title: Predicting multiplanar cervical spine injury due to head-turned rear impacts using IV-NIC.
abstract: OBJECTIVE
  Intervertebral Neck Injury Criterion (IV-NIC) hypothesizes that dynamic three-dimensional intervertebral motion beyond physiological limit may cause multiplanar soft-tissue injury. Present goals, using biofidelic whole human cervical spine model with muscle force replication and surrogate head in head-turned rear impacts, were to: (1) correlate IV-NIC with multiplanar injury, (2) determine IV-NIC injury threshold at each intervertebral level, and (3) determine time and mode of dynamic intervertebral motion that caused injury.
  
  
  METHODS
  Impacts were simulated at 3.5, 5, 6.5, and 8 g horizontal accelerations of T1 vertebra (n = 6; average age: 80.2 years; four male, two female donors). IV-NIC was defined at each intervertebral level and in each motion plane as dynamic intervertebral rotation divided by physiological limit. Three-plane pre- and post-impact flexibility testing measured soft-tissue injury; that is significant increase in neutral zone (NZ) or range of motion (RoM) at any intervertebral level, above baseline. IV-NIC injury threshold was average IV-NIC peak at injury onset.
  
  
  RESULTS
  IV-NIC extension peaks correlated best with multiplanar injuries (P < 0.001): extension RoM (R = 0.55) and NZ (R = 0.42), total axial rotation RoM (R = 0.42) and NZ (R = 0.41), and total lateral bending NZ (R = 0.39). IV-NIC injury thresholds ranged between 1.1 at C0-C1 and C3-C4 to 2.9 at C7-T1. IV-NIC injury threshold times were attained between 83.4 and 150.1 ms following impact.
  
  
  CONCLUSIONS
  Correlation between IV-NIC and multiplanar injuries demonstrated that three-plane intervertebral instability was primarily caused by dynamic extension beyond the physiological limit during head-turned rear impacts.
authors.affiliation: Biomechanics Research Laboratory, Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, Connecticut, USA. paul.ivancic@yale.edu
authors.forename: Paul C
authors.initials: PC
authors.lastname: Ivancic
authors.forename: Manohar M
authors.initials: MM
authors.lastname: Panjabi
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Tominaga
authors.forename: George F
authors.initials: GF
authors.lastname: Malcolmson
mesh_terms: D000054:Acceleration; D000063:Accidents, Traffic; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D002102:Cadaver; D002574:Cervical Vertebrae / Q000293:injuries*; D005260:Female; D006801:Humans; D007403:Intervertebral Disc / Q000293:injuries*; D008297:Male; D008954:Models, Biological; D019838:Neck Injuries; D016059:Range of Motion, Articular; D012399:Rotation; D017695:Soft Tissue Injuries