title: Head-turned rear impact causing dynamic cervical intervertebral foramen narrowing: implications for ganglion and nerve root injury.
abstract: OBJECTIVE
  A rotated head posture at the time of vehicular rear impact has been correlated with a higher incidence and greater severity of chronic radicular symptoms than accidents occurring with the occupant facing forward. No studies have been conducted to quantify the dynamic changes in foramen dimensions during head-turned rear-impact collisions. The objectives of this study were to quantify the changes in foraminal width, height, and area during head-turned rear-impact collisions and to determine if dynamic narrowing causes potential cervical nerve root or ganglion impingement.
  
  
  METHODS
  The authors subjected a whole cervical spine model with muscle force replication and a surrogate head to simulated head-turned rear impacts of 3.5, 5, 6.5, and 8 G following a noninjurious 2-G baseline acceleration. Continuous dynamic foraminal width, height, and area narrowing were recorded, and peaks were determined during each impact; these data were then statistically compared with those obtained at baseline. The authors observed significant increases (p < 0.05) in mean peak foraminal width narrowing values greater than baseline values, of up to 1.8 mm in the left C5-6 foramen at 8 G. At the right C2-3 foramen, the mean peak dynamic foraminal height was significantly narrower than baseline when subjected to rear-impacts of 5 and 6.5 G, but no significant increases in foraminal area were observed. Analysis of the results indicated that the greatest potential for cervical ganglion compression injury existed at C5-6 and C6-7. Greater potential for ganglion compression injury existed at C3-4 and C4-5 during head-turned rear impact than during head-forward rear impact.
  
  
  CONCLUSIONS
  Extrapolation of present results indicated potential ganglion compression in patients with a non-stenotic foramen at C5-6 and C6-7; in patients with a stenotic foramen the injury risk greatly increases and spreads to include the C3-4 through C6-7 as well as C4-5 through C6-7 nerve roots.
authors.affiliation: Biomechanics Research Laboratory, Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, Connecticut 06520-8071, USA.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Tominaga
authors.forename: Travis G
authors.initials: TG
authors.lastname: Maak
authors.forename: Paul C
authors.initials: PC
authors.lastname: Ivancic
authors.forename: Manohar M
authors.initials: MM
authors.lastname: Panjabi
authors.forename: Bryan W
authors.initials: BW
authors.lastname: Cunningham
mesh_terms: D000054:Acceleration; D000063:Accidents, Traffic; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D002574:Cervical Vertebrae / Q000293:injuries* / Q000503:physiopathology; D002908:Chronic Disease; D005260:Female; D019416:Head Movements / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008432:Mathematical Computing; D008953:Models, Anatomic; D009408:Nerve Compression Syndromes / Q000209:etiology / Q000503:physiopathology; D009949:Orientation / Q000502:physiology*; D011843:Radiculopathy / Q000209:etiology / Q000503:physiopathology; D011856:Radiographic Image Enhancement; D013126:Spinal Nerve Roots / Q000293:injuries / Q000503:physiopathology; D013130:Spinal Stenosis / Q000503:physiopathology*; D017783:Superior Cervical Ganglion / Q000293:injuries / Q000503:physiopathology; D014911:Whiplash Injuries / Q000503:physiopathology*