title: An exploratory study of loading and morphometric factors associated with specific failure modes in fatigue testing of lumbar motion segments.
abstract: BACKGROUND
  There is currently little information regarding factors associated with specific modes of motion segment failure using a fatigue failure model.
  
  
  METHODS
  Thirty-six human lumbar motion segments were fatigue tested using spinal compressive and shear loads that simulated lifting a 9 kg weight in three torso flexion angles (0 degrees, 22.5 degrees, and 45 degrees). Twenty-five segments failed via fatigue prior to the 10,000 cycle maximum. These specimens were visually inspected and dissected so that the mode(s) of failure could be determined. Failure modes included endplate fractures (classified into nine varieties), vertebral body fractures, and/or zygapophysial joint disruption. Logistic regression analyses were performed to determine whether certain morphometric variables, amount of motion segment flexion, disk degeneration scores, and/or loading characteristics were associated with the occurrence of specific failure modes.
  
  
  RESULTS
  Results indicated that stellate endplate fractures were associated with increased posterior shear forces (P < 0.05) and less degenerated discs (P < 0.01). Fractures running laterally across the endplate were associated with motion segments having larger volumes (P < 0.01). Endplate depression was more common in smaller specimens (P < 0.01), as well as those experiencing increased posterior shear force (P < 0.05). Zygapophysial joint damage was more likely to occur in a neutral posture (P < 0.01).
  
  
  CONCLUSIONS
  These results suggest that prediction of failure modes (e.g., specific endplate fracture patterns) may be possible (at least for older specimens) given knowledge of the spinal loads along with certain characteristics of the lumbar spine.
authors.affiliation: National Institute for Occupational Safety and Health, Mining Injury Prevention Branch, P.O. Box 18070, Pittsburgh, PA 15236-0070, USA. sgallagher@cdc.gov
authors.forename: Sean
authors.initials: S
authors.lastname: Gallagher
authors.forename: William S
authors.initials: WS
authors.lastname: Marras
authors.forename: Alan S
authors.initials: AS
authors.lastname: Litsky
authors.forename: Deborah
authors.initials: D
authors.lastname: Burr
mesh_terms: D000369:Aged, 80 and over; D002102:Cadaver; D019245:Compressive Strength; D006801:Humans; D066298:In Vitro Techniques; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D009068:Movement; D011859:Radiography; D033081:Shear Strength; D016103:Spinal Fractures / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D016474:Weight-Bearing