Question

Spinal anaesthesia is given at which level?

• A. L1-2
• B. L3-4
• C. S1
• D. Midline thoracic segments

Hint:

Inject below the conus medullaris; Tuffier's line marks the L3-L4 space.

Answer 1

The Correct Option is B

Step 1: Recall the anatomy. In adults the spinal cord ends (conus medullaris) at the lower border of L1 to L2, so the cord must not be punctured below this point during lumbar puncture.
Step 2: Choose a safe interspace. The L3-L4 (or L4-L5) interspace lies well below the conus, in the region of the cauda equina, where the needle can enter the subarachnoid space without injuring the cord.
Step 3: Use the surface landmark. Tuffier's line, joining the tops of the iliac crests, crosses the spine at the L4 vertebra or the L3-L4 interspace, marking the standard site for spinal anaesthesia.
Step 4: Exclude the others. L1-2 is too high and risks cord injury, S1 is below the usual dural sac end and is not a routine site, and midline thoracic injection is not used for spinal anaesthesia.
Conclusion: Spinal anaesthesia is given at the L3-L4 level. The printed key (B) is medically correct.