Total hip arthroplasty with a low-modulus porous-coated femoral component

Fifty-seven patients had sixty-three total hip replacements, performed using a femoral stem with a soft, low-modulus porous coating of Proplast and a conventional acrylic-cemented acetabular component. Forty-seven of the hips were followed for an average of thirty-seven months. Seventeen (36 per cent) of the forty-seven hips were judged to be clinical failures, and five of the failures were revised by inserting a new femoral component and fixing it with acrylic cement. The prostheses were thought to have failed because they had inadequate support, due to deficiencies in the design of the stem and in the fit of the implant in the femur. The five retrieved prostheses were found to have fibrous-tissue ingrowth into the coating, which had failed by shear within its substance. Therefore, we concluded that the coating had insufficient strength to withstand normal weight-bearing loads. To improve performance, a more stable prosthesis with a stronger porous coating is needed. In addition, a posterior surgical approach through a transtrochanteric osteotomy may give better exposure of the femoral canal and facilitate the use of longer-stem (140 to 153-millimeter) designs, which are less likely to be inserted in a varus position.