Neck Motion Due to the Halo-Vest in Prone and Supine Positions

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. The objectives of this study were to evaluate motion of the injured cervical spine with normal halo-vest application and vest loose in the prone and supine positions. 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. 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° vs. 5.7°) and flexion peaks at C4/5 (6.9° vs. 3.6°) and C7/T1 (5.2° vs. 0.7°) 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. 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.