Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1998-01-07
1999-07-27
Willse, David H.
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
606 91, 623 18, A61B 1758, A61B 1716
Patent
active
059282878
DESCRIPTION:
BRIEF SUMMARY
For implanting acetabular cup endoprostheses into the acetabulum, which may optionally have been provided with a bed of cement, instruments are normally used which have, at the end of a gripping rod, a holding head which, for the purpose of holding the cup in a predetermined relative position to the instrument, has a block, engaging in the matching cavity of the cup, and a collar which bears on the edge of the cup. The force necessary for pressing the cup into the acetabulum can thereby be transmitted easily to the cup. However, it is desirable that the cup is also held securely on the instrument in the opposite force direction and in the direction of rotation, and that it can be released from the instrument again without transmitting appreciable forces.
For this purpose, a known implantation instrument (FR-A-2,721,502), on which the wording of the preamble of claim 1 is based, has a block which grips in the acetabular cup and which is adapted exactly to the shape of the opening forming the cavity, and holding pins which are arranged axially parallel on the collar and engage in holding openings which are designed as axially parallel bores on the front face of the acetabular cup. The latter is held on the instrument via the block and the holding pins by means of frictional forces. For its removal, a plunger which is axially displaceable counter to a spring force by means of an actuating member forces the instrument off from the acetabular cup. The disadvantage is that the acetabular cup is held on the instrument only via the unreliable frictional engagement, which has to be made very powerful so that the desired holding force is obtained even in the event of the coming-together of most unfavourable tolerance deviations. For release, a comparatively great force, overcoming the holding force, must be applied, generally greater than the desired holding force. The greater the force that has to be applied for release, the more difficult it is to hold the instrument steady.
An implantation instrument which likewise holds the prosthesis by frictional force is known from U.S. Pat. No. 5,169,399. This comprises a head which is adapted to the shape of the cavity of the acetabular cup and whose halves are pressed away from each other and against the inner wall of the acetabular cup by a spring force. To release the instrument from the acetabular cup, the halves of the head are moved towards each other using an actuating lever, so that the contact with the acetabular cup is eliminated. In view of the low coefficient of friction of the inner face of an acetabular cup, the force with which the halves of the head of this implantation instrument are pressed against the inner face of the acetabular cup, and which has to be applied as releasing force when removing the instrument, must be greater than the desired holding force. The disadvantages of this device therefore correspond to those mentioned above. In addition to this, there is only unsatisfactory protection against unwanted turning of the acetabular cup on the instrument.
In the case of another known implantation instrument (WO94/21199), radially arranged holding projections engage in holding openings on the inner side of the acetabular cup. An intermediate piece is attached to the instrument, the latter having a block fitting with centering in an opening in the base of the prosthesis, on which intermediate piece there are holding projections which are movable transverse to the opening direction, engage with a spring force in the holding openings, and can be withdrawn from these by means of an actuating member. This arrangement is disadvantageous because the openings in the inner face of the prosthesis are generally undesirable and demand a greater wall thickness of the prosthesis at an anatomically unfavourable location.
For the purpose of holding acetabular cup reamers, instruments are known (U.S. Pat. No. 5,171,313, FR-2,281,095) which engage with radially arranged holding pins in openings on the inner side of a reamer head and which can be withdrawn counter to a
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Jackson Suzette
Waldemar Link (GmbH & Co.)
Willse David H.
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