In L5 radiculopathy, which muscle demonstrates motor weakness?

• A. Extensor hallucis longus
• B. Tibialis anterior
• C. Peroneus longus
• D. Quadratus femoris

Answer: (A)

L5 radiculopathy most affects muscles that dorsiflex the foot and extend the big toe, because the L5 nerve root supplies these motor functions. The extensor hallucis longus is a key toe-extensor muscle mainly innervated by the L5 nerve root, so weakness here is a classic and specific sign of L5 involvement. When you test this muscle, difficulty extending the great toe points to L5 radiculopathy.

Tibialis anterior also helps with dorsiflexion, but it has a stronger L4 contribution, so its weakness is less specific to L5. The peroneus longus mainly handles eversion and plantarflexion, not dorsiflexion of the toe, making it a less reliable indicator of L5 injury. Quadratus femoris is innervated by a nerve root combo including L5-S1 and is not a primary dorsiflexor, so its weakness wouldn’t uniquely indicate L5 radiculopathy.