title: Altered disc compression in children with idiopathic low back pain: an upright magnetic resonance imaging backpack study.
abstract: METHODS
  This study is a repeated measures design to measure the lumbar spine's response to common backpack loads in children with idiopathic low back pain (ILBP) using upright magnetic resonance imaging (MRI).
  
  
  OBJECTIVE
  The purpose of this study is to analyze the lumbar spine's response to backpack loads with upright MRI in children with ILBP to compare their results with previously published normal child data under the same conditions. We hypothesize that typical backpack loads will have a different effect on the lumbar spine of normal children and children with ILBP.
  
  
  BACKGROUND
  Research in normal children shows that backpack loads compress the lumbar intervertebral discs (IVDs), increase lumbar coronal deformity, and increase pain.
  
  
  METHODS
  Fifteen pediatric and adolescent patients with ILBP were selected. Patients were excluded if a spinal deformity, an underlying pathology, or known injury was identified. A 0.6-T upright MRI scanner imaged the subjects while in supine and standing positions wearing 0-kg, 4-kg, and 8-kg backpacks. IVD height, lumbar lordosis, lumbar coronal deformity, and pain score were recorded after each condition and compared using analysis of variances. We compared the above-mentioned variables between ILBP and normal subjects using generalized least squares models.
  
  
  RESULTS
  The cohort's mean age was 13 ± 3 years. The 4-kg and 8-kg backpacks only compressed the L5-S1 IVD relative to upright with no load. Subjects experienced increasing pain with increasing load. Load had no effect on lumbar lordosis or lumbar coronal deformity. Compared with normal children, children with ILBP experience significantly less disc compression at T12-L1 to L4-L5, less lumbar lordosis, and more pain with increasing load.
  
  
  CONCLUSIONS
  In children with ILBP, increasing backpack load compresses only the L5-S1 IVD. Compared with normal children, children with ILBP experience less lumbar IVD compression, less lumbar lordosis, and more pain due to increasing load suggesting altered mechanisms for load tolerance in children with ILBP.
  
  
  METHODS
  3.
authors.affiliation: *Department of Orthopaedic Surgery, University of California, San Diego, CA †Rady Children's Hospital and Health Center, Department of Orthopaedic Surgery, San Diego, CA ‡Department of Radiology, Rady Children's Hospital and Health Center, University of California, San Diego, CA §University of California, Clinical and Translational Research Institute, Biostatistics Core, San Diego, CA ¶University of California, Division of Biostatistics and Bioinformatics, San Diego, CA.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Shymon
authors.forename: Burt
authors.initials: B
authors.lastname: Yaszay
authors.forename: Jerry R
authors.initials: JR
authors.lastname: Dwek
authors.forename: James A
authors.initials: JA
authors.lastname: Proudfoot
authors.forename: Michael
authors.initials: M
authors.lastname: Donohue
authors.forename: Alan R
authors.initials: AR
authors.lastname: Hargens
mesh_terms: D000293:Adolescent; D001696:Biomechanical Phenomena / Q000502:physiology; D002648:Child; D019245:Compressive Strength / Q000502:physiology; D005260:Female; D006801:Humans; D007403:Intervertebral Disc / Q000000981:diagnostic imaging*; D017116:Low Back Pain / Q000000981:diagnostic imaging* / Q000453:epidemiology; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011187:Posture / Q000502:physiology*; D011859:Radiography; D016474:Weight-Bearing / Q000502:physiology*