Single-site vs multisite bone density measurement for fracture prediction

Background: Bone density measurement with dual-energy x-ray absorptiometry is widely used for fracture risk assessment. Discordance between measurement sites is common, but it is unclear how this affects fracture prediction. Methods: We performed a historical cohort study among 16 505 women 50 years or older at the time of baseline dual-energy x-ray absorptiometry of the spine and hip (mean +/- SD observation period, 3.2 +/- 1.5 years). The study population was drawn from a database that contains all clinical dual-energy x-ray absorptiometry test results for the province of Manitoba, Canada. Each subject's longitudinal health service record was assessed for the presence of fracture codes after bone density testing. The likelihood ratio test was used to assess the improvement in fracture prediction from Cox proportional hazards models using bone density covariates from a single site or from combined sites. Results: Age-adjusted hazard ratios (HRs) per standard deviation for osteoporotic fracture ranged from 1.61 (95% confidence interval [CI], 1.39-1.87) for the lumbar spine to 1.85 (95% CI, 1.70-2.01) for the total hip, with intermediate values for the femur neck (HR, 1.76 [ 95% CI, 1.62-1.92]) and trochanter ( HR, 1.77 [95% CI, 1.63-1.92]). For fracture prediction, use of the minimum bone density measurement was no better than use of a hip measurement alone. When the total hip measurement was included in a fracture prediction model for the overall population, none of the other measurements added substantial information. The spine was the most useful site for the prediction of spine fractures alone. Conclusions: Proximal femur bone density measurements consistently outperformed lumbar spine measurements for global fracture prediction. In this cohort, the total hip was the best site for overall fracture assessment.