Which myotome is responsible for ankle eversion?

• A. S1
• B. L5
• C. L3
• D. S2

Answer: (A)

The myotome responsible for ankle eversion is S1. This delineation is based on the specific nerve root levels that innervate the muscles involved in this action. Ankle eversion is primarily controlled by the peroneal muscles, which are mainly supplied by the superficial peroneal nerve—a branch of the common peroneal nerve that arises from the S1 nerve root.

The S1 myotome specifically contributes to the movement of eversion due to its control over the muscles that facilitate this action, including the fibularis longus and fibularis brevis. These muscles enable the foot to turn outward away from the midline of the body.

In contrast, other myotomes listed do not primarily govern ankle eversion. L5 is associated with dorsiflexion at the ankle and toe extension, while L3 is related to knee extension and hip flexion. S2 is more linked to functions such as plantar flexion and toe movements rather than eversion. Therefore, understanding the specific actions of each myotome clarifies why S1 is the correct answer for the eversion of the ankle.