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1295. Body Mass Index Correlates with Skin to Spinal Canal Distance: A Large Retrospective Single-Center Study
Authors * Denotes Presenting Author
  1. Keon Mahmoudi *; Icahn School of Medicine at Mount Sinai
  2. Young Joon (Fred) Kwon; Icahn School of Medicine at Mount Sinai
  3. Shingo Kihira; Icahn School of Medicine at Mount Sinai
  4. Puneet Belani; Icahn School of Medicine at Mount Sinai
  5. Thomas Naidich; Icahn School of Medicine at Mount Sinai
  6. Anthony Costa; Icahn School of Medicine at Mount Sinai
  7. Amish Doshi; Icahn School of Medicine at Mount Sinai
Objective:
Diagnostic lumbar puncture (LP) is one of the most commonly performed procedures in clinical medicine in the United States; of an estimated 135 million hospitalizations annually (emergency department [ED] + admission, or ED only), there is an estimated total of 400,000 LPs performed including blind and image-guided procedures.[1] When difficulty is encountered with bedside LP, a fluoroscopy-guided lumbar puncture (FG-LP), performed by a radiologist, is often considered. Despite increasing demand for FG-LP,[2] 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.

Materials and Methods:
In this retrospective, single-center IRB-approved study, we assessed 495 patients from one New York City hospital who underwent FG-LP and had lumbar computed tomography (CT) or magnetic resonance imaging (MRI) within 6 months of presentation. Skin to spinal canal distance was measured on the sagittal view at the L3-L4, L4-L5, and L5-S1 intervertebral levels. The lumbar level intersecting the horizontal line formed by the superior aspect of the iliac crests posteriorly, also known as the intercristal line, was identified by correlating findings on coronal and sagittal planes of CT or MRI.

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 (R^2) 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.

Conclusion:
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. Knowing a patient's BMI before the procedure may guide clinicians to select appropriate needle length and increase the success rate of LP procedures. The process of obtaining a patient's BMI is also less resource intensive than an imaging study. Furthermore, understanding the considerable anatomical variance of the iliac crest landmark may help identify strategies for more successful bedside attempts in the future.