Forces in the halo-vest apparatus.

A previous study by Koch and Nickel (1978) determined the changes in the distraction forces in the halo-vest during different activities. The present study determined the variations of forces in different directions between the halo and the vest also during different activities. Clip-on strain gauges were used to measure the strains in the bars, while an on-line computer system was used to compute the forces. Anterior-posterior forces were found to be comparable with vertical ones. These forces and the changes during a particular activity were caused by gravity forces of the head in activities involving a change in attitude; and vest distortion from changes in body shape, direct pushing from the lower abdomen, the arms and shoulders, or from supporting surfaces. Activities producing the highest force changes included bending forwards from a seated position and reaching over sideways while lying. Medial-lateral forces were small in comparison with vertical and anterior-posterior forces. Implications of the study were that pin-skull forces were multidirectional, and that certain improvements in design could be effected by accounting for the factors causing high forces and consequently cervical motion.