When performing a lumbar puncture at the L3–L4 interspace, which clinical landmark is used to identify this level?
- A A horizontal line connecting the iliac crests (Tuffier's line / intercristal line) ✓
- B A line connecting the posterior superior iliac spines (PSIS)
- C The spinous process of L1 identified below the 12th rib
- D The sacral dimple of Venus marking the S2 level
Correct answer: A. A horizontal line connecting the iliac crests (Tuffier's line / intercristal line)
Explanation
Tuffier's line (intercristal line) connects the highest points of the iliac crests and passes through the L4 spinous process (or the L3–L4 interspace) in most adults. This is the primary surface landmark for lumbar puncture, ensuring the needle is inserted below the conus medullaris (which ends at L1–L2 in adults), minimizing risk of spinal cord injury. In obese patients, the intercristal line may correspond to L4–L5 instead. A line through the PSIS corresponds to S2 (posterior dural sac end and dural sac termination point).
Reference: BD Chaurasia's Human Anatomy, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.