Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1999-01-12
2001-03-20
Mancene, Gene (Department: 3732)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
Reexamination Certificate
active
06203575
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a modular system with a mounting apparatus for the mounting of shaft prostheses.
2. Description of the Prior Art
FR-A-2 727 857 shows a shaft prosthesis for a shoulder joint which consists of a stem and a prosthesis head which are connected to one another via a fixable ball joint. The prosthesis head consists of a shallow spherical section, the underside of which is to lie on a planar resection surface of a humerus in order to completely cover off the resection surface. A spherical body which stands off from the stem in an inclined direction to the stem axis is divided up by slits into lobes which can be spread apart by a thorn which is driven into the spherical body through the stem in the inclined direction. In the prosthesis head a spherical bearing shell is worked in from the lower side which encloses the spherical body during the spreading apart and blocks it at a selectable angle to the stem axis. A disadvantage of this arrangement is that this setting of the inclination must be done in advance and that a considerable spatial imagination is required of the surgeon. Since the dimensions of the fixable ball joint must be kept small for reasons of space, a plastic deformation at the feet of the lobes is compulsory during their fixing and self inhibition is necessary in a spreading thorn for safety. This means that, with all the other advantages of this construction, the surgeon actually has only one chance in order to definitively fix the coupling.
SUMMARY OF THE INVENTION
The object of the invention is therefore to achieve a precise pre-setting of a shaft prosthesis of this kind. This is achieved by a modular system with a mounting apparatus comprising shaft prostheses which can be assembled from stems of different sizes and prosthesis heads of different sizes, with a fixable coupling existing between the stem and the prosthesis head which allows different positions and angular orientations between the prosthesis head and the stem; comprising test prostheses which can be assembled in different sizes analogously to the shaft prostheses and which have a releasably fixable coupling which can be fixed in the test prosthesis which is inserted in a bone in order to hold firmly an ideal position and angular orientation of the head of the test prosthesis with respect to its stem, which after the removal of the test prosthesis can be transmitted with the latter to the mounting apparatus in order to mutually fix a stem and prosthesis head corresponding to the test prosthesis in the mounting apparatus in the position and angular orientation of the test prosthesis.
An advantage of this arrangement consists wherein, through the modular system principle, fewer parts in the prostheses and test prostheses are required in order to cover a wide spectrum. A further advantage consists wherein the test prosthesis is movably journalled relative to the stem with its head during the insertion in order to bring the head into the most favorable position with respect to the resection surface and the articulation. The position of the head can be fixed in the state of insertion into the bone and its function tested. When the stem of the test prosthesis is inserted the head can be replaced, the new head oriented and fixed, and its function tested. The surgeon has the assurance that the shaft prosthesis which is later inserted will fulfil its function equally well.
Use of the modular system is favorable for shoulder joints, which have a comparatively low loading and therefore allow fixable ball joints as a coupling from the stem to the head. The bearing shell is arranged in the prosthesis head and has the same position relative to the lower side in spite of the different outer dimensions of the head. Through a radial displacement from the center of the bearing shell to the central axis of the head, the latter can be changed in its distance from the stem axis through rotation and can thus cover a wider spectrum of resection surfaces which are displaced differently with respect to the stem axis.
An advantageous mounting apparatus results from the fact that it has first reception apparatuses by means of which every stem size can be positioned and clamped in a unique and reproducible manner, and that it has at least one second reception apparatus which, guided, is displaceable relative to the first reception apparatuses and can be guided after a test prosthesis which is clamped in the first reception apparatus into a unique angular orientation and position of the head and fixed there in order to mutually orient and combine an equally large stem and an equally large test prosthesis in the same position and angular orientation after the removal of the test prosthesis.
A mounting apparatus of this kind can be used not only for the setting of shaft prostheses in accordance with test prostheses which have been tested in their function. They also permit, in the event of fractures of the bone which make test prostheses impossible, the setting of the shaft prostheses at a predetermined angular orientation, for example, at an intermediate angle between a coupling axis parallel to the central axis of the head and a stem axis of 130°, and a retro-torsion to the left or the right of 18°.
Instead of a floating disc which is journalled in a coupling, a fixable Cardan joint can also be used in a mounting apparatus of this kind. The second reception apparatus must basically be constituted in such a manner that it can follow the adjustment movements which are possible through the coupling.
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Mancene Gene
Robert Eduardo C.
Sulzer Orthopaedie AG
Townsend and Townsend / and Crew LLP
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