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A Prospective, Observational Study of the Relationship Between Body Mass Index and Depth of the Epidural Space During Lumbar Transforaminal Epidural Steroid Injection
  1. Chad M. Brummett, MD*,
  2. Bryan S. Williams, MD,
  3. Robert W. Hurley, MD, PhD and
  4. Michael A. Erdek, MD
  1. From the *Division of Pain Medicine, Department of Anesthesiology, University of Michigan, Ann Arbor, MI; and
  2. Division of Pain Medicine, Department of Anesthesiology & Critical Care Medicine, The Johns Hopkins University, Baltimore, MD.
  1. Address correspondence to: Chad M. Brummett, MD, Department of Anesthesiology, University of Michigan Health System, 1500 East Medical Center Dr, 1H247 UH, Box 0048, Ann Arbor, MI 48109.


Background and Objectives: Previous studies have concluded that transforaminal epidural steroid injections (ESIs) are more effective than interlaminar injections in the treatment of radiculopathies due to lumbar intervertebral disk herniation. There are no published studies examining the depth of epidural space using a transforaminal approach. We investigated the relationship between body mass index (BMI) and the depth of the epidural space during lumbar transforaminal ESIs.

Methods: Eighty-six consecutive patients undergoing lumbar transforaminal ESI at the L3-L4, L4-L5, and L5-S1 levels were studied. Using standard protocol, the foraminal epidural space was attained using fluoroscopic guidance. The measured distance from needle tip to skin was recorded (depth to foraminal epidural space). The differences in the needle depth and BMI were analyzed using regression analysis.

Results: Needle depth was positively associated with BMI (regression coefficient [RC], 1.13; P < 0.001). The median depths (in centimeters) to the epidural space were 6.3, 7.5, 8.4, 10.0, 10.4, and 12.2 for underweight, normal, preobese, obese I, obese II, and obese III classifications, respectively. Sex (RC, 1.3; P = 0.02) and race (RC, 0.8; P = 0.04) were also significantly associated with needle depth; however, neither factor remained significant when BMI was accounted as a covariate in the regression model. Age, intervertebral level treated, and oblique angle had no predictive value on foraminal depth (P > 0.2).

Conclusion: There is a positive association between BMI and transforaminal epidural depth, but not with age, sex, race, oblique angle, or intervertebral level.

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  • This study was performed at The Johns Hopkins Medical Institutes, Baltimore, MD.

  • This study was funded in part through an unrestricted educational grant from Alpharma Inc. Further support was provided by NIH grant no. MH075884 (to R.W.H) and the IASP Trainee Fellowship funded by the Scan/Design by Jens and Inger Bruun Foundation (to R.W.H.).