Prosthetic position in total hip replacement.

The AP radiographs of 230 total hip replacements were studied to determine how often the prostheses were correctly positioned. It appeared that the inclination of the prosthesis was less important than the position of the center of rotation of the arthroplasty. A new method of measurement was applied to the preoperative and postoperative radiographs of 85 patients with unilateral hip disease and no previous operations. Correction of migration of the center of rotation of the arthritic hip, coverage of the center of rotation, and leg length were determined and related to the function of the arthroplasty. The method emphasizes the importance of the center of rotation and answers the questions: Does the design of the prosthesis allow the center of rotation to be placed in the desired position and did the surgeon place the prosthesis in such a position?