Lumbar Puncture: Procedure, Site, Needle Direction, and Structures Pierced

A lumbar puncture (LP), also known as a spinal tap, is a medical procedure used to collect cerebrospinal fluid (CSF) for diagnostic purposes or to administer medications. This procedure is crucial in diagnosing central nervous system infections, certain cancers, and neurological disorders.

Procedure Overview

The lumbar puncture is performed with the patient positioned either lying on their side or seated and leaning forward. The needle is inserted into the subarachnoid space between the lumbar vertebrae.

Site of Needle Insertion

• The needle is usually inserted between L3-L4 or L4-L5 intervertebral spaces to avoid injury to the spinal cord.
• The iliac crest serves as a landmark for identifying the appropriate site.

Needle Direction, Depth, and Angle Considerations

The needle should be inserted at a slight angle, typically directed towards the umbilicus.

• The depth of insertion depends on patient anatomy but averages around 4-5 cm.
• A beveled needle is preferred to minimize trauma to tissues.

Structures Pierced

1. Skin
2. Subcutaneous Tissue
3. Supraspinous Ligament
4. Interspinous Ligament
5. Ligamentum Flavum
6. Epidural Space
7. Dura Mater
8. Arachnoid Mater
9. Subarachnoid Space (CSF collection site)

Complications and Risks

While lumbar puncture is generally safe, complications can include headache, infection, bleeding, and rare neurological complications. Proper technique minimizes risks.

Conclusion

Lumbar puncture remains an essential diagnostic tool in medicine, aiding in identifying infections, bleeding, and neurological disorders.