Which muscle is a prime mover for ankle inversion?

Which muscle is a prime mover for ankle inversion?

• A. Tibialis anterior
• B. Flexor digitorum longus
• C. Peroneus tertius
• D. Tibialis posterior

Answer: (D)

Inversion of the ankle is produced most powerfully by the tibialis posterior. Its tendon crosses behind the medial malleolus and attaches to the navicular and medial cuneiform, allowing it to pull the sole of the foot medially at the subtalar joint and help support the foot’s arch. This makes tibialis posterior the prime mover for ankle inversion during resisted ROM tests. Other muscles can assist or contribute to other actions: tibialis anterior inverts the foot but is mainly a dorsiflexor; flexor digitorum longus assists with inversion but its primary roles are toe flexion and plantarflexion; peroneus tertius everts the foot and assists with dorsiflexion, not inversion.

Inversion of the ankle is produced most powerfully by the tibialis posterior. Its tendon crosses behind the medial malleolus and attaches to the navicular and medial cuneiform, allowing it to pull the sole of the foot medially at the subtalar joint and help support the foot’s arch. This makes tibialis posterior the prime mover for ankle inversion during resisted ROM tests. Other muscles can assist or contribute to other actions: tibialis anterior inverts the foot but is mainly a dorsiflexor; flexor digitorum longus assists with inversion but its primary roles are toe flexion and plantarflexion; peroneus tertius everts the foot and assists with dorsiflexion, not inversion.