-07-01), Vecsei et al.
patent: 5766262 (1998-06-01), Mikhail
patent: 5885295 (1999-03-01), McDaniel et al.
patent: 19518391 (1996-11-01), None
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patent: 0295360 (1988-12-01), None
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patent: 0393425 (1990-10-01), None
patent: 0738503 (1996-10-01), None
patent: 0962197 (1999-12-01), None
patent: 2041767 (1971-02-01), None
patent: 2687306 (1993-08-01), None
patent: 2042897 (1980-10-01), None
patent: WO 98/17207 (1998-04-01), None
Güttinger Werner
Spotorno Lorenzo
Sulzer Orthopedics Ltd.
Townsend and Townsend / and Crew LLP
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