A 45-year-old man presents with back pain and progressive weakness of knee extension and loss of knee jerk. MRI shows a posterolateral disc prolapse at L3-L4 level. Which nerve root is most likely compressed?

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

Explanation

In posterolateral disc prolapse, the herniated disc compresses the nerve root that exits below the disc level through the same intervertebral foramen. At L3-L4, the L4 nerve root is compressed (not L3, which has already exited above). L4 nerve root compression causes: weakness of knee extension (quadriceps) and hip adductors, diminished or absent knee jerk (patellar tendon reflex via L3-L4, primarily L4), and sensory loss over the medial leg and medial aspect of the dorsum of the foot. L5 root compression causes extensor hallucis longus weakness and dorsiflexion weakness; S1 compression causes ankle jerk loss.

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

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Written and medically reviewed by the StethoPrep medical team.