Failure mechanisms of anatomic porous replacement I cementless total hip replacement.

The APR-I Hip System was designed for metaphyseal bone attachment by proximal patch porous coating and the acetabular component was a hemisphere fixed with screws. The results of 100 consecutive primary total hip arthroplasties performed with the APR-I were studied in patients still alive after an average of 6.7 years. The selection of hips for implantation of this hip system was limited to those patients in whom a satisfactory intraoperative fit could be obtained. This resulted in a distribution of patients such that 75% were younger than age 65 years and only 15% had osteoporotic bone. The revision rate was 16% with a mechanical failure rate of 11%. Seventy percent of hips had progressive loss of fixation. loss of femoral component fixation was correlated with younger patient age, higher patient activity level, metaphyseal fill of less than 90%, and increased polyethylene wear and osteolysis. Eighty-nine percent of hips maintained femoral neck contact with the porous coated collar. The acetabular component was well fixed in 97% of hips. The failure rate of the APR-I stem is unacceptably high and this stem is no longer used by the authors.