A 42-year-old man has low back pain radiating down the posterolateral leg and lateral foot with weakness of great toe dorsiflexion. An axial T2-weighted MRI shows a left posterolateral disc prolapse at L4-L5. Which nerve root is compressed?

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

Explanation

C posterolateral L4-L5 disc herniation compresses the traversing L5 root, producing pain along the posterolateral leg, lateral foot sensory loss, and weak extensor hallucis longus. The L4 root exits through the L4-L5 foramen above the disc level and escapes compression here. The S1 root would be compressed by an L5-S1 prolapse, which classically causes ankle plantarflexion weakness and an absent ankle jerk.

Reference: Snell's Clinical Neuroanatomy, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.