The nucleus pulposus is a remnant of which embryological structure, and at which intervertebral disc level does it most commonly herniate posterolaterally?

• A Neural tube; most commonly at C5–C6 and C6–C7 levels
• B Paraxial mesoderm; most commonly at T10–T11 and T12–L1 levels
• C Endoderm; most commonly at L1–L2 level
• D Notochord; most commonly at L4–L5 and L5–S1 levels ✓

Explanation

The nucleus pulposus is the remnant of the notochord, which induces the surrounding sclerotome to form vertebral bodies. It retains high water content and viscoelastic properties. The posterior longitudinal ligament is weakest posterolaterally, making this the direction of herniation. L4-L5 disc herniation typically compresses the L5 nerve root (dorsiflexion weakness, sensory loss over dorsum of foot); L5-S1 herniation compresses S1 (plantar flexion weakness, reduced ankle jerk, sensory loss over lateral foot). These two levels account for >90% of lumbar disc herniations.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.