Which is an expected sacral S1-S2 muscle function?

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 nerve roots contribute to muscles that move the ankle and foot, so the action most consistently linked to these roots is ankle eversion. The fibularis (peroneal) muscles, which evert the foot, are innervated by nerves carrying sacral input (including S1). In contrast, ankle dorsiflexion is mainly from L4-L5 via the deep fibular nerve, knee flexion from the hamstrings (primarily L5-S2), and hip adduction from the obturator nerve (L2-L4). Thus, ankle eversion best aligns with sacral S1-S2 muscle function.

Sacral S1-S2 nerve roots contribute to muscles that move the ankle and foot, so the action most consistently linked to these roots is ankle eversion. The fibularis (peroneal) muscles, which evert the foot, are innervated by nerves carrying sacral input (including S1). In contrast, ankle dorsiflexion is mainly from L4-L5 via the deep fibular nerve, knee flexion from the hamstrings (primarily L5-S2), and hip adduction from the obturator nerve (L2-L4). Thus, ankle eversion best aligns with sacral S1-S2 muscle function.