Transfemoral bone-anchored limb use changes dynamic hip muscle forces during walking

People with unilateral transfemoral amputation commonly experience pain at the residual limb-socket interface and heightened risk of musculoskeletal overuse injuries. Compensatory movement patterns acutely alleviate pain but can contribute to chronic aberrant muscle function and joint loading. Bone-anchored limbs have been shown to normalize joint loading during walking compared to socket prostheses, but their effects on muscle forces are not well understood. In this study, we compared dynamic hip muscle forces in all three planes of motion during walking before and after transfemoral bone-anchored limb implantation. Overground walking motion capture data were collected from 19 participants before (in socket prosthesis) and 12 months following bone-anchored limb implantation. Bilateral hip muscle forces were estimated during stance using subject-specific musculoskeletal models, resolved into anteroposterior, mediolateral, and superoinferior components, and compared across timepoints. After bone-anchored limb implantation, amputated-side hip abductor muscle forces were increased throughout stance (p ≤ 0.048), suggesting greater force-generating capacity of hip-spanning muscles during walking. Amputated-side hip flexor posterior muscle forces were decreased following implantation during terminal stance (p < 0.001), which may contribute to reduced anterior hip joint loading in pre-swing observed in bone-anchored limb users. Hip abductor muscle forces were more symmetric during single limb support (p < 0.034) and flexor muscle forces were more asymmetric during terminal stance (p = 0.047) following bone-anchored limb implantation. This study provides new insights of how bone-anchored limbs influence hip muscle function during walking, with implications for hip osteoarthritis development and progression in this population.