title: Effect of rotated head posture on dynamic vertebral artery elongation during simulated rear impact.
abstract: BACKGROUND
  Elongation-induced vertebral artery injury has been hypothesized to occur during non-physiological coupled axial rotation and extension of head. No studies have quantified dynamic vertebral artery elongation during head-turned rear impacts. Therefore, we evaluated effect of rotated head posture vs. forward head posture at the time of impact on dynamic vertebral artery elongation during simulated rear impacts.
  
  
  METHODS
  A whole cervical spine model with surrogate head and muscle force replication underwent either simulated head-turned (n = 6) or head-forward (n = 6) rear impacts of 3.5, 5, 6.5 and 8 g. Continuous dynamic vertebral artery elongation was recorded using custom transducer and compared to physiological values obtained during intact flexibility testing.
  
  
  RESULTS
  Average (SD) peak dynamic vertebral artery elongation of up to 30.5 (2.6) mm during head-turned rear-impact significantly exceeded (P < 0.05) the physiological beginning at 5 g. Highest peak elongation of 5.8 (2.1) mm during head-forward rear impact did not exceed physiological limit. Head-turned rear impact caused earlier occurrence of average peak vertebral artery elongation, 84.5 (4.2) ms vs. 161.0 (43.8) ms, and higher average peak vertebral artery elongation rate, 1336.7 (74.5) mm/s vs. 211.5 (97.4) mm/s, as compared to head-forward rear impact.
  
  
  CONCLUSIONS
  Elongation-induced vertebral artery injury is more likely to occur in those with rotated head posture at the time of rear impact, as compared to head-forward.
authors.affiliation: Biomechanics Research Laboratory, Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, 333 Cedar St., P.O. Box 208071, New Haven, CT 06520-8071, USA.
authors.forename: Paul C
authors.initials: PC
authors.lastname: Ivancic
authors.forename: Shigeki
authors.initials: S
authors.lastname: Ito
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Tominaga
authors.forename: Erik J
authors.initials: EJ
authors.lastname: Carlson
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Rubin
authors.forename: Manohar M
authors.initials: MM
authors.lastname: Panjabi
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002102:Cadaver; D002574:Cervical Vertebrae / Q000503:physiopathology*; D004548:Elasticity; D019416:Head Movements; D006801:Humans; D066298:In Vitro Techniques; D009119:Muscle Contraction; D009334:Neck Muscles / Q000503:physiopathology*; D011187:Posture; D012399:Rotation; D013314:Stress, Mechanical; D014711:Vertebral Artery / Q000293:injuries* / Q000503:physiopathology*; D014911:Whiplash Injuries / Q000503:physiopathology*