For a lumbar puncture, the needle is inserted in the midline at the L3–L4 or L4–L5 interspinous space. The surface landmark used to identify the L4 spinous process is:

• A The line connecting the posterior superior iliac spines (PSIS), corresponding to S2
• B The level of the umbilicus, corresponding to L1
• C Tuffier's line (intercristal line) connecting the highest points of both iliac crests ✓
• D The line connecting the iliac tubercles (interspinous line), corresponding to L5

Explanation

Tuffier's (intercristal) line, drawn between the highest points of the iliac crests, crosses the spine at the L4 spinous process (or the L4–L5 interspace). This landmark is used to safely perform lumbar puncture below the termination of the spinal cord (conus medullaris at L1–L2 in adults), avoiding cord injury. The PSIS line corresponds to S2 (sacral hiatus landmarks). The umbilicus corresponds to L1 in most adults. The iliac tubercle line is at L5.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.