The posterior longitudinal ligament (PLL) is narrower in the lumbar region than the cervical region. Which clinical consequence follows from this anatomical feature?

• A Cervical disc herniations tend to be central; lumbar disc herniations tend to be posterolateral, compressing exiting nerve roots ✓
• B The lumbar spinal canal is narrower than the cervical canal
• C Posterior neck pain occurs because the PLL is stronger in the neck
• D The PLL narrowing has no clinical consequence; only the anterior longitudinal ligament matters

Explanation

The posterior longitudinal ligament provides a central reinforcement of the posterior annulus fibrosus; it is broad in the cervical region (covering the full disc width) but narrows in the lumbar region, creating unsupported lateral zones at the disc edges. This means lumbar disc herniations preferentially occur in the posterolateral direction (through the uncovered lateral annulus), where they compress the nerve root exiting at the next lower level. Cervical disc herniations, supported by the broad PLL centrally, are more likely to prolapse centrally, compressing the spinal cord itself. This anatomical difference explains why lumbar herniations more often cause radiculopathy whereas cervical herniations more often cause myelopathy.

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

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Written and medically reviewed by the StethoPrep medical team.