Bone strain index for fracture risk assessment in older men-the prospective STRAMBO study.

Objective: Bone strain index (BSI) is a noninvasive index of bone strength assessed on lumbar spine and femur dual energy X-ray absorptiometry scans using the finite-element method. In this study, we assess the link of the lumbar spine and hip BSI with fracture risk in older men.

Design: Prospective cohort study.

Methods: A cohort of 825 men aged ≥60 was followed up for 12 years. Lumbar spine and hip bone mineral density, BSI, Fracture Risk Assessment Tool (FRAX) for major osteoporotic fractures (MOPFx), and lumbar spine trabecular bone score (TBS) were assessed at baseline. Overall, 159 men had 198 incident fractures.

Results: After adjustment for FRAX and prior falls, a higher BSI was associated with a higher fracture risk, eg, trochanter BSI: (HR = 1.34 per standard deviation (SD) increase, 95% CI: 1.14-1.58, P < .001). Patterns were similar for MOPFx, vertebral, nonvertebral, and multiple fractures. The fracture risk was higher in the highest vs the lowest BSI quartiles. The associations were the strongest for the BSI of the lumbar spine and trochanter. When the TBS and BSI were analyzed jointly, their respective contributions to fracture prediction varied according to the fracture and the site of the BSI, eg, both the TBS and the trochanter BSI contributed to the MOPFx prediction (TBS: HR = 1.38/SD decrease, 95%CI: 1.04-1.84, P < .05; BSI: HR = 1.49/SD increase, 95% CI: 1.16-1.91, P < .005).

Conclusion: The BSI at both the lumbar and the femoral sites was associated with a higher fracture risk independently of FRAX and prior falls in older men followed prospectively for 12 years.