Which is an expected sacral S1-S2 muscle function?

• A. Ankle eversion
• B. Hip adduction
• C. Knee flexion
• D. Ankle dorsiflexion

Answer: (A)

Sacral S1-S2 motor function includes muscles that move the ankle and foot through the lower leg nerves. Ankle eversion is performed by the fibularis (peroneus) longus and brevis muscles. These muscles are innervated by the superficial fibular nerve, which carries motor fibers that include contributions from the sacral levels, particularly S1-S2. That makes ankle eversion a function tied to S1-S2.

In contrast, hip adduction is mainly controlled by the obturator nerve (L2–L4), knee flexion is driven primarily by the hamstrings via the sciatic nerve (L5–S2, with some overlap), and ankle dorsiflexion is mainly performed by muscles innervated by the deep peroneal nerve (L4–L5). So ankle eversion best fits the sacral S1-S2 motor profile.