title: Finite element analysis in adjacent segment degeneration after lumbar fusion.
abstract: BACKGROUND
  Adjacent segment degeneration (ASD) following lumbar fusion has been well documented in recent years. However, the pathogenesis of ASD is not clear. To investigate this issue, we established a finite element model of segments L2-L5, simulated a single-segment posterior fixation in L3-L4 and investigated the stress variation and the effects of the instrumented lumbar posterior fixation on adjacent levels.
  
  
  METHODS
  Models A, B and C of L2-L5 multisegment finite element intact models were established. In model A, segment L3-L4 was not fixed and was without disc degeneration in the adjacent segment (L2-L3, L4-L5); in model B there was posterior pedicle fixation in segment L3-L4 without disc degeneration in the adjacent segment (L2-L3, L4-L5); in model C there was posterior pedicle fixation in segment L3-L4 with a degenerated disc in the adjacent segment (L2-L3, L4-L5). Four levels of axial pressure, 0.3, 0.5, 1.0 and 2.0 MPa, were compared between each model of the stress variation on the discs of the adjacent segment (L2-L3, L4-L5).
  
  
  RESULTS
  The maximum principal stress mean value of disc L2-L3 under four pressures in model A was determined. The statistical results showed that stress was not significant difference in disc L2-L3 between models A and B, but there was a significant difference in disc L2-L3 between models A and C and a significant difference between each group in disc L4-L5 under four pressure conditions.
  
  
  CONCLUSIONS
  The preoperative degeneration of the adjacent segment of the disc is a significant risk factor for ASD.
authors.affiliation: Department of Orthopaedics, Beijing Tiantan Hospital, Capital Medical University, Beijing, People's Republic of China.
authors.forename: Jia-Zhi
authors.initials: JZ
authors.lastname: Yan
authors.forename: Gui-Xing
authors.initials: GX
authors.lastname: Qiu
authors.forename: Zhi-Hong
authors.initials: ZH
authors.lastname: Wu
authors.forename: Xue-Song
authors.initials: XS
authors.lastname: Wang
authors.forename: Ze-Jun
authors.initials: ZJ
authors.lastname: Xing
mesh_terms: D000328:Adult; D019245:Compressive Strength; D003198:Computer Simulation; D055119:Elastic Modulus; D020342:Finite Element Analysis; D006801:Humans; D055959:Intervertebral Disc Degeneration / Q000209:etiology* / Q000503:physiopathology*; D008159:Lumbar Vertebrae / Q000503:physiopathology* / Q000601:surgery*; D008297:Male; D008954:Models, Biological; D013123:Spinal Fusion / Q000009:adverse effects*; D013314:Stress, Mechanical; D016896:Treatment Outcome