Lumbar Puncture : Procedure

Lumbar puncture is a medical procedure to check for cerebrospinal fluid infection. Infection in the CSF is very dangerous and can be fatal. The main sites where lumbar puncture is done are L3, L4, and L5.

The patient is laid in a flexion posture by flexing the spine. This creates gaps in the vertebral spine to insert the needle. Mark the highest point of the iliac crest, which is at the level of the L4 vertebra spine. Then, the needle is Pushed to the highest point of the iliac crest in the L4,5 space. 

Intervertebral Ligaments and Disc

As we are puncturing delicate structures, it is very important to understand the anatomy of the intervertebral ligaments and discs. 

The anterior longitudinal ligament is present in the front of the vertebral body, and the Posterior longitudinal ligament is present behind it. Some ligaments are in front of and behind the body. Ligamentum flavum is between the Lamina of the vertebra. It is behind the body.

The ligamentum flavum connects the Lamina1 vertebra to the other vertebra. The spine of the vertebra is connected with the supraspinous ligament and interspinous ligament. We have to puncture them by pushing the needle.

To reach the spinal cord, we have to puncture the ligamentum flavum, supraspinous ligament, and interspinous ligament. We have to do the puncture below the spinal cord, below the L1 vertebra.

Procedure of Lumbar Puncture

• Push the needle between the L4 and L4 vertebra. This space is an interspinous space.
• Supraspinous, interspinous, and ligamentum flavum are punctured.
• Next in line, the dura mater and the arachnoid membrane are punctured 
• While puncturing through the ligament, the needle gets resistant.
• The sudden loss of resistance to the puncturing needle is called a popping sensation. 
• The second popping sensation happens after puncturing the dura mater. Resistance occurs while puncturing the dura mater.
• Puncturing the posterior longitudinal ligament is a mistake.
• New learner’s do that by pushing forward. We are not supposed to enter the anterior longitudinal ligament. 

Needle Puncturing

Needle is puncturing the two meninges, dura, and arachnoid. You have to vacate the CSF.

Popping sensations are observed. L4, L5, spine of vertebra are drawn. Lamina is drawn in between.

Anterior longitudinal ligament is present in front of the vertebra. Posterior longitudinal ligament is present behind the vertebra. Ligamentum flavum is present between the Lamina. Interspinous ligament is present in between the spine. Supraspinous is present at the tip of the spine.

The Order to Puncture the Parts

• Supraspinous 
• Interspinous 
• Ligamentum flavum
• Meninges, dura, and arachnoid

If you puncture the posterior longitudinal ligament, it is accidental. After puncturing the dura and arachnoid, enter the subarachnoid space to vacate the CSF and inject the anesthetic agent.

Anterior longitudinal ligament can never be reached. We would puncture the ligamentum flavum and Supraspinous regularly. If we reach the posterior ligament then it is accidental.

Frequently Asked Questions

Q: During a procedure to remove cerebrospinal fluid from the subarachnoid space below the end of the spinal cord, the needle was advanced too far and penetrated the ligament forming the anterior border of the vertebral canal. Which of the following ligaments, not normally pierced during this procedure, was accidentally penetrated? 

1. Anterior longitudinal 
2. Ligamentum Flava
3. Posterior longitudinal 
4. Supraspinous

Answer: c.   Posterior longitudinal.

Q: Popping sensation felt on doing Lumbar puncture is while piercing 

1. Ligamentum flavum 
2. Supraspinous ligament 
3. Interspinous ligament 
4. Duramater

Answer: Ligamentum flavum (considered correct by majority) and Duramater (considered correct by minority).

Q: Which layer is present between the Lamina?

Answer: Ligamentum flavum 

Also Read: Hematopoiesis: The Journey Of Blood Cell Production

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