Tibialis anterior muscle function in ankle-foot deformities as derived from intraoperative force measurements

Ankle-foot deformities, such as clubfoot, pose treatment challenges due to complex and patient-specific biomechanics. Accurate assessment of muscle force behavior is essential for tailoring interventions, yet conventional gait analysis is limited in isolating muscle-specific function. Intraoperative force measurements via the muscle's tendon offer a unique opportunity to directly quantify muscle mechanics. This study aimed to characterize the passive and active force-angle relationship of the tibialis anterior (TA) muscle, intraoperatively. Ten patients (ages 3-62) undergoing corrective foot surgery were enrolled, including five with idiopathic deformities and five with neurogenic conditions (hereditary motor and sensory neuropathy, n = 3; cerebral palsy, n = 2). Isometric TA forces were recorded at multiple ankle angles. Patients with neurogenic deformities exhibited greater ankle range of motion compared to those with idiopathic deformities (by 30.1%, p = 0.006). Passive forces were near 0 N in dorsiflexion and increased toward plantar flexion (PF), with a maximum of 50.3 N at 55° PF; no significant group differences were observed (p = 0.42). Active force-ankle angle profiles showed high inter-individual variability, with peak values ranging from 31.1 N to 431.6 N and no significant differences between groups (p = 0.81). Substantial variability in curve shape remained after normalization, indicating distinct functional profiles across patients. This study demonstrates the feasibility of directly quantifying the patient-specific force-generating capacity of the TA muscle. From a forward-looking perspective, incorporating such patient-specific force data into musculoskeletal models may improve force estimations and support more personalized surgical strategies for ankle-foot deformities.