title: Body posture and backpack loading: an upright magnetic resonance imaging study of the adult lumbar spine.
abstract: OBJECTIVE
  Axial loading of the spine while supine, simulating upright posture, decreases intervertebral disc (IVD) height and lumbar length and increases lumbar lordosis. The purpose of this study is to measure the adult lumbar spine's response to upright posture and a backpack load using upright magnetic resonance imaging (MRI). We hypothesize that higher spinal loads, while upright and with a backpack, will compress lumbar length and IVD height as well as decrease lumbar lordosis.
  
  
  METHODS
  Six volunteers (45 ± 6 years) underwent 0.6 T MRI scans of the lumbar spine while supine, upright, and upright with a 10 % body weight (BW) backpack. Main outcomes were IVD height, lumbar spinal length (distance between anterior-superior corners of L1 and S1), and lumbar lordosis (Cobb angle between the superior endplates of L1 and S1).
  
  
  RESULTS
  The 10 % BW load significantly compressed the L4-L5 and L5-S1 IVDs relative to supine (p < 0.05). The upright and upright plus 10 % BW backpack conditions significantly compressed the anterior height of L5-S1 relative to supine (p < 0.05), but did not significantly change the lumbar length or lumbar lordosis.
  
  
  CONCLUSIONS
  The L4-L5 and L5-S1 IVDs compress, particularly anteriorly, when transitioning from supine to upright position with a 10 % BW backpack. This study is the first radiographic analysis to describe the adult lumbar spine wearing common backpack loads. The novel upright MRI protocol described allows for functional, in vivo, loaded measurements of the spine that enables the study of spinal biomechanics and therapeutic interventions.
authors.affiliation: Department of Orthopaedic Surgery, University of California, San Diego, 350 Dickinson Street, Suite 121, San Diego, CA, 92103-8894, USA.
authors.forename: Stephen
authors.initials: S
authors.lastname: Shymon
authors.forename: Alan R
authors.initials: AR
authors.lastname: Hargens
authors.forename: Lawrence A
authors.initials: LA
authors.lastname: Minkoff
authors.forename: Douglas G
authors.initials: DG
authors.lastname: Chang
mesh_terms: D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D007403:Intervertebral Disc / Q000502:physiology*; D008159:Lumbar Vertebrae / Q000502:physiology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D011187:Posture / Q000502:physiology*; D016474:Weight-Bearing / Q000502:physiology*