Middle-term results of anatomic medullary locking total hip arthroplasty

We report the results of cementless, anatomic, medullary locking hip prosthesis application in our first consecutive series. We used the so-called Asian size of prosthesis with proportionally smaller stem sizes in both diameter and length. Forty-seven stems and sockets were analyzed with a mean follow-up of 69 months. The mean Merle d'Aubigné hip scores were 8 points preoperatively and 16 points at the final follow-up. Radiologically, the stems showed excellent stability without loosening. Stress shielding around the stems did occur in most cases but did not progress. Preoperative bone quality influenced the extent of stress shielding evaluated at the final follow-up: higher stress shielding was noted in poorer quality bones at the time of operation. There were problems with the sockets. The shallow socket and impingement at the protruded rim seemed to cause a high incidence of dislocation (13%). Massive polyethylene wear occurred in 5 sockets. These sockets were 48 and 46 mm in diameter with 26 mm heads. In conclusion, the stems of the anatomic medullary locking hip prostheses used in Japan showed satisfactory stability even in poor quality bones, but there were problems with the polyethylene liners. Our solution was to use larger sockets with 22 mm heads.