A 45-year-old male has low back pain radiating to the right leg with numbness in the web space between the first and second toes and weakness of foot dorsiflexion (extensor hallucis longus). MRI shows L4-L5 disc prolapse compressing the right nerve root. Which nerve root is compressed?

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

Explanation

L5 nerve root compression classically produces sensory loss in the first web space of the foot (L5 dermatome) and weakness of dorsiflexion — particularly EHL (extensor hallucis longus, the most specific L5 muscle) and extensor digitorum longus. Deep peroneal nerve territory overlaps but the root level is L5. S1 compression produces sensory loss over the lateral foot and sole, weakness of plantar flexion and eversion, and a diminished ankle jerk (S1 reflex). L4 compression produces medial leg/foot numbness, weakness of knee extension/inversion, and diminished knee jerk. At L4-L5 disc level, the L5 root is typically compressed (the disc herniation exits below the pedicle of L5).

Reference: Maheshwari Essential Orthopaedics, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.