High failure rate of soft-interface stem coating for fixation of femoral endoprostheses

Twenty-five total hip arthroplasties were performed in 25 patients using a femoral stem with a soft-interface coating of Proplast (Vitek, Houston, TX). Follow-up periods for 24 of the hips ranged from 82 to 104 months (median, 96 months). Fourteen (58%) of the hips were judged to be failures, and nine of the failures were revised. The prostheses were thought to have failed because the coating was not strong enough to withstand normal weight-bearing loads. This inner-substance failure of the coating was seen in all revision operations. During these revisions, parts of the coating remained in the shaft as well as on the prosthesis stem. The combination of clinically manifest midthigh pain and radiologic scalloping and/or the pedestal sign seem to justify a strong suspicion of looseness of this type of cementless femoral endoprosthesis.