Fit with the proximal femoral cortices is critical to the success of cementless femoral stems in total hip arthroplasty. Conventional femoral stems are often designed from the average geometry of the normal femora. Hip disease in Japan, however are predominantly associated with Osteoarthritis secondary to congenital hip dislocation or sublux-ation of the hip. We developed a new model of proximal fitting cementless total hip stem, the so-called FMS (for Fukui Medical School) stem, based on the endosteal geometry of Japanese proximal femoral canal with developmental dysplasia of the hip. The proximal third surface of this stem model was circumferentially hydroxyapatite-coated.

One hundred-two hips in 85 patients underwent cement-less total hip arthroplasty with the new stems were studied with a minimum follow-up period of two years. There were 78 women and 8 men, and the mean age of the patient at the time of operation was 56.4 years. Preoperative diagnosis was developmental dysplasia of the hip in 94 hips, osteonecrosis in 6 hips and rheumatoid arthritis in 2 hips. The mean follow-up period was 43 months (24 to 74). Clinically, the mean Harris Hip Score was 48 points preoperatively, which improved to 92 points at the latest follow-up. Thigh pain was present in two hips (2%) at the latest follow-up although in six hips (6%) in the study group at one-year follow-up. Radiographically, according to Engh’s criteria, spot welds associated with osseointegration were observed around the inferior border of the proximal coating in all hips. We have observed no loosening or failure of the stems at the latest follow-up. Our results indicate that the new model of proximal fitting cementless fem