Multi-Scale Mapping of Diaphyseal Stresses Across Gait Modalities Using Femoral Digital Twins

Abstract

Bone health decreases with age and can culminate in fractures with particularly devastating consequences in the femur. Exercise-induced mechanical loading can be prescribed as preventative care, but clinical recommendations are hindered by a lack of clarity regarding the mechanical strains experienced during habitual locomotive tasks such as walking, stair descent, and stair ascent. We used subject-specific, muscle-driven finite element digital twins of post-menopausal women to conduct a multi-scale analysis of the spatiotemporal distribution of femoral principal strains during each task. At the macroscopic level, strains peaked during both the early and late stance phases of the gait cycle and the femur was subjected to a combination of bending and torsional loads for all tasks. Mesoscale analyses revealed a noticeable regional partition: strain distributions were highly consistent across tasks and timepoints in the proximal and mid-diaphysis, but deviated in the distal diaphysis. At the tissue level, peak strains during stair ascent were lower in the proximal region but higher in the distal region compared to walking and stair descent; meanwhile, in the mid-diaphysis, peak strains during stair descent exceeded those during walking. Together, these findings indicate that while the global femoral loading environments were similar across tasks, there was heterogeneity in the spatial and temporal mechanical response. Incorporating stair activity into daily routines can diversify bone remodeling stimulation throughout the diaphysis.