title: Using Body Mass Index to Predict Needle Length in Fluoroscopy-Guided Lumbar Punctures.
abstract: OBJECTIVE
  Predicting the appropriate needle length to use in oblique interlaminar-approach fluoroscopy-guided lumbar punctures in patients with a large body mass index is difficult. Using the wrong needle length can lead to an increased radiation dose and patient discomfort. We hypothesized that body mass index could help determine the appropriate needle length to use in patients.
  
  
  METHODS
  We randomly selected patients who underwent oblique interlaminar-approach fluoroscopy-guided lumbar punctures and had cross-sectional imaging of the lumbar spine within 1 year of imaging (n = 50). The distance from the skin to the midlumbar spinal canal (skin-canal distance) at the level of the lumbar puncture was measured by using an oblique angle of 8.6°, which is an average of angles most often used to perform the procedure. A formula was devised using the skin-canal distance and body mass index to predict the appropriate needle length, subsequently confirmed in 45 patients.
  
  
  RESULTS
  The body mass index and skin-canal distance were significantly higher (P < .001) in patients who underwent fluoroscopy-guided lumbar puncture with 5- or 7-inch needles (n = 22) than in patients requiring 3.5-inch needles (n = 28). Using linear regression, we determined the formula to predict the needle length as Skin-Canal Distance (inches) = 0.077 × Body Mass Index + 0.88. We found a strong correlation (P < .001) between the predicted and actual skin canal distance in 45 patients, and our formula better predicted the skin-canal distance than others.
  
  
  CONCLUSIONS
  We designed a formula that uses body mass index to predict the appropriate needle length in oblique interlaminar-approach fluoroscopy-guided lumbar punctures and validated it by demonstrating a strong correlation between the predicted and actual skin-canal distance.
authors.affiliation: From the Department of Radiology, Division of Neuroradiology, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: A P
authors.identifier: http://orcid.org/0000-0001-6846-2074
authors.initials: AP
authors.lastname: Nayate
authors.affiliation: From the Department of Radiology, Division of Neuroradiology, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: I M
authors.identifier: http://orcid.org/0000-0003-2346-7562
authors.initials: IM
authors.lastname: Nasrallah
authors.affiliation: From the Department of Radiology, Division of Neuroradiology, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: J E
authors.identifier: http://orcid.org/0000-0002-7487-227X
authors.initials: JE
authors.lastname: Schmitt
authors.affiliation: From the Department of Radiology, Division of Neuroradiology, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania. suyash.mohan@uphs.upenn.edu.
authors.forename: S
authors.identifier: http://orcid.org/0000-0002-4025-115X
authors.initials: S
authors.lastname: Mohan
mesh_terms: D000328:Adult; D015992:Body Mass Index; D005260:Female; D005471:Fluoroscopy / Q000379:methods; D006801:Humans; D016014:Linear Models; D008159:Lumbar Vertebrae; D008297:Male; D008875:Middle Aged; D009339:Needles; D013129:Spinal Puncture / Q000295:instrumentation* / Q000379:methods*