Unexpected muscle actions at the subtalar joint: implications for the study of multijoint movement

A cadaver model was used to investigate the actions of muscles crossing the subtalar joint. Subtalar joint moment arms of tibialis anterior were evaluated using measured tendon excursions, and the effective attachment site of the Achilles tendon on the calcaneus was located using measurements made using a six degree-of-freedom load cell. Tibialis anterior was found to be a weak inverter, with mean subtalar joint moment arms of 0.6±0.3 cm, and the attachment site of the Achilles tendon was found to shift substantially in the mediolateral direction with subtalar joint rotation. These observations contrasted with standard anatomical descriptions and model representations of these structures.