A - Human Necessities – 61 – F
Patent
A - Human Necessities
61
F
3/104
A61F 2/36 (2006.01) A61F 2/32 (2006.01) A61F 2/00 (2006.01) A61F 2/30 (2006.01) A61F 2/34 (2006.01) A61F 2/46 (2006.01)
Patent
CA 1097452
TOTAL HIP JOINT REPLACEMENT Abstract of the Disclosure In the replacement of the hip joint, full access to the hip joint is obtained by separating the trochanter, a large protruberance on the upper portion of the upper leg bone, or femur, from the remainder of the femur; and the subsequent dislocation of the hip joint. Following dislocation, a minimum amount of bone is removed from the femoral ball and sufficient bone is removed from the socket to accommodate the minimum thickness surface replacement elements. A thin hollow inert metal ball or shell member having an outer diameter close to that of the original hip joint is then cemented onto the upper end of the femur, and an ultra high molecular weight polyethylene cup is cemented into the hip bone socket, with acrylic bone cement. The metal shell is designed for securing to bone surfaces prepared with precision reaming techniques. To achieve maximum strength with minimum thickness, both the metal and plastic surface elements, although spherical at their mating surfaces, are thicker at their maximum load bearing points toward the top, and are of lesser thickness elsewhere. The two joint surface elements which are both generally hemispherical, have inner and outer surfaces which are both eccentric and asymmetric, with the thicker portion of the plastic liner being about 45° of the central hemispherical axis, and the thicker portion of the metal shell being its upper portion. A clearance of 0.1 to 0.3 millimeters is provided between the metal shell and plastic liner, and the plastic liner is provided with a relieved and contoured inner face to permit maximum range of movement of the joint. The thickness of the plastic socket is selected to accommodate the variable possible amount of bone removed from the hip socket as needed to provide healthy solid bone support for the cup shaped member and adequate plastic liner thickness to provide the required strength. Following cementing of the metal and plastic joint surfacing elements into place, the joint is relocated in position, and the trochanter is wired back into position on the femur.
295871
Amstutz Harlan C.
Clarke Ian C.
Smart & Biggar
University Of California
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