Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1993-02-01
1996-12-03
Isabella, David
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
623 18, 606 62, A61F 232, A61F 500
Patent
active
055803520
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to surgical prostheses and more particularly, relates to a femoral component for use in hip replacements either at first instance or in revision hip operations following an earlier implant failure.
Hip replacements are a common orthopaedic surgical procedure and are usually necessitated by degenerative disease of the hip joint, hip trauma or disease of the hip creating later hip trauma.
In a total hip replacement, the surgical procedure may involve reaming of the acetabulum, reaming of the proximal medullary cavity of the femur and inserting a prosthesis into the said medullary cavity to replace the natural femoral head.
The head of the prosthesis (usually formed by a detachable ceramic ball) mates with the acetabulum in the same manner that the natural femoral head mates with the acetabulum in a normal hip joint.
Depending upon the dictates of the pathology of the joint not all hip replacements require reaming of the acetabulum. In some cases only the femoral head requires replacement; for example, in a fractured neck of femur. The invention may be used in hemiarthroplasty or as the femoral component of a total hip arthroplasty.
There are in existence a number of hip prostheses which have been used to replace the femoral head. Whilst each of the prior art femoral head prostheses have enjoyed widespread use with varying degrees of success, each have suffered from certain attendant disadvantages.
One generally known and widely used prosthesis typically comprises an arcuate distal shaft having a gradual taper along its full length and terminating proximally in a neck which mates with the head of the prosthesis via a Morse taper. The shaft is inserted into the indra medullary cavity of the femur.
This prosthesis is fitted after the surgeon has reamed out the medullary cavity to an extent conducive to the production of tight interfitting between bone and prosthesis when the prosthesis is hammered into position. In practice, the reaming followed by sizing with the prosthesis may be carried out a number of times i.e., reaming followed by inserting the prosthesis until there is a small distance of travel of the shaft left near the neck of the femur to enable final hammering into position to thereby create tight interfitting between prosthesis and bone. In the final stages of this procedure, when the prosthesis is hammered home, care must be taken by the surgeon to avoid exploding the femur by creating hoop stresses beyond the modulus of elasticity of the bone. The tolerable limits of bone elasticity are guaged mainly by the experience of and feel by the surgeon.
Femoral explosion is one major drawback when using this prior art prosthesis both during insertion and extraction, however, explosion during insertion is largely due to poor surgical technique.
In the past, cementing of the prosthesis has also been employed, however, problems have existed with the use of cement. Failures in hip prostheses have occurred due to loosening at the cement bone interface and at the prosthesis bone interface. In some patients, a rotational failure of the prosthesis can be generated when a patient moves from a seating to a standing position.
Also, artificial hips may loosen and fail due to repetitive movement of the distal shaft induced by the locomotion of a wearer. This may eventually lead to a prosthesis failure and possibly unwanted axial dislocation; for example subsidence of the prosthesis.
One feature of the existing prostheses is a series of indentations which have been moulded into the distal shaft in order to encourage and stimulate bone growth therein. This bone ingrowth assists in holding the prosthesis firmly in position and also provides a keying and locking effect thereby lessening the possibility of rotational failure and/or unwanted axial subsidence of the prosthesis.
A further problem which exists with this type of prior art prosthesis and in particular with the distal shaft design is the difficulty in removal from the medullary cavity of a failed prosthesis. The procedure to replace
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patent: 4878916 (1989-11-01), Rhenter et al.
patent: 5019079 (1991-05-01), Ross
patent: 5259398 (1993-11-01), Vrespa
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