During spinal anesthesia, the spinal needle passes through several structures to reach the subarachnoid space where the anesthetic is injected.
Structures pierce from outside to inside during spinal anesthesia and lumbar puncture-
1. Skin (outermost layer)
2. Subcutaneous tissue
3. Supraspinous ligament: A strong fibrous band running along the tips of the spinous processes of the vertebrae.
4. Interspinous ligament: Connects adjacent spinous processes.
5. Ligamentum flavum: It is often described as the toughest layer to penetrate.
6. Epidural space (space just outside the dura mater)
7. Dura mater
8. Arachnoid mater (last structure to be pierced during spinal anesthesia and lumbar puncture)
9. Subarachnoid space: Contains cerebrospinal fluid (CSF), where the anesthetic is deposited to achieve spinal anesthesia.
Important point-
• During epidural anesthesia, the needle passes through the supraspinous ligament, interspinous ligament, and ligamentum flavum, but it does not pierce the dura mater.
• In contrast, during spinal anesthesia, the needle advances further to penetrate the dura mater and enter the subarachnoid space, where the anesthetic is directly administered into the cerebrospinal fluid.