Stage-dependent muscle force patterns during femoral fracture reduction: a patient-specific modeling study.

During fracture reduction, bone segment pose changes induce complex muscle force responses, but their patterns and association with fracture geometry remain unclear. Using CT data from 16 femoral shaft fracture cases, patient-specific musculoskeletal models were developed in AnyBody. A staged fracture reduction simulation framework comprising traction, derotation, translational alignment, and length restoration was established. Muscle force distribution exhibited heterogeneity and stage-dependent characteristics. Additionally, muscle force showed a multivariate association with fracture geometric parameters. The multivariate model achieved an R2 of 0.551, outperforming the univariate model. These findings provide quantitative biomechanical evidence for understanding muscle responses during fracture reduction.