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· Ex-USMLE Forums Staff
752 Posts
Discussion Starter · #1 · (Edited)
A very high yield anatomical question, What layers does the spinal needle traverse when we do lumbar puncture?

Have a look at this illustration
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Original image from wikimedia commons

As per the numbers in the illustration
1- Skin
2- Facia and SC fat
3- Surpaspinous ligament
4- Interspinous ligament
5- Ligamentum flavum
6- Epidural space and fat (epidural anesthesia needle stops here)
7- Dura

Right after that the needle pops into the subarachnoid space where the CSF is swimming.

Important Notes:

  • 3,4, and 5 are collectively occuring in the interlaminar space.
  • There's no subdural space (as FA is saying), it's a potential space that can be filled by fluid but normally it's empty.
  • The best intervertebral space is between L3/L4 or L4/L5 usually lower levels in children.
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