title: The role of obesity in the biomechanics and radiological changes of the spine: an in vitro study.
abstract: OBJECTIVE
  The effects of obesity on lumbar biomechanics are not fully understood. The aims of this study were to analyze the biomechanical differences between cadaveric L4-5 lumbar spine segments from a large group of nonobese (body mass index [BMI] < 30 kg/m2) and obese (BMI ≥ 30 kg/m2) donors and to determine if there were any radiological differences between spines from nonobese and obese donors using MR imaging.
  
  
  METHODS
  A total of 168 intact L4-5 spinal segments (87 males and 81 females) were tested using pure-moment loading, simulating flexion-extension, lateral bending, and axial rotation. Axial compression tests were performed on 38 of the specimens. Sex, age, and BMI were analyzed with biomechanical parameters using 1-way ANOVA, Pearson correlation, and multiple regression analyses. MR images were obtained in 12 specimens (8 from obese and 4 from nonobese donors) using a 3-T MR scanner.
  
  
  RESULTS
  The segments from the obese male group allowed significantly greater range of motion (ROM) than those from the nonobese male group during axial rotation (p = 0.018), while there was no difference between segments from obese and nonobese females (p = 0.687). There were no differences in ROM between spines from obese and nonobese donors during flexion-extension or lateral bending for either sex. In the nonobese population, the ROM during axial rotation was significantly greater for females than for males (p = 0.009). There was no significant difference between sexes in the obese population (p = 0.892). Axial compressive stiffness was significantly greater for the obese than the nonobese population for both the female-only group and the entire study group (p < 0.01); however, the difference was nonsignificant in the male population (p = 0.304). Correlation analysis confirmed a significant negative correlation between BMI and resistance to deformation during axial compression in the female group (R = -0.65, p = 0.004), with no relationship in the male group (R = 0.03, p = 0.9). There was also a significant negative correlation between ROM during flexion-extension and BMI for the female group (R = -0.38, p = 0.001), with no relationship for the male group (R = 0.06, p = 0.58). Qualitative analysis using MR imaging indicated greater facet degeneration and a greater incidence of disc herniations in the obese group than in the control group.
  
  
  CONCLUSIONS
  Based on flexibility and compression tests, lumbar spinal segments from obese versus nonobese donors seem to behave differently, biomechanically, during axial rotation and compression. The differences are more pronounced in women. MR imaging suggests that these differences may be due to greater facet degeneration and an increased amount of disc herniation in the spines from obese individuals.
authors.affiliation: Divisions of 1 Neurological Surgery and.
authors.forename: Nestor G
authors.initials: NG
authors.lastname: Rodriguez-Martinez
authors.affiliation: Divisions of 1 Neurological Surgery and.
authors.forename: Luis
authors.initials: L
authors.lastname: Perez-Orribo
authors.affiliation: Divisions of 1 Neurological Surgery and.
authors.forename: Samuel
authors.initials: S
authors.lastname: Kalb
authors.affiliation: Divisions of 1 Neurological Surgery and.
authors.forename: Phillip M
authors.initials: PM
authors.lastname: Reyes
authors.affiliation: Divisions of 1 Neurological Surgery and.
authors.forename: Anna G U S
authors.initials: AG
authors.lastname: Newcomb
authors.affiliation: Neuroradiology, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, Arizona.
authors.forename: Jeremy
authors.initials: J
authors.lastname: Hughes
authors.affiliation: Divisions of 1 Neurological Surgery and.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Theodore
authors.affiliation: Divisions of 1 Neurological Surgery and.
authors.forename: Neil R
authors.initials: NR
authors.lastname: Crawford
mesh_terms: D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena / Q000502:physiology; D015992:Body Mass Index; D005260:Female; D006801:Humans; D007405:Intervertebral Disc Displacement / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000601:surgery*; D008161:Lumbosacral Region / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications*; D018583:Pliability / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology*; D012399:Rotation; D013123:Spinal Fusion / Q000379:methods
keywords: BMD = bone mineral density; BMI = body mass index; ROM = range of motion; biomechanics; flexibility; lumbar spine; obesity