A spinal needle is being inserted at L4–L5 in the midline. Correct order of ligaments pierced from superficial to deep is:

• A Interspinous → supraspinous → posterior longitudinal ligament → dura mater
• B Supraspinous → interspinous → posterior longitudinal ligament → dura mater
• C Ligamentum flavum → interspinous → supraspinous → dura mater
• D Supraspinous → interspinous → ligamentum flavum → dura mater ✓

Explanation

In the midline approach, the spinal needle traverses, in order: skin → subcutaneous fat → supraspinous ligament → interspinous ligament → ligamentum flavum (which gives a characteristic 'pop' or 'give') → epidural space → dura mater → subdural space → arachnoid mater → subarachnoid space. The posterior longitudinal ligament lies on the anterior surface of the spinal canal and is not traversed during spinal anaesthesia. The characteristic resistance-to-loss encountered at the ligamentum flavum is used in epidural techniques.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.