title: The influence of facet joint orientation and tropism on the stress at the adjacent segment after lumbar fusion surgery: a biomechanical analysis.
abstract: BACKGROUND
  Facet joint orientation and tropism influence the biomechanics of the corresponding segment. Therefore, the sagittal orientation or tropism of the facet joint adjacent to the fusion segment seems a potential risk factor for adjacent segment degeneration. However, there have been no biomechanical studies regarding this issue.
  
  
  OBJECTIVE
  To investigate the association between adjacent facet orientation and facet tropism and stress in adjacent disc/facet joints using finite element (FE) analysis.
  
  
  METHODS
  An FE analysis.
  
  
  METHODS
  Four intact (F50, F55, F60, and FT [facet tropism]) and matched L3-L4 fusion (F50, F55, F60, and FT fusion) models with different facet joint orientation (50°, 55°, 60° relative to the coronal plane, and facet tropism, respectively) at both L2-L3 facet joints were simulated. In each model, intradiscal pressures and facet contact force at the L2-L3 segment were investigated under pure moments and anterior shear force.
  
  
  RESULTS
  Compared with the matched-intact model, the F60 fusion model yielded the highest and largest percentage increase of intradiscal pressure at the L2-L3 segment under flexion, torsion moment, and anterior shear force among the F50, F55, and F60 fusion models. F60 fusion model also demonstrated the largest facet contact force under torsion moment among the F50, F55, and F60 fusion models. In all conditions tested, the FT fusion model demonstrated the highest intradiscal pressure and facet contact force of all the models.
  
  
  CONCLUSIONS
  Facet joint orientation and tropism at the adjacent segment influences the overstress of the adjacent segment, especially under the clinical circumstance of increased anterior shear force.
authors.affiliation: Spine Center and Department of Orthopaedic Surgery, Seoul National University College of Medicine and Seoul National University Bundang Hospital, 166 Gumiro, Bundang-gu, Sungnam, 463-707, Republic of Korea.
authors.forename: Ho-Joong
authors.initials: HJ
authors.lastname: Kim
authors.affiliation: Department of Mechanical Engineering, Yonsei University, 134 Shinchon-dong, Seodaemun-gu, Seoul, Republic of Korea.
authors.forename: Kyoung-Tak
authors.initials: KT
authors.lastname: Kang
authors.affiliation: Department of Mechanical Engineering, Yonsei University, 134 Shinchon-dong, Seodaemun-gu, Seoul, Republic of Korea.
authors.forename: Juhyun
authors.initials: J
authors.lastname: Son
authors.affiliation: Department of Orthopaedic Surgery, Seoul National University College of Medicine and Seoul National University Hospital, 101 Daehangno, Jongno-gu, Seoul, 110-744, Republic of Korea.
authors.forename: Choon-Ki
authors.initials: CK
authors.lastname: Lee
authors.affiliation: Department of Orthopaedic Surgery, Seoul National University College of Medicine and Seoul National University Hospital, 101 Daehangno, Jongno-gu, Seoul, 110-744, Republic of Korea.
authors.forename: Bong-Soon
authors.initials: BS
authors.lastname: Chang
authors.affiliation: Spine Center and Department of Orthopaedic Surgery, Seoul National University College of Medicine and Seoul National University Bundang Hospital, 166 Gumiro, Bundang-gu, Sungnam, 463-707, Republic of Korea. Electronic address: highcervical@gmail.com.
authors.forename: Jin S
authors.initials: JS
authors.lastname: Yeom
mesh_terms: D001696:Biomechanical Phenomena; D020342:Finite Element Analysis; D006801:Humans; D007403:Intervertebral Disc / Q000503:physiopathology*; D008159:Lumbar Vertebrae / Q000503:physiopathology* / Q000601:surgery; D008297:Male; D011312:Pressure; D013123:Spinal Fusion; D013312:Stress, Physiological; D018523:Tropism; D021801:Zygapophyseal Joint / Q000503:physiopathology*
keywords: Adjacent segment degeneration; Anterior shear force; Facet orientation; Facet tropism; Finite element analysis; Lumbar fusion