title: Stabilizing properties of the halo apparatus.
abstract: METHODS
  A cadaveric cervical spine specimen fixed between a fiberglass torso and a plastic skull was used as a model to determine the effect of halo structural parameters on motion at a lesion simulated at C5-C6. In a second part, nine commercially available halo devices were compared.
  
  
  OBJECTIVE
  To define the contributions of the various components of the halo apparatus to reducing motion in an injured cervical spine and to compare the stability offered by a sample of commercially available halo devices. Controversy exists concerning the ability of the halo apparatus to stabilize the injured cervical spine.
  
  
  BACKGROUND
  The halo apparatus has been shown to be the most effective nonsurgical method for stabilizing the fractured spine. Nonetheless, several clinical studies have demonstrated that unacceptably large motions can occur at the injured spinal segment stabilized with a halo apparatus.
  
  
  METHODS
  Each cadaveric cervical spine was mounted onto a fiberglass torso and a rigid plastic skull was attached to the base of the occiput. A posterior ligamentous lesion was created between C5 and C6. The halo ring was fitted to the skull and a vest to the torso. Loads were applied to the skull in flexion, extension, and lateral bending, and relative angulation between C5 and C6 was measured with electroinclinometers. In the first part, the effect of parameters such as vest tightness, vest-thorax friction, vest deformation, and connecting bar rigidity on spinal angulation were measured using one vest. In the second part, the stability offered by each of nine commercially available halo devices was compared.
  
  
  RESULTS
  Increasing chest strap tightness and decreasing vest deformation reduced angulation at the spinal lesion. Once connecting bar joints were tightened to 25% of their recommended torque, increased tightening or adding additional bars had no effect on rigidity. Although specific vests permitted significantly greater motion in specific directions, no vest allowed greater angulation consistently in all loading planes.
  
  
  CONCLUSIONS
  Increasing vest tightness, decreasing the deformability of the vest, and ensuring a good fit can reduce motion in the fractured spine. Most commercially available halo vests provide similar mechanical stability to the injured cervical spine.
authors.affiliation: Department of Orthopaedic Surgery, University of Washington, Seattle, USA.
authors.forename: S K
authors.initials: SK
authors.lastname: Mirza
authors.forename: R R
authors.initials: RR
authors.lastname: Moquin
authors.forename: P A
authors.initials: PA
authors.lastname: Anderson
authors.forename: A F
authors.initials: AF
authors.lastname: Tencer
authors.forename: J
authors.initials: J
authors.lastname: Steinmann
authors.forename: D
authors.initials: D
authors.lastname: Varnau
mesh_terms: D001696:Biomechanical Phenomena; D002102:Cadaver; D002574:Cervical Vertebrae; D005592:Fracture Fixation / Q000379:methods*; D017276:Friction; D006801:Humans; D009989:Orthotic Devices; D013124:Spinal Injuries / Q000628:therapy*