Intraspinal medication is given in which IVD space?

AIIMS Delhi NO - 2017

Applied Physiology

Easy

Appeared in: AIIMS Delhi NO - 2017

Explanation

Intraspinal medication is administered into the subarachnoid space, a procedure known as lumbar puncture.
The L4-L5 intervertebral space is the most common and safest site for this procedure in adults.
This location is chosen because the spinal cord (conus medullaris) typically terminates at the L1-L2 vertebral level, so an injection at L4-L5 minimizes the risk of spinal cord injury.
A key anatomical landmark, Tuffier's line (an imaginary line connecting the iliac crests), passes through the L4 vertebra or the L4-L5 space, making it easy to locate.

Option B: This is the level where the spinal cord (conus medullaris) typically terminates in adults. Inserting a needle at this level carries a very high risk of causing direct, irreversible trauma to the spinal cord.
Option C: The human vertebral column does not have L6 or L7 vertebrae. The lumbar spine consists of five vertebrae, L1 through L5, followed by the sacrum.
Option D: While a lumbar puncture can occasionally be performed at the L2-L3 space, it is less desirable and less safe than the L3-L4 or L4-L5 spaces. It is closer to the conus medullaris, increasing the risk of injury, especially in individuals whose spinal cord extends slightly lower than average.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Anatomical landmarks for intraspinal medication administration as background academic context rather than a clinical decision trigger.
Correctly identifying the L4-L5 interspace is a critical skill for nurses and physicians to ensure patient safety during procedures like spinal anesthesia, diagnostic lumbar punctures (for CSF analysis), and administration of intrathecal chemotherapy.
Incorrect needle placement can lead to severe complications, including direct spinal cord trauma, nerve root damage, hematoma formation, infection, and debilitating post-dural puncture headaches.
What if the patient is an infant? In infants and young children, the spinal cord ends at a lower level (around L3). Therefore, the puncture is performed at an even lower space, such as L4-L5 or L5-S1, to maintain a safe margin from the cord.

How to Approach the Question

First, identify the core of the question: it asks for the correct anatomical location for an 'intraspinal' injection.
Recall the key anatomical principle for this procedure: to avoid injuring the spinal cord, the needle must be inserted below the point where the cord terminates.
Remember that in adults, the spinal cord (conus medullaris) typically ends at the L1-L2 vertebral level.
Evaluate the given options based on this safety principle. Eliminate L1-L2 as it is too high and dangerous. Eliminate L6-L7 as it is anatomically non-existent.
Compare the remaining viable options, L2-L3 and L4-L5. Both are below the L1-L2 level.
Select L4-L5 as the best answer because it is the lowest of the two, providing the largest margin of safety from the spinal cord. It is also the most common site used in clinical practice, easily located by palpating the iliac crests.

Concept Tested & Keywords

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