In lumbar disc herniation, the posterolateral disc protrusion at the L4-L5 level typically compresses which nerve root within the lateral recess?

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

Explanation

In the lumbar spine, each nerve root exits below its corresponding vertebra but traverses the intervertebral foramen above the disc at the level below. A posterolateral disc herniation at L4-L5 compresses the L5 nerve root (which is traversing the lateral recess before exiting below L5). The L4 nerve root has already exited at the L4-L5 foramen and is not affected by this disc. L4-L5 disc prolapse: L5 root compression → weakness of dorsiflexion (tibialis anterior, extensor hallucis longus), sensory loss on dorsum of foot and big toe. L5-S1 disc prolapse: S1 root → calf, Achilles reflex.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.