Biomechanical assessment of vertebral fracture risk incorporating the effect of paraspinal muscles.

Vertebral fractures are a major public health issue worldwide. Current assessment standards, like volumetric bone mineral density (vBMD), are limited because they overlook the critical biomechanical role of paraspinal muscles. This study directly compares quasistatic and musculoskeletal models on their performance in estimating the load-to-strength ratio (LSR) and determines their efficacy in vertebral fracture risk assessment. Our case-control study included 70 subjects (18 with vertebral fractures and 52 controls) who underwent quantitative CT for vBMD measurement and finite element analysis, which yielded biomechanical CT (BCT) to determine vertebral strength. The compressive loads on L2 vertebra under three postures (30°, 45°, and 90° flexion) were computed and LSRs were calculated. Group differences in vBMD, BCT strength, muscle density, and LSRs were compared, while their diagnostic performance was evaluated. For fracture risk assessment, LSRs demonstrated higher performance (AUC: 0.89–0.94) vs. vBMD (AUC: 0.71), and certain improvements over BCT-strength. Quasistatic and musculoskeletal models produced similar loads at 30° and 45°, while musculoskeletal model predicted markedly higher loads at 90° (+ 48.4%). Overall, incorporating paraspinal muscle-related loading into LSR improves fracture risk assessment beyond vBMD. Model choice becomes more influential under high-flexion conditions.