We followed 66 total hip arthroplasties using a cement-less Omniflex femoral component with different surface morphology in 51 patients for a mean of 98 months (72 to 138). There were 57 women and nine men, and the mean age of the patient at the time of operation was 55.4 years (39 to 70). Preoperative diagnosis was osteoarthritis secondary to congenital hip dislocation and dysplasia in 64 hips, rheumatoid arthritis in two hips. This series was divided into three groups according to the extent of surface treatment in the proximal part of the femoral component. A circumferential Hydroxyapatite or titanium plasma-spray coated Omniflex stem was used in 33 hips (Group A). A patchy titanium-beads coated stem and a smooth surfaced stem of the same design were used in 25 hips (Group B) and eight hips (Group C), respectively.

Clinically, the mean Harris Hip Score was 54 points preoperatively, which improved to 89 points at the latest follow-up. Incidence of thigh pain was the lowest in Group A ( 6%) in comparison with in Group B (28%) and Group C (25%). Radiographically, the aseptic loosening rate of the femoral component was none in Group A, 16% in Group B and 75% in Group C. Incidence of femoral osteolysis was almost the same rate among the three groups; 38% in Group A, 40% in Group B, and 50% in Group C. However only in Group A, no Osteolysis was found distal to the lesser trochanter level. The femoral revision was performed in two hips of Group C. This study elucidated that the extent of surface treatment would be one of the important factors to influence the stem stability and the occurence of femoral osteolysis.

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