Forces and motions across the neck in patients treated with halo-vest.

A prospective study of the sagittal plane motion of the cervical spine, stabilized with a halo-vest was performed in 31 consecutive patients with unstable cervical spine injuries. Motion was measured in lateral radiograms taken with the patient in different positions and while performing various exercises. The extreme angle in extension and flexion in each motion segment, in any of the exercises, was measured and the sum of this maximal motion in each segment, between occiput and C6, was noted (maximal cervical motion). Distraction-compression forces across the neck were studied simultaneously with the motion study in the last 20 patients of the series. Strain gauges were mounted on the two vertical rods of the halo-vest and the forces were correlated to the motion of the spine. We found a mean maximal cervical motion of 51 degrees (about 70% of the normal motion). The halo-vest restricted the motion the most below C2 and the least above C2. In the supine position, all patients had a distraction force across the neck (mean: 51 N) that decreased in some exercises (eg, sitting, standing) and increased in others (eg, arm lifting, shoulder shrugging). Both the motion and the force varied widely between different types of exercises. There was a maximal variation of 175 N between the exercises. A positive correlation was found (r = 0.8) between the distraction force in the supine position and the maximal cervical motion. No significant differences of motion in the cervical spine were found between the rehabilitation exercises and common activities of daily living.