Concordance Between Landmark-Guided and Ultrasound-Identified Lumbar Interspace in Patients with Obesity: A Prospective Observational Study

Background: Reliable identification of the lumbar interspace is essential for safe neuraxial anesthesia. Landmark-based techniques such as the Tuffier line may be unreliable in patients with obesity because excess adipose tissue obscures anatomical landmarks. Ultrasonography may improve vertebral level identification in patients with difficult anatomy. Methods: This prospective observational study evaluated concordance between landmark-guided palpation and ultrasound-confirmed lumbar interspace identification. Sixty-six adult surgical patients (33 obese and 33 nonobese controls) with American Society of Anesthesiologists physical status I–III scheduled for elective procedures were prospectively enrolled. Landmark-based identification directed at the presumed L4–L5 interspace was performed independently by three specialist anesthesiologists in both the sitting and lateral decubitus positions. Ultrasound confirmation was conducted by a blinded senior specialist anesthesiologist. Primary outcomes were exact interspace concordance rates and predictors of discordance. Results: Concordance in the sitting position was 35.5% (11/31; 95% confidence intervals [CI] 21.1–53.1) in assessable patients with obesity and 84.8% (28/33; 95% CI: 69.1–93.3) in nonobese controls (absolute risk difference [RD]: 49.3%, 95% CI: 27.8–70.8%; p < 0.001 ). In the lateral position, concordance rates were 25.8% (8/31; 95% CI: 13.7–43.2) and 78.8% (26/33; 95% CI: 62.2–89.3), respectively (absolute RD: 53.0%, 95% CI: 31.8–74.2%; p < 0.001 ). In the obesity group, palpation identified a more cranial interspace than ultrasound in 54.8% (17/31) of cases. In multivariable generalized estimating equation analysis, central obesity (adjusted odds ratio [OR] 5.95; 95% CI: 1.02–34.84; p = 0.048 ) and higher Karraz palpation difficulty grade (adjusted OR 3.02 per grade increase; 95% CI: 1.02–8.96; p = 0.047 ) were independent predictors of discordance. Conclusions: Landmark-guided identification of lumbar interspaces shows substantially lower concordance with ultrasound in patients with obesity, predominantly identifying a more cranial interspace. Such cranial misidentification, if used to guide neuraxial needle placement, may increase the potential risk of unintended higher-level puncture and complications. Preprocedural ultrasound should be considered to enhance anatomical verification in this challenging cohort.