Body Mass Index Correlates with Skin to Spinal Canal Distance: A Large Retrospective Single‐Center Study

ABSTRACT BACKGROUND AND PURPOSE Despite increasing demand for fluoroscopy‐guided lumbar puncture (FG‐LP), there is limited quantitative and epidemiological data on patients undergoing this procedure. Additionally, data are scarce on the correlation of iliac crest landmarks to the actual anatomical lumbar level (intercristal line). The aim of this study is to determine if (1) body mass index (BMI) correlates with skin to spinal canal distance (SCD) and (2) the iliac crest landmark correlates with the presumed anatomical landmark on cross‐sectional imaging. METHODS In this retrospective, single‐center IRB‐approved study, we assessed 495 patients who underwent FG‐LP and had lumbar computed tomography/magnetic resonance imaging within 6 months of presentation. SCD was measured on the sagittal view at the L3‐L4, L4‐L5, and L5‐S1 intervertebral levels. RESULTS In our cohort of 495 adults (mean age ± standard deviation [SD], 53.2 ± 16.4 years), there was a statistically significant linear correlation between BMI and SCD at each intervertebral level. Mean ± SD (R2) SCD at L3‐4, L4‐5, and L5‐S1 was 6.7 ± 1.6 cm (.5486), 7.4 ± 1.9 cm (.5894), and 7.8 ± 1.9 cm (.5968), respectively. The intercristal line aligned with L3‐L4, L4‐L5, and L5‐S1 in 2.1%, 72.4%, and 6.2% of patients, respectively. CONCLUSIONS There was direct, positive linear correlation between BMI and SCD at clinically relevant lumbar disc levels. Furthermore, there is considerable anatomical variance in the intervertebral space that aligns with the superior aspect of the iliac crest.