Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1994-05-02
1998-09-01
Willse, David H.
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
606 65, A61F 236
Patent
active
058005536
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a hip joint prosthesis intended to be permanently anchored in the human hip joint and more specifically to the part of the hip prosthesis which is to be anchored in the femur or thigh bone of the patient and which comprises an attachment part for a ball unit designed to be anchored in the neck of a human femur (collum femoris), said attachment part comprising an elongate anchoring element or primary fixture intended to be inserted into a channel bored and extending through the femoral collum from the outside of the femur, and a secondary fixture intended to be attached to the collum after removal of the head of the collum, said primary fixture and said secondary fixture being provided with means for connecting said fixtures to each other.
BACKGROUND OF THE INVENTION
The present invention is a development of a hip joint prosthesis of the kind disclosed in WO 89/11837. This document thus inter alia discloses a hip joint prosthesis comprising a primary fixture in the shape of a sleeve, said sleeve being intended to be inserted into a central hole bored longitudinally through the collum femoris from the outer side of the femur and a secondary fixture in the shape of a cap having a spherical shape intended to be attached to and cover the end of the collum femoris when the head of the collum has been removed partly or entirely and the outside of remaining end has been cut to a cylindrical shape. The primary and the secondary fixtures are interconnected by means of a bolt which at one end has an internal thread. The bolt is to be inserted into the sleeve and its internal thread is to be made to engage a central, threaded stud projecting from the spherical cap. When the bolt is tightened, the cap is pressed over the cylindrically cut shape of the end of the collum.
In some applications it is however not suitable to use this prior art device. One reason for this is that the shape of the collum may make it difficult to retain enough cortical bone to give the secondary fixture or cap a firm support, since the shape of the collum may vary greatly. Another reason is that it in some cases may be important to achieve an exactly defined compression of the cortical bone, i. e. that a clearly defined pressure is exerted onto the collum from the secondary fixture irrespective of how the secondary fixture is attached to the primary fixture.
Other similar prior art is disclosed for instance in DE-A1-28 45 231, DE-A1-27 24 040, U.S. Pat. No. 4,795,473 and U.S. Pat. No. 4,005,495.
BRIEF DESCRIPTION OF THE INVENTIVE CONCEPT
According to the invention a hip joint prosthesis of the kind described above is designed with the length of said primary fixture being chosen such that said primary fixture ends close to the head of the collum, said secondary fixture comprising a plug-like part intended to be inserted in a cylindrical countersunk cavity cut into the cancellous bone of the collum and extending to the cortical bone in at least three locations, the size of the secondary fixture being chosen such that the fixture abuts the cortical bone of the collum in at least said three locations.
This will entail that the cortical bone will remain intact to a larger degree and that the load conditions will be such that a physiologically appropriate load on the upper part of the collum can be achieved. Forces can be transferred without any noticeable movements between the implant (secondary fixture) by means of the direct bone contact on the inside of the cortical bone in the collum.
The expansion bolt, which is an preferred embodiment of the means for attaching the primary fixture to the secondary fixture, will also ensure that the primary fixture, which mainly will be located in the cancellous bone in the collum and which therefore may sag to some extent in the above prior art device, is supported in a better way along its longitudinal extent by the secondary fixture. The expansion bolt will also give a connection which is so stiff that fretting corrosion between the pa
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Albrektsson Bjorn
Carlsson Lars
Jacobsson Magnus
Rostlund Tord
Wennberg Stig
Aktiebolaget Astra
Willse David H.
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