title: Neck motion due to the halo-vest in prone and supine positions.
abstract: METHODS
  An in vitro biomechanical study of the effectiveness of halo-vest fixation.
  
  
  OBJECTIVE
  The objective was to evaluate motion of the injured cervical spine with normal halo-vest application and vest loose in the prone and supine positions.
  
  
  BACKGROUND
  Snaking motion of the neck is defined as rotation in opposing directions throughout the cervical spine. Previous clinical studies have suggested snaking neck motion due to the halo-vest may lead to inadequate healing or nonunion.
  
  
  METHODS
  The halo-vest was applied to a Human Model of the Neck, which consisted of a cervical spine specimen mounted to the torso of an anthropometric test dummy and carrying a surrogate head. The model was transitioned from prone, to upright, to supine with the halo-vest applied normally and with the vest loose. Average peak spinal motions were computed in the prone and supine positions and contrasted with the physiologic rotation range, obtained from the intact flexibility test, and statistically compared (P < 0.05) between normal halo-vest application and vest loose.
  
  
  RESULTS
  Snaking motion of the neck was observed in the prone and supine positions, consisting of extension at head/C1 and C1/2 and flexion at the inferior spinal levels. The intervertebral rotation peaks generally exceeded the physiologic range throughout the cervical spine due to the loose vest in the prone position. Significant increases in the extension peaks at head/C1 (16.9 degrees vs. 5.7 degrees) and flexion peaks at C4/5 (6.9 degrees vs. 3.6 degrees) and C7-T1 (5.2 degrees vs. 0.7 degrees) were observed in the prone position due to the loose vest, as compared to normal halo-vest application. Axial neck separation was consistently observed in the prone and supine positions.
  
  
  CONCLUSIONS
  The present results, which document snaking motion of the cervical spine due to the halo-vest, indicate that an inadequately fitting or loose vest may significantly diminish its immobilization capacity leading to delayed healing or nonunion.
authors.affiliation: Department of Orthopaedics and Rehabilitation, Biomechanics Research Laboratory, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA. paul.ivancic@yale.edu
authors.forename: Paul C
authors.initials: PC
authors.lastname: Ivancic
authors.forename: Connor J
authors.initials: CJ
authors.lastname: Telles
mesh_terms: D000369:Aged, 80 and over; D001696:Biomechanical Phenomena / Q000502:physiology; D002102:Cadaver; D002574:Cervical Vertebrae / Q000033:anatomy & histology / Q000502:physiology*; D016267:External Fixators / Q000592:standards*; D005260:Female; D005592:Fracture Fixation / Q000379:methods*; D019416:Head Movements / Q000502:physiology; D006801:Humans; D007593:Joint Instability / Q000209:etiology / Q000503:physiopathology / Q000628:therapy*; D008297:Male; D008953:Models, Anatomic; D011187:Posture / Q000502:physiology; D016684:Prone Position / Q000502:physiology; D016059:Range of Motion, Articular / Q000502:physiology*; D016103:Spinal Fractures / Q000503:physiopathology / Q000628:therapy*; D016683:Supine Position / Q000502:physiology; D016474:Weight-Bearing / Q000502:physiology; D021801:Zygapophyseal Joint / Q000033:anatomy & histology / Q000502:physiology