title: Lumbar spine disc height and curvature responses to an axial load generated by a compression device compatible with magnetic resonance imaging.
abstract: METHODS
  Axial load-dependent changes in the lumbar spine of supine healthy volunteers were examined using a compression device compatible with magnetic resonance imaging.
  
  
  OBJECTIVE
  To test two hypotheses: Axial loading of 50% body weight from shoulder to feet in supine posture 1) simulates the upright lumbar spine alignment and 2) decreases disc height significantly.
  
  
  BACKGROUND
  Axial compression on the lumbar spine has significantly narrowed the lumbar dural sac in patients with sciatica, neurogenic claudication or both.
  
  
  METHODS
  Using a device compatible with magnetic resonance imaging, the lumbar spine of eight young volunteers, ages 22 to 36 years, was axially compressed with a force equivalent to 50% of body weight, approximating the normal load on the lumbar spine in upright posture. Sagittal lumbar magnetic resonance imaging was performed to measure intervertebral angle and disc height before and during compression.
  
  
  RESULTS
  Each intervertebral angle before and during compression was as follows: T12-L1 (-0.8 degrees +/- 2.5 degrees and -1.5 degrees +/- 2.6 degrees ), L1-L2 (0.7 degrees +/- 1.4 degrees and 3.3 degrees +/- 2.9 degrees ), L2-L3 (4.7 degrees +/- 3.5 degrees and 7.3 degrees +/- 6 degrees ), L3-L4 (7.9 degrees +/- 2.4 degrees and 11.1 degrees +/- 4.6 degrees ), L4-L5 (14.3 degrees +/- 3.3 degrees and 14.9 degrees +/- 1.7 degrees ), L5-S1 (25.8 degrees +/- 5.2 degrees and 20.8 degrees +/- 6 degrees ), and L1-S1 (53.4 degrees +/- 11.9 degrees and 57.3 degrees +/- 16.7 degrees ). Negative values reflect kyphosis, and positive values reflect lordosis. A significant difference between values before and during compression was obtained at L3-L4 and L5-S1. There was a significant decrease in disc height only at L4-L5 during compression.
  
  
  CONCLUSIONS
  The axial force of 50% body weight in supine posture simulates the upright lumbar spine morphologically. No change in intervertebral angle occurred at L4-L5. However, disc height at L4-L5 decreased significantly during compression.
authors.affiliation: Department of Orthopaedics, University of California-San Diego, 350 Dickinson Street, 8894 San Diego, CA 92103-8894, USA.
authors.forename: S
authors.initials: S
authors.lastname: Kimura
authors.forename: G C
authors.initials: GC
authors.lastname: Steinbach
authors.forename: D E
authors.initials: DE
authors.lastname: Watenpaugh
authors.forename: A R
authors.initials: AR
authors.lastname: Hargens
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000033:anatomy & histology*; D008279:Magnetic Resonance Imaging; D008297:Male; D009983:Orthopedic Equipment; D012016:Reference Values; D013131:Spine / Q000033:anatomy & histology* / Q000502:physiology*; D016474:Weight-Bearing / Q000502:physiology*