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Epidural Anatomy — FRCA Final MCQ

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EasyRegional AnaesthesiaEpidural AnatomyFRCA Final

Which sequence correctly describes the principal structures traversed during a midline lumbar epidural insertion, from the skin to entry into the epidural space?

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Correct answer: C — Skin → subcutaneous fat → supraspinous ligament → interspinous ligament → ligamentum flavum

In a midline lumbar approach, the needle passes through the skin and subcutaneous tissue, then traverses the supraspinous ligament at the tips of the spinous processes, the interspinous ligament between adjacent processes, and finally the ligamentum flavum before entering the posterior epidural space. Therefore, C is correct. B reverses the supraspinous and interspinous ligaments, while D incorrectly places the ligamentum flavum superficial to the interspinous ligament. C also places the ligamentum flavum too superficially. The posterior longitudinal ligament in C and E lies at the anterior aspect of the vertebral canal and contributes to the anterior boundary of the epidural space; it is not traversed during a standard posterior midline epidural insertion.

Reference: Macpherson D, Quondamatteo F, Broom M. Update on applied epidural anatomy. Figure 4. BJA Education. 2022;22(5):182–189. https://pubmed.ncbi.nlm.nih.gov/34686581/