A radiographic study of hip-joint alignment after prosthetic hip arthoplasty.

Postoperative hip alignment was studied on radiographs in cases of total hip arthroplasty (THA) and of Bipolar Head Prosthesis(BHP), both with MX-1. Postoperative anteroposterior-view radiographs of hip joints of patients with a normal hip joint on the unoperated side and without pelvic tilt were used. Thirty-nine THA patients (femoral neck fracture), 26 THA patients (osteonecrosis of the femoral head and osteoarthritis of the hip joint), and 34 BHP patients were selected for this study. Lines and points for measurement of 9 parameters were established on radiographs. The position of the greater trochanter upper edge is 6.5 mm (mean) superior to the femoral head center in the normal hip joint of Japanese, unlike in Caucasians. A femoral head prosthesis should be inserted so that its center and the greater trochanter upper edge are level in order to equalize leg lengths. In BHP cases, the insertion is made so that the greater trochanter upper edge is approximately 4-mm superior to the center of the prosthesis. For further securing of the stem and to equalize leg lengths, stems should be available in 11 diameters from 5-15 mm in 1-mm increments. Postoperative hip alignment in MX-1 THA cases was found to be satisfactory.