title: The fracture risk of adjacent vertebrae is increased by the changed loading direction after a wedge fracture.
abstract: METHODS
  In vitro biomechanical study.
  
  
  OBJECTIVE
  To measure the effect that off-axis vertebral loading has on the stiffness and failure load of vertebrae.
  
  
  BACKGROUND
  Adjacent level vertebral fractures not only are common in patients who received a vertebroplasty treatment but also occur in patients with conservatively treated wedge fractures. The wedge-like deformity, which is present in both groups, changes the spinal alignment. The load of vertebrae adjacent to the fractured vertebra will change from perpendicular to the endplate to a more shearing, off-axis, load. This change may induce a higher fracture risk for vertebrae adjacent to wedge-like deformed vertebrae.
  
  
  METHODS
  Twenty vertebrae, harvested from one osteopenic cadaver spine and three osteoporotic cadaver spines, were loaded until failure. The vertebrae were loaded either perpendicular to the upper endplate, representing vertebrae in a spine without wedge fractures (0° group, n = 10), or at an angle of 20°, representing vertebrae adjacent to a wedge fracture (20° groups, n = 10). Vertebral failure load and stiffness were the most important outcome measures.
  
  
  RESULTS
  The failure load was significantly higher (P 5 0.028) when tested at 0° (2854 N, SD 5 622 N), compared with vertebrae tested at 20° (2162 N, SD 5 670 N). Vertebrae were also significantly stiffer (P, 0.001) when tested at 0° (4017 N/mm, SD 5 970 N/mm) than those tested at 20° (2478 N/mm, SD 5 453 N/mm).
  
  
  CONCLUSIONS
  The failure load of osteopenic/osteoporotic vertebrae was 24% lower under off-axis loads (20°) than under axial loads (0°). This study may lead to a better understanding of the etiology of adjacent vertebral fractures after wedge-like deformities and demonstrates the importance of height reconstruction of wedge fractures in order to normalize the loading conditions on adjacent vertebrae.
authors.affiliation: Orthopaedic Research Laboratory, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
authors.forename: René
authors.initials: R
authors.lastname: Aquarius
authors.forename: Jasper
authors.initials: J
authors.lastname: Homminga
authors.forename: Nico
authors.initials: N
authors.lastname: Verdonschot
authors.forename: Esther
authors.initials: E
authors.lastname: Tanck
mesh_terms: D000369:Aged, 80 and over; D001851:Bone Diseases, Metabolic / Q000503:physiopathology; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000503:physiopathology* / Q000601:surgery; D008297:Male; D010024:Osteoporosis / Q000503:physiopathology; D012307:Risk Factors; D016103:Spinal Fractures / Q000209:etiology / Q000503:physiopathology*; D013314:Stress, Mechanical; D013904:Thoracic Vertebrae / Q000503:physiopathology* / Q000601:surgery; D054854:Vertebroplasty; D016474:Weight-Bearing / Q000502:physiology*