title: The effect of backpacks on the lumbar spine in children: a standing magnetic resonance imaging study.
abstract: METHODS
  This study is a repeated measures design to measure the lumbar spine response to typical school backpack loads in healthy children. The lumbar spine in this setting was measured for the first time by an upright magnetic resonance imaging (MRI) scanner.
  
  
  OBJECTIVE
  The purpose of this study is to measure the lumbar spine response to typical school backpack loads in healthy children. We hypothesize that backpack loads significantly increase disc compression and lumbar curvature.
  
  
  BACKGROUND
  Children commonly carry school backpacks of 10% to 22% bodyweight. Despite growing concern among parents about safety, there are no imaging studies which describe the effect of backpack loads on the spine in children.
  
  
  METHODS
  Three boys and 5 girls, age 11 +/- 2 years (mean +/- SD) underwent T2 weighted sagittal and coronal MRI scans of the lumbar spine while standing. Scans were repeated with 4, 8, and 12 kg backpack loads, which represented approximately 10%, 20%, and 30% body weight for our sample. Main outcome measures were disc compression, defined as post- minus preloading disc height, and lumbar asymmetry, defined as the coronal Cobb angle between the superior endplates of S1 and L1.
  
  
  RESULTS
  Increasing backpack loads significantly compressed lumbar disc heights measured in the midline sagittal plane (P < 0.05, repeated-measures analysis of variance [ANOVA]). Lumbar asymmetry was: 2.23 degrees +/- 1.07 degrees standing, 5.46 degrees +/- 2.50 degrees with 4 kg, 9.18 degrees +/- 2.25 degrees with 8 kg, and 5.68 degrees +/- 1.76 degrees with 12 kg (mean +/- SE). Backpack loads significantly increased lumbar asymmetry (P < 0.03, one-way ANOVA). Four of the 8 subjects had Cobb angles greater than 10 degrees during 8-kg backpack loads. Using a visual-analogue scale to rate their pain (0-no pain, 10-worst pain imaginable), subjects reported significant increases in back pain associated with backpack loads of 4, 8, and 12 kg (P < 0.001, 1-way ANOVA).
  
  
  CONCLUSIONS
  Backpack loads are responsible for a significant amount of back pain in children, which in part, may be due to changes in lumbar disc height or curvature. This is the first upright MRI study to document reduced disc height and greater lumbar asymmetry for common backpack loads in children.
authors.affiliation: Department of Orthopaedic Surgery, University of California, San Diego, CA 92103, USA. tneuschwander@ucsd.edu
authors.forename: Timothy B
authors.initials: TB
authors.lastname: Neuschwander
authors.forename: John
authors.initials: J
authors.lastname: Cutrone
authors.forename: Brandon R
authors.initials: BR
authors.lastname: Macias
authors.forename: Samantha
authors.initials: S
authors.lastname: Cutrone
authors.forename: Gita
authors.initials: G
authors.lastname: Murthy
authors.forename: Henry
authors.initials: H
authors.lastname: Chambers
authors.forename: Alan R
authors.initials: AR
authors.lastname: Hargens
mesh_terms: D000293:Adolescent; D000704:Analysis of Variance; D001416:Back Pain / Q000209:etiology; D002648:Child; D005260:Female; D006801:Humans; D007403:Intervertebral Disc / Q000502:physiology*; D017770:Lifting / Q000009:adverse effects*; D008159:Lumbar Vertebrae / Q000502:physiology*; D008279:Magnetic Resonance Imaging; D008297:Male; D018579:Patient Selection; D011187:Posture / Q000502:physiology*; D012044:Regression Analysis; D016474:Weight-Bearing / Q000502:physiology*