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Stabilizing Properties of the Halo Apparatus

Mirza, Sohail K., MD*; Moquin, Ross R., MD; Anderson, Paul A., MD; Tencer, Allan F., PhD*; Steinmann, John, DO§; Varnau, David, CPO

Biomechanics
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Study Design. 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.

Objectives. 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.

Summary of Background Data. 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.

From the *Department of Orthopaedic Surgery, University of Washington, Seattle, †the Department of Neurosurgery, National Naval Medical Center, Bethesda, Maryland, ‡Orthopaedics International, Seattle, §San Bernardino County Medical Center, San Bernardino, California, and ∥Center for Prosthetics Orthotics, Inc., Seattle, Washington.

Supported in part by the Department of Orthopaedic Surgery, University of Washington and by a grant from ACE Medical Co., Los Angeles, California. Halo devices were donated from the respective manufacturers.

The opinions expressed are those of the authors and do not reflect the opinion of the Department of the Navy.

Acknowledgment date: December 27, 1995.

First revision date: May 16, 1996.

Acceptance date: July 7, 1996.

Device status category: 9.

Address reprint requests to: Allan F. Tencer, PhD; Department of Orthopaedic Surgery; Box 359798; Harborview Medical Center; 325 Ninth Ave; Seattle, WA, 98104

© Lippincott-Raven Publishers.