What are the recommended landmarks for a lumbar puncture (lumbar puncture)?

Recommended Landmarks for Lumbar Puncture

For lumbar puncture, the recommended landmark is to identify the L3-L4 or L4-L5 intervertebral space using the intercristal line (connecting the superior aspects of both iliac crests) which typically crosses the spine at the L4 vertebra or L4-L5 interspace. 1

Anatomical Landmarks and Positioning

Primary Landmarks

• Intercristal line (Tuffier's line): The line connecting the superior aspects of both iliac crests
  • This line typically crosses the spine at the L4 vertebra or L4-L5 interspace
  • Use this line to identify the L4-L5 interspace, then count up or down for other levels
• Spinous processes: Palpate to identify the interspaces between vertebrae
• Recommended puncture sites: L3-L4 or L4-L5 interspace (below the termination of the spinal cord)

Patient Positioning

• Lateral decubitus position: Patient lying on side with knees drawn to chest and back at edge of bed
• Sitting position: Patient sitting with feet supported and leaning forward to maximize opening of interspaces

Important Considerations

Limitations of Anatomical Landmarks

• Clinical landmark identification is inaccurate in approximately 30-36% of cases 1, 2
• The intercristal line may cross anywhere from L2/3 to L5/S1, with significant variability 2
• The conus medullaris (end of spinal cord) may extend as low as L3 in some patients, particularly neonates 2

Needle Selection and Insertion

• Strongly recommended: Use atraumatic (pencil-point) needles rather than conventional cutting needles 3
  • Atraumatic needles reduce post-dural puncture headache by 60% (from 98 to 39 per 1000 procedures) 3
  • These needles separate and dilate dural fibers rather than cutting through them 3
• If using a cutting needle, insert with the bevel parallel to the long axis of the spine to reduce risk of post-dural puncture headache 3

Ultrasound Guidance

• Recommended for patients with difficult-to-palpate landmarks or obesity 4
• Ultrasound guidance can:
  • Reduce needle insertion attempts and redirections
  • Increase overall procedure success rates
  • More accurately identify lumbar spine level than physical examination
  • Estimate needle insertion depth 4

Procedural Recommendations

Ultrasound Technique (When Available)

1. Use a low-frequency curvilinear transducer (high-frequency linear array may be used in non-obese patients)
2. Map the lumbar spine starting at the sacrum and moving cephalad
3. Use transverse plane to mark midline and longitudinal plane to mark interspinous spaces
4. Mark the intersection of these lines as the needle insertion site
5. Measure the distance from skin to ligamentum flavum to estimate needle depth 4

When Performing Epidural Blood Patch

• When the site of dural puncture is known, perform the epidural blood patch at or one space below this level 3
• Consider radiologic guidance based on patient factors including age, BMI, degree of spondylotic change, and prior lumbar spine surgery 3

Pitfalls and Caveats

• Relying solely on palpation of landmarks can lead to selection of an inappropriate intervertebral level in up to 36% of cases 1, 2
• No specific patient parameters reliably predict which patients will have inaccurate landmark identification 1
• In neonates, the conus medullaris may extend lower (to L2 or below in 36% of cases), increasing risk of spinal cord damage with incorrect level identification 2
• Routine ultrasound for all lumbar punctures may not provide significant advantage in patients with easily palpable landmarks 5

By following these landmark identification techniques and considering ultrasound guidance when appropriate, clinicians can maximize success rates and minimize complications associated with lumbar puncture.