Coupled Neuromusculoskeletal Finite Element Simulation Reveals Biomechanical Adaptation and Joint Tissue Risk of Ankle Exoskeleton Intervention after Stroke

Stroke-induced lower limb motor dysfunction leads to abnormal gait and severely compromises quality of life. While exoskeletons are effective rehabilitation devices, their long-term biomechanical responses and tissue-level risks remain unclear. This study employed a synergy-informed neuromusculoskeletal simulation coupled with personalized finite element (FE) analysis to quantify the biomechanical adaptations and tissue-level effects of ankle exoskeleton intervention for stroke patients. Eight male patients with chronic stroke were recruited for a 2-week exoskeleton intervention. Biomechanical data were collected before and after intervention under different exoskeleton-assisted walking conditions. The most accurate synergy-informed neuromusculoskeletal model (correlation coefficient 0.759, and root mean square error 0.164 Nm/kg for the ankle) revealed that exoskeleton-assisted walking induces compensatory biomechanical adaptations, characterized by distal assistance and proximal compensation, manifested as increased knee extension moments on the affected side and higher joint and muscle forces on the unaffected side. FE analysis showed increased ankle contact pressures, medial force transmission, lateral collateral ligament forces, and forefoot stresses after intervention. These findings suggest potential long-term risk for tissue degeneration. Current ankle exoskeletons should still be cautiously regarded as rehabilitation interventions rather than long-term assistive devices. Exoskeleton rehabilitation protocols should integrate individualized ankle and foot assessments, and exoskeleton design optimization should prioritize lightweight structures and pressure-sensitive control to enhance rehabilitation efficacy while minimizing potential long-term risk.