The Association Between Lower-Limb Muscle Mass Asymmetry and Hip Fracture Laterality in Elderly Women: A Retrospective, Dual-Energy X-ray Absorptiometry (DXA)-Based Study.

Background and objective While sarcopenia is a recognized risk factor for hip fracture, the role of side-to-side lower-limb muscle mass asymmetry in determining fracture laterality remains unclear. This study aimed to investigate whether dual-energy X-ray absorptiometry (DXA)-derived lower-limb muscle mass asymmetry is associated with hip fracture laterality in elderly women. Methods We retrospectively analyzed a cohort of 147 women aged ≥65 years with unilateral hip fractures who underwent DXA. Patients were categorized according to fracture side: left (n = 71) or right (n = 76). Lean mass (L), lean mass plus bone mineral content (LB), fat mass, and muscle indices, including the appendicular skeletal muscle index (ASMI) and skeletal muscle index (SMI), were compared between groups. Inter-limb asymmetry was assessed using left-right differences in lower-limb DXA-derived parameters. Results The left-fracture group demonstrated significantly higher left-leg lean mass plus bone mineral content compared with the right-fracture group (4928.0 ± 1223.3 g vs. 4539.8 ± 873.8 g, p = 0.030). Analysis of inter-limb differences revealed a significant association between fracture laterality and lower-limb lean mass plus bone mineral content asymmetry (p = 0.004). Overall, 62.6% (92/147) of fractures occurred on the side with greater lower-limb lean mass plus bone mineral content. Conclusions In elderly women, hip fractures are more likely to occur on the side with relatively greater lower-limb lean mass plus bone mineral content. These findings suggest that inter-limb muscle mass asymmetry, rather than absolute muscle deficiency alone, may contribute to hip fracture risk, potentially through asymmetric load transmission during falls.