Evertors

Evertors are muscles that produce eversion, the outward turning or rotating of a body part. In human anatomy, the term most commonly refers to the muscles that evert the foot at the subtalar joint, located in the lateral compartment of the leg.

The primary evertors of the foot are the fibularis (peroneus) longus, fibularis brevis, and fibularis tertius. The fibularis longus originates from the head and upper shaft of the fibula and inserts on the base of the first metatarsal and the medial cunningham (medial cuneiform). The fibularis brevis originates from the distal two-thirds of the fibula and inserts on the tuberosity of the fifth metatarsal. The fibularis tertius arises from the distal fibula and inserts on the dorsal base of the fifth metatarsal. Together, these muscles primarily evert the foot and can assist in plantarflexion or dorsiflexion depending on the foot’s position.

Innervation follows the two branches of the common fibular nerve: the superficial fibular nerve supplies the fibularis longus and brevis, while the fibularis tertius is supplied by the deep fibular nerve. The extensor digitorum longus can also assist in eversion, particularly when the foot is dorsiflexed, but its primary actions are dorsiflexion and toe extension.

Function and clinical relevance: Evertors help stabilize the ankle by opposing inversion. Weakness or injury to the peroneal muscles or the superficial fibular nerve can contribute to lateral instability and a predisposition to ankle sprains, while overuse can lead to peroneal tendonitis. Understanding evertors aids in assessment of ankle mechanics and rehabilitation.