title: Acute thoracolumbar burst fractures: a new view of loading mechanisms.
abstract: METHODS
  An in vitro investigation of loading mechanisms in acute thoracolumbar burst fractures.
  
  
  OBJECTIVE
  To assess the validity of the authors' hypothesis that anterior shear forces transmitted by the facet joints are responsible for causing the severe canal compromise associated with acute thoracolumbar burst fractures.
  
  
  BACKGROUND
  Thoracolumbar burst fractures created in the laboratory rarely match the severity of clinical cases. To date, no studies have examined in great detail the role of facet joint loading in the burst-fracture mechanism. An incomplete understanding of loading mechanisms may contribute to the controversies regarding management.
  
  
  METHODS
  Nine human cadaveric motion segments were instrumented with strain gages and subjected to axial compression or axial impact coupled with an extension moment. Failure loads, strain information, and radiographs were collected.
  
  
  RESULTS
  Fracture patterns characteristic of acute thoracolumbar burst fractures were observed in the three specimens tested with an extension moment. In this group, high strains were also recorded at the bases of the pedicles, indicating a probable site of fracture initiation. Specimens tested in a neutral orientation experienced crush fractures without an increase in interpedicular distance. Strain patterns were more uniform in this group.
  
  
  CONCLUSIONS
  The severity and clinical relevance of the injuries sustained by the specimens tested in extension suggest that facet joint loading plays a critical role in the acute thoracolumbar burst-fracture loading mechanism. Fracture patterns and strain concentrations are in agreement with clinical observations as well as past experimental studies.
authors.affiliation: Department of Mechanical and Aerospace Engineering, Rutgers University, Piscataway, New Jersey, USA. langrana@caip.rutgers.edu
authors.forename: N A
authors.initials: NA
authors.lastname: Langrana
authors.forename: R D
authors.initials: RD
authors.lastname: Harten RD
authors.forename: D C
authors.initials: DC
authors.lastname: Lin
authors.forename: M F
authors.initials: MF
authors.lastname: Reiter
authors.forename: C K
authors.initials: CK
authors.lastname: Lee
mesh_terms: D000208:Acute Disease; D000368:Aged; D001696:Biomechanical Phenomena; D002102:Cadaver; D020342:Finite Element Analysis; D006801:Humans; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000293:injuries* / Q000503:physiopathology; D008875:Middle Aged; D008954:Models, Biological; D009038:Motion; D011859:Radiography; D015203:Reproducibility of Results; D016103:Spinal Fractures / Q000000981:diagnostic imaging / Q000209:etiology* / Q000503:physiopathology*; D013314:Stress, Mechanical; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging / Q000293:injuries* / Q000503:physiopathology