Bone-muscle indices as risk factors for fractures in men: the Osteoporotic Fractures in Men (MrOS) Study

Objective: To assess bone-muscle (B-M) indices as risk factors for incident fractures in men. Methods: Participants of the Osteoporotic Fractures in Men (MrOS) Study completed a peripheral quantitative computed tomography scan at 66% of their tibial length. Bone macrostructure, estimates of bone strength, and muscle area were computed. Areal bone mineral density (aBMD) and body composition were assessed with dual-energy X-ray absorptiometry. Four year incident non-spine and clinical vertebral fractures were ascertained. B-M indices were expressed as bone-to-muscle ratios for: strength, mass and area. Discriminative power and hazards ratios (HR) for fractures were reported. Results: In 1163 men (age: 77.2 +/- 5.2 years, body mass index (BMI): 28.0 +/- 4.0 kg/m(2), 4.1 +/- 0.9 follow-up years, 7.7% of men >= 1 fracture), B-M indices were smaller in fractured men except for bending and areal indices. Smaller B-M indices were associated with increased fracture risk (HR: 1.30 to 1.74) independent of age and BMI. Strength and mass indices remained significant after accounting for lumbar spine but not total hip aBMD. However, aBMD correlated significantly with B-M indices. Conclusion: Mass and bending B-M indices are risk factors for fractures in men, but may not improve fracture risk prediction beyond that provided by total hip aBMD.