From Palpation to Visualization:

For many clinicians, the lumbar puncture (LP) is a core procedure learned by feel. Training traditionally focuses on palpating for the iliac crests, finding the L3-L4 interspace, and advancing the needle, guided by tactile feedback—the subtle “pop” of the ligamentum flavum. When successful, it’s a smooth, effective diagnostic. But what about when it’s not?

It may be a familiar frustration for many clinicians: an attempt based on palpation that hits bone, requires multiple redirections, or results in a traumatic tap. These challenges are increasingly common. With some U.S. states reaching close to 50% prevalence in obesity, a reliance on palpating landmarks becomes increasingly ripe for adverse events (AEs).

The traditional, landmark-based technique isn’t necessarily failing because of a lack of skill; it’s failing because it relies on “guessing” the anatomy beneath the skin. This presents an opportunity to evolve from a procedure of palpation to one of visualization.

The Problem with Palpation-Only Procedures

The core assumption of the landmark-based LP is that what is felt is accurately sufficient to determine the spinal level, confirm the midline, as well as estimate the depth from skin to the dura. However, this is not backed by the literature.

• Palpation is Often Inaccurate: Studies have shown that even in lean patients, identifying the correct interspinous space by palpation alone is notoriously unreliable.^1,2
• The BMI Challenge: In patients with a high BMI, palpating landmarks becomes exponentially more difficult, if not impossible. One study found that while pertinent landmarks were palpable in 95% of normal-BMI patients, they were only palpable in 32% of obese patients.³
• The Cost of Failure: A failed attempt by feel isn’t just an inconvenience. It leads to multiple painful attempts for the patient, increased risk of a traumatic tap (which can confound results), procedure delays, and potential escalation to fluoroscopic guidance, which costs time and exposes the patient to radiation.

Relying on feel alone is to operate by touch. POCUS allows the clinician to operate by sight, replacing anatomical guesswork with visual data.

The POCUS Advantage: Seeing the Unseeable

Using ultrasound for an LP isn’t just about “finding the spot.” It’s about pre-procedural mapping that transforms the anatomical landscape from a guess into a certainty. It provides critical data that palpation simply cannot.

• Finding the True Midline: Ultrasound in the transverse view shows the spinous process as a bright line with a shadow behind it. This lets you mark the true midline instead of guessing by touch—especially helpful when landmarks are hard to feel.
• Selecting the Widest Interspace: Move slightly off the midline and rotate the probe into a paramedian sagittal oblique view. This view shows the “gaps” between the bones (interlaminar spaces). You simply pick the widest, clearest gap—often L3–4 or L4–5—before you start the procedure.
• Measuring the Exact Depth: This may be the most critical advantage. POCUS allows the clinician to measure the distance from the skin to the ligamentum flavum. Studies show this depth varies significantly by body habitus—from an average of 44 mm in normal-BMI patients to 64 mm or more in obese patients.³ Knowing this depth before needle insertion informs needle selection and indicates exactly how far to advance, minimizing the risk of over-shooting or hitting bone.
• Detecting Anatomical “Roadblocks”: Does the patient have hidden scoliosis? Degenerative changes? Hardware from a previous surgery? POCUS can identify these anatomical variations before the procedure begins, allowing the clinician to adjust their approach or determine if the procedure is even feasible at the bedside.

From Difficult to Routine

The evidence supporting POCUS for LPs is overwhelming in obese or difficult to palpate patients. A systematic review and meta-analysis of 14 randomized controlled trials found that ultrasound guidance significantly decreased the risk of failed procedures, reduced the number of insertion attempts, and lowered the risk of traumatic taps.¹

This data has led many experts to advocate for the routine use of ultrasound in all patients, not just those with difficult-to-palpate landmarks. Why? Because POCUS provides more anatomical information than palpation alone.² It builds a margin of safety and success into every single procedure.

This shift mirrors the one championed by surgeons like Dr. Josè Pinto, who argues that POCUS should be considered the “fifth pillar” of the physical examination.⁴ He notes that clinicians were once taught to “see with their fingertips,” but with ultrasound, he can “see beyond” what his hands can perceive.⁴

Closing the Gap

If the evidence is so clear, why isn’t POCUS-guided LP the universal standard? The most significant barrier is often the “training gap.”

However, that barrier is shrinking. As POCUS technology becomes more intuitive, portable, and powerful, its adoption is accelerating. New systems are increasingly designed to flatten the learning curve, offering features like real-time guidance and anatomical labeling that help build clinician confidence.

The lumbar puncture doesn’t have to be an anxiety-provoking procedure based on palpation. By incorporating POCUS, it can be transformed into a confident, precise, and anatomy-based intervention, improving patient safety and diagnostic success with every tap.

The Right Tool for Visualizing Anatomy

Performing this kind of detailed pre-procedural mapping requires a high-resolution linear probe. EchoNous designed and manufactures the Kosmos Lexsa, which is a 64/128 channel linear probe specifically optimized for applications that require outstanding image clarity, including nerve, vascular, and musculoskeletal (MSK) imaging. Its technical specifications, such as a 3-10.5 MHz frequency range and a scan depth of up to 10 cm, make it well-suited for visualizing the superficial spinal anatomy necessary for a POCUS-guided lumbar puncture.

If you are interested in demoing the Kosmos Lexsa probe in your practice, drop us a line on our contact form and an ultrasound expert will get in touch!

Q&A: POCUS for Lumbar Puncture

References

1. Gottlieb M, Holladay D, Peksa GD. Ultrasound-assisted lumbar punctures: a systematic review and meta-analysis. Acad Emerg Med. 2018.
2. Soni NJ, Franco-Sadud R, Schnobrich D, et al. Ultrasound guidance for lumbar puncture. Neur Clin Pract. 2016;6(4):358-368. doi:10.1212/CPJ.0000000000000265
3. Ultrasound-guided lumbar puncture. Emory School of Medicine: Department of Emergency Medicine. Published February 2012. Accessed November 3, 2025. https://med.emory.edu/departments/emergency-medicine/sections/ultrasound/case-of-the-month/procedures/ultrasound_guided_lumbar_puncture.html
4. Dr. Josè Pinto: A Surgeon’s Perspective on the Evolution of POCUS and Trauma Assessment. Interview published on EchoNous.com. Accessed November 3, 2025.  https://echonous.com/dr-jose-pinto/