Natural progress of a bone scan after cementless hydroxyapatite-coated total hip arthroplasty

To establish the natural progress pattern of postoperative bone uptake, a periprosthetic quantitative technetium-99m methylene diphosphonate scintiscan was done on 80 asymptomatic hips (62 patients) with uncomplicated cementless hydroxyapatite-coated total hip arthroplasties and 20 healthy control hips (10 subjects) without previous surgery. The patients were studied in eight groups at scheduled intervals of 1 to 48 months. There were 10 hips in each group. The measurement of bone uptake in the healthy untreated control group indicated that the uptake ratio in the proximal femur was physiologically higher in the metaphyseal area than in the diaphyseal area and the uptake ratio in the acetabulum appeared to be much higher than that of the proximal femur. In the patient group, the uptake ratio around the femoral stem area and the acetabular cup area showed a statistically significant decrease between 1 and 3 months after surgery and changed little after 3 months. Comparing the result of the patient group with that of the healthy untreated control group, the uptake ratio decreased much faster in the hydroxyapatite-coated metaphyseal zone than in the noncoated diaphyseal zone of the femoral stem area. In the acetabular cup area, the uptake ratio decreased fast, as in the hydroxyapatite-coated metaphyseal zone of the femoral stem area. Based on these clinical results, a quantitative bone scan may be a helpful diagnostic procedure for evaluating postoperative progress when used in conjunction with clinical symptoms and radiologic examinations.