Monitoring skeletal response to treatment: Which site to measure in the femur?

In the past it was usual to interpret bone mineral density (BMD) scans of t he femur using the femoral neck, trochanter; or Ward's triangle sites. Rece ntly, a report by the International Committee for Standards in Bone Measure ment recommended that the total hip should be the preferred site for the in terpretation of femur BMD, and another study described a new central hip si te that may offer improved precision. This article compares the longitudina l sensitivities of the different femur BMD sites for monitoring patient res ponse to treatment. The study population was 152 postmenopausal women enrol led in a trial of a bisphosphonate therapy. Spine and hip BMD scans were pe rformed at 0, 1, and 2 yr. The mean percentage change at 2 yr was calculate d for six sites ill the hip, and the spine was also included for comparison . Treatment effect was defined as the difference in the BMD change between the treated and placebo groups. Although the data analysis incorporated a t erm fur a calibration change caused by a repair of the dual X-ray absorptio metry scanner, the effect of this event on the estimation of treatment effe ct was negligible. Longitudinal sensitivity was derived by dividing the tre atment effect by the root mean square error (RMSE) of the statistical model . Results (and standard errors) normalized to the ratio of treatment effect : RMSE for femoral neck BMD were as follows: femoral neck: 1.00; trochanter : 1.33 (0.38); intertrochanteric: 0.84 (0.41); total hip: 1.20 (0.38); Ward 's triangle: 1.03 (0.27); central hip: 1.09 (0.30); spine: 2.08 (0.45). At none of the femur sites was the change in BMD large enough to allow monitor ing of response to treatment in individual patients. However, for studies i nvolving the follow-up of a group of subjects, the longitudinal sensitiviti es of the different femur sites were equal within the statistical errors of the study. In particular, total hip BMD appears to be as effective as femo ral neck BMD for detecting response to treatment in the femur in the settin g of a clinical trial or similar research study.