title: A prospective, observational study of the relationship between body mass index and depth of the epidural space during lumbar transforaminal epidural steroid injection.
abstract: OBJECTIVE
  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).
  
  
  CONCLUSIONS
  There is a positive association between BMI and transforaminal epidural depth, but not with age, sex, race, oblique angle, or intervertebral level.
authors.affiliation: Division of Pain Medicine, Department of Anesthesiology, University of Michigan, Ann Arbor, MI 48109, USA.
authors.forename: Chad M
authors.initials: CM
authors.lastname: Brummett
authors.forename: Bryan S
authors.initials: BS
authors.lastname: Williams
authors.forename: Robert W
authors.initials: RW
authors.lastname: Hurley
authors.forename: Michael A
authors.initials: MA
authors.lastname: Erdek
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015992:Body Mass Index; D002648:Child; D004824:Epidural Space / Q000033:anatomy & histology*; D005260:Female; D006801:Humans; D007268:Injections, Epidural; D017116:Low Back Pain / Q000188:drug therapy; D008161:Lumbosacral Region / Q000033:anatomy & histology; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D013256:Steroids / Q000008:administration & dosage*; D055815:Young Adult
chemical_list: D013256:Steroids