A 40-year-old man presents with low back pain radiating down the posterolateral aspect of the left leg to the dorsum of the foot and great toe, with numbness and weakness of great toe dorsiflexion. Straight leg raise is positive at 40° on the left. The nerve root most likely affected is:

• A L5 nerve root ✓
• B L3 nerve root
• C L4 nerve root
• D S1 nerve root

Explanation

L5 radiculopathy presents with pain and paraesthesia in the posterolateral thigh, lateral leg, and dorsum of the foot to the great toe (L5 dermatome). The hallmark motor deficit is weakness of great toe and foot dorsiflexion (extensor hallucis longus is primarily L5). The ankle jerk (S1) is preserved. L4 radiculopathy causes quadriceps weakness and reduced knee jerk; S1 causes weakness of plantar flexion and reduced ankle jerk. The L4–L5 disc level is most commonly involved.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.