To perform a Lumbar puncture, the insertion is commonly made at:

DSSSB 13 August 2024

Medical & Surgical Nursing

Easy

Appeared in: DSSSB 13 August 2024

Explanation

The L3-L4 interspace is a standard and safe site for performing a lumbar puncture.
This location is chosen because the spinal cord in adults typically ends at the L1-L2 vertebral level (an area called the conus medullaris).
Inserting the needle below the L2 vertebra ensures entry into the subarachnoid space without risking direct injury to the solid spinal cord.
At the L3-L4 level, the spinal canal contains the cauda equina, a bundle of nerve roots that float in the cerebrospinal fluid (CSF) and can move away from the advancing needle, minimizing the risk of neurological damage.

Option B: This site is in the upper thoracic spine. The spinal cord is present at this level, and inserting a needle here carries an extremely high risk of causing direct, severe, and permanent spinal cord injury.
Option C: Similar to T1-T2, this site is in the thoracic region where the spinal cord is located. A puncture at this level is contraindicated as it could lead to catastrophic spinal cord damage.
Option D: This refers to the sacral vertebrae. In adults, the sacral vertebrae (S1-S5) are fused into a single bone (the sacrum). There is no intervertebral space between S1 and S2 to allow for needle insertion.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Anatomical landmarks and the safe insertion site for a lumbar puncture procedure as background academic context rather than a clinical decision trigger.
Correct landmarking is a critical nursing and medical skill to ensure patient safety during a lumbar puncture. The primary landmark is Tuffier's line (an imaginary line connecting the top of the iliac crests), which helps identify the L4 spinous process or L4-L5 interspace.
A key nursing role during the procedure is to help the patient maintain a flexed position (either lateral decubitus or sitting) to open up the interspinous spaces, making needle insertion easier and safer.
What if? If the patient is a neonate or young infant, the spinal cord terminates at a lower level, around the L3 vertebra. To maintain a safe margin, the puncture site is chosen even lower, typically at the L4-L5 or L5-S1 interspace.

How to Approach the Question

This is a factual recall question based on anatomical knowledge.
First, identify the core procedure mentioned in the stem: Lumbar Puncture (also known as a spinal tap).
Recall the primary safety principle of this procedure: to avoid injuring the spinal cord.
Remember the key anatomical fact: the adult spinal cord typically ends at the L1-L2 vertebral level.
Based on this, deduce that the needle must be inserted at a level below L2.
Evaluate the given options: L3-L4 is below L2. T1-T2 and T2-T3 are in the thoracic region, well above L2, where the cord is present. S1-S2 is in the fused sacrum, which is not a viable insertion site.

Concept Tested & Keywords

Concept Tested: Anatomical landmarks and the safe insertion site for a lumbar puncture procedure.
Stem keywords: Lumbar puncture, insertion
Lead-in keywords: commonly made at

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E6 Nelson Textbook of Pediatrics(2024) — Volume 2 p. 1363-1365

E6 Anatomy Grays 43e Vol 2 Part 2 p. 39-41