Which muscles are the chief invertors of the foot?

• A. Tibialis anterior and tibialis posterior
• B. Gastrocnemius and soleus
• C. Fibularis longus and fibularis brevis
• D. Flexor digitorum longus and flexor hallucis longus

Answer: (A)

Inversion of the foot is produced by muscles that pull the sole medially, and the main players are the tibialis anterior and tibialis posterior. The tibialis anterior runs from the tibia to the medial aspect of the foot (medial cuneiform and base of the first metatarsal); when it contracts, it dorsiflexes and inverts the foot, bringing the sole toward the midline. The tibialis posterior originates on the posterior surfaces of the tibia and fibula and inserts mainly on the navicular and the medial cuneiform, with extensions to other tarsals; it provides plantarflexion and inversion, crucial for maintaining the medial arch and controlling subtalar rotation. Together, they supply most of the inversion torque across common ankle positions.

The other muscles have different primary roles: gastrocnemius and soleus are mainly plantarflexors of the ankle; fibularis (peroneal) longus and brevis are primary everters, helping tilt the sole outward; flexor digitorum longus and flexor hallucis longus mainly flex the toes and contribute little to inversion. Hence, the chief invertors are the tibialis anterior and tibialis posterior.