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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.

· Registered
7 Posts
I was learning from HY Gross Anatomy
Lumbar puncture:
1. Skin-----------------------Spune-le
2. Superficial fascia----------Sa
3. Supraspinous ligament---Studieze
4. Interspinous ligament----In
5. Ligamentum flavum------Laborator
6. Epidural space containing the internal vertebral venous plexus -E
7. Dura mater D
8. Arachnoid A
9. Subarachnoid space containing cerebrospinal fluid.

Spune-le Sa Studieze In Lab EDA; Hope it works

· Registered
45 Posts
Clarifying The Safe Level for Lumbar Puncture and Presence of Subdural Space


I am going to comment on two points regarding Lumbar Puncture:

1- In adults, spinal cord ends at the LOWER border of L1. Thus, the level at which we can insert the needle in ADULTS could be L2-L3 or lower, i.e., as long as you avoid the first lumbar space (L1-L2), you are good. In children and infants, spinal cord ends at a lower level so going for L4-L5 is wise.

2- Regarding the presence or absence of a Subdural space; in fact this space is present but in LIVING ADULTS the pressure of CSF pushes the Arachnoid against Dura thus obliterating this space, so practically once the tip of the needle hits Dura, you have already hit arachnoid and now the needle is swimming in CSF. We have two "give" s when we do Lumbar Puncture; first "give" is when the needle pierces Ligamentum Flavum, second "give" is when the needle pierces Dura.
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