Which muscle assists in foot inversion along with tibialis posterior?

• A. Tibialis anterior
• B. Fibularis tertius
• C. Fibularis longus
• D. Fibularis longus and fibularis brevis

Answer: (C)

Inversion of the foot is done mainly by muscles on the medial side that pull the sole inward. The tibialis posterior is a primary inverter, and another muscle that assists in inverting the foot is the tibialis anterior, especially as the foot moves into dorsiflexion during gait. The fibularis (peroneal) muscles—longus, brevis, and tertius—evade the foot (evert it) rather than invert it, so they don’t fit as partners in inversion with tibialis posterior. Therefore, tibialis anterior is the correct counterpart to assist in inversion.