[Acetabular erosion after hip hemiarthroplasty. Clinical and biomechanical study].

Acetabular erosion is the most serious late complication of the hemiarthroplasty of the hip. We analyzed the factors influencing acetabular erosion after hemiarthroplasty for intracapsular femoral neck factures. Twelve patients of average age 71 years initially treated by one type of hemiarthroplasty in which conversion to total hip arthroplasty was performed due to pain and acetabular erosion. Evaluation was made of the interval between hemiarthroplasty and revision, indication for conversion and position of the head with regard to the apex of the greater trochanter. In case of a marked erosion of the acetabulum the evaluation included also the direction of the head migration. The basic group was further divided into two groups. The first group included 7 patients with an early revision, i.e. on average 22 months. The second group comprised 5 patients with a late revision at the average interval between the primary surgery and revision of 68 months. High position of the prosthetic head was found out in all patients of the first group while neutral or low position was recorded in all patients of the second group. In 7 cases with marked acetabular erosion we reconstructed the direction of the prosthesis migration. We recorded three directions of migration of the prosthetic head--proximomedial, purely proximal and proximolateral. The direction of migration depended on the position of the head, CE angle and position of the prosthetic stem in the medullary canal. The resection level of the femoral neck and resulting from it the position of the prosthetic head is a significant factor influencing the progress of acetabular erosion.