Three-dimensional motion analysis of the cervical spine with special reference to the axial rotation.

The purpose of this study is to obtain basic data on the rotational motion of the cervical spine. Twenty normal men aged 25 to 31 years were investigated. Biplanar roentgenograms of the neck with the head held in neutral and maximally rotated positions were taken in a reference frame. Three sets of x-ray films were measured using a three-dimensional analysis system composed of a digitizer and a personal computer. Total axial rotation was 105 degrees on an average between the occiput and the C7 vertebra. Seventy percent of the total axial rotation occurred between the occiput and the C2 vertebra. Each motion segment between the C2 and C7 vertebrae showed from 4 degrees to 8 degrees rotation on an average. When the head was rotated, lateral bending occurred by coupling in the same direction as rotation at each segment below the C3-C4 level, and in the opposite direction above the C2-C3 level. At the same time, flexion took place by coupling at each segment below the C5-C6 level, and extension above the C4-C5 level.