title: A biomechanical analysis of metastatic vertebral collapse of the thoracic spine: a sheep model study.
abstract: METHODS
  This is a biomechanical study using sheep thoracic spine to investigate the probability of mechanical failure of the thoracic spine with various sizes or locations of tumor metastasis.
  
  
  OBJECTIVE
  The objectives of this study were to investigate biomechanical effects of not only tumor sizes within the thoracic vertebral body but also its involvement of other spinal components on the probability of mechanical failures of the thoracic spine.
  
  
  BACKGROUND
  There have been no experimental studies concerning mechanical influences of destruction of costovertebral joint or posterior elements as well as vertebral body on the load-bearing capacity of the thoracic spine.
  
  
  METHODS
  Ninety-nine fresh sheep thoracic spine specimens with ribs were used (T7-T9, T10-T12). Within vertebral bodies of 39 specimens, only trabecular defects were created in different sizes. In other 48 specimens, not only vertebral body defects that were 40% to the cross-sectional area of the vertebral body but also additional destruction of costovertebral joint, pedicle, and facet joint were created. All specimens were subjected to destructive biomechanical testing.
  
  
  RESULTS
  The failure load decreased as the defect size in the vertebral body increased. A negative linear correlation was observed between the failure load and the size of vertebral body defect (r = 0.782). With 40% cross-sectional defect in the vertebral body, additional costovertebral joint destruction brought 25% reduction of the failure load, which was statistically significant.
  
  
  CONCLUSIONS
  The load-bearing capacity of metastasized vertebrae in the thoracic spine was proportionally decreased when the defect size in the vertebral body increased. Destruction of costovertebral joint significantly increased the probability of vertebral collapse.
authors.affiliation: Department of Orthopaedic Surgery, Hokkaido University Graduate School of Medicine, Sapporo, Japan.
authors.forename: Hibiki
authors.initials: H
authors.lastname: Ebihara
authors.forename: Manabu
authors.initials: M
authors.lastname: Ito
authors.forename: Kuniyoshi
authors.initials: K
authors.lastname: Abumi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Taneichi
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Kotani
authors.forename: Akio
authors.initials: A
authors.lastname: Minami
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Kaneda
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D007403:Intervertebral Disc / Q000000981:diagnostic imaging / Q000503:physiopathology; D008297:Male; D008954:Models, Biological; D009362:Neoplasm Metastasis / Q000503:physiopathology*; D011859:Radiography; D012272:Ribs / Q000503:physiopathology; D012307:Risk Factors; D012756:Sheep; D013314:Stress, Mechanical; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery; D016474:Weight-Bearing