When performing a lumbar puncture, the spinal needle is inserted in the L3-L4 or L4-L5 interspace. The surface landmark for the L4 spinous process is:
- A Intercristal (Tuffier's) line connecting the highest points of the iliac crests ✓
- B Line connecting the posterior superior iliac spines
- C Level of the 12th rib
- D Level of the umbilicus
Correct answer: A. Intercristal (Tuffier's) line connecting the highest points of the iliac crests
Explanation
Tuffier's (intercristal) line connects the highest points of both iliac crests and crosses the spine at approximately the L4 spinous process (or the L4-L5 interspace). This landmark guides needle placement below the conus medullaris (which ends at L1-L2 in adults) to safely sample CSF. The line connecting the posterior superior iliac spines (PSIS) corresponds to S2, which is too low for standard LP. The 12th rib corresponds to T12-L1. The umbilicus is at approximately L3-L4, making it a reasonable secondary landmark but less precise.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.