To observe the progress pattern of quantitative bone uptake in asymptomatic patients with uncomplicated cementless total hip arthroplasties.

A periprosthetic quantitative 99mTc-MDP scintiscan was performed in 62 asymptomatic patients (80 hips) and 10 unoperated normal control group (20 hips) . The patients were studied in eight groups (10 hips each time) at scheduled time intervals (1, 3, 6, 9, 12, 24, 36, and 48 months) . We calculated the comparative ratio of uptake in each of the periprosthetic zones to both sacroiliac joints and compared these results with the control group.

The uptake ratio of all the periprosthetic areas (cup and stem areas) peaked at one month after the operations (p<0.05) , and a statistically significant decrease was shown between one and three months (p<0.05) . After three months, the activity was relatively uniform and stable. Bone uptake on the proximal femur in the normal unoperated control group indicated that bone uptake in the metaphyseal area was physiologically high (p<0.01) . Comparing this result with that of the patient group, bone uptake decreased much faster in the HA-coated metaphyseal area than in the non-coated diaphyseal area.

Previous studies of bone scan after cementless hip arthroplasties reported that bone uptake in the HA-coated metaphyseal area was higher and had longer stabilizing time than that in the non-coated diaphyseal area. And they claimed that evaluation of bone uptake was meaningless in the acetabular cup area. However, our measurement of bone uptake on the proximal femur in the normal unoperated control group indicated that bone uptake in the metaphyseal area was physiologically high. Comparing this result with that of the patient group, bone uptake decreased much faster in the HA-coated metaphyseal area than in the non-coated diaphyseal area. And when a quantitative bone scan of the acetabular cup area was performed and compared to normal acetabulum in the control group, we found that, unlike the claims of several previous studies, the bone scan does produce meaningful results.