When performing a lumbar puncture in an adult, the needle is inserted between which vertebral levels to safely enter the subarachnoid space without risk of spinal cord injury?
- A L3–L4 or L4–L5 interspaces ✓
- B L1–L2 interspace
- C T12–L1 interspace
- D L5–S1 interspace only
Correct answer: A. L3–L4 or L4–L5 interspaces
Explanation
The adult spinal cord ends at the L1–L2 level (conus medullaris); below this, only the cauda equina nerve roots are present, which float freely in CSF and are pushed aside rather than damaged by a needle. L3–L4 or L4–L5 is therefore the standard site for lumbar puncture. The L4–L5 space is identified by the Tuffier's (intercristal) line drawn between the iliac crests, which crosses the L4 spinous process. Insertion at L1–L2 or above risks spinal cord injury.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.