In an adult, the spinal cord typically terminates at which vertebral level, and lumbar puncture for spinal anaesthesia should therefore be performed no higher than which interspace?

• A T12-L1; puncture below T12
• B L1 (lower border); puncture at L2-L3 or lower ✓
• C L3-L4; puncture at L4-L5 or lower
• D S1; any lumbar interspace is safe

Explanation

In adults the conus medullaris ends at the lower border of L1, although it may extend to L2 in some individuals, so dural puncture is performed at L2-L3 or below to avoid direct cord injury. In neonates and infants the cord ends at approximately L3, requiring even lower interspaces. The L3-L4 and L4-L5 interspaces, identified by the intercristal line through the highest points of the iliac crests, are standard sites. Puncturing higher risks catastrophic conus injury with permanent lower limb deficits.

Reference: Gray's Anatomy, 42nd ed.

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Written and medically reviewed by the StethoPrep medical team.