Interpreting forearm flexural rigidity from cortical bone mechanics technology under forward-fall loading: A scenario-based load-to-capacity framework.

Abstract

Fractures occur when loads exceed bone capacity. Cortical Bone Mechanics Technology (CBMT) noninvasively assesses ulnar bending and yields flexural rigidity (EI), a mechanical property strongly associated with whole-bone bending strength. No framework places CBMT-reported EI on a fall-demand scale. We developed an illustrative, reduced-order scaling framework to estimate the CBMT-reported EI required for modeled ulnar bending capacity to match bending-equivalent demand across forward-fall-on-an-outstretched-hand (FOOSH) scenarios. This central required-EI estimate was denoted EI₅₀. The model varied body size, surface compliance, upper-extremity compliance, two-hand versus one-hand loading, and effective moment arm. Across 324 primary scenarios, EI₅₀ ranged from 11.0 to 66.2 N·m². Median EI₅₀ doubled from 19.0 N·m² for symmetric two-hand FOOSH to 38.0 N·m² for unilateral single-hand FOOSH. For median-body-size older-adult women, EI₅₀ ranged from 14.1 to 22.9 N·m² for two-hand loading and 28.2-45.7 N·m² for single-hand loading; corresponding ranges for men were 16.2-26.3 and 32.4-52.6 N·m². A sensitivity analysis using a published 2.5-4.0 kN standing-fall force envelope yielded wider required-EI ranges of 25.4-50.8 N·m² for two-hand conditions and 50.8-101.6 N·m² for single-hand conditions across the prespecified moment arms. CBMT EI is a mechanically interpretable forearm cortical phenotype that can be contextualized against explicitly defined fall-demand scenarios. The framework is illustrative and does not estimate site-specific or patient-level fracture probability.