Rotation of the cervical spine. A CT study in normal subjects.

A computed tomography (CT) study of rotation of the cervical spine was undertaken in normal subjects aged 20 to 26 years. Section scans through the neck were made with the head in maximal rotation to the right or the left. Occiput, cervical spine, and first thoracic vertebra, thus, were depicted in different degrees of rotation with respect to the sagittal plane. These differences indicated the maximal degree of rotation in each of the eight segments between occiput and thoracic spine. Mean values for these segments were 1.0 degree, 40.5 degrees, 3.0 degrees, 6.5 degrees, 6.8 degrees, 6.9 degrees, 5.4 degrees and 2.1 degrees, respectively. Measurement error proved to be relatively small. By means of CT sections in the plane of the intervertebral joints (in three subjects in midposition, in one subject in maximal rotation of the head to one side) an axis of rotation could be constructed from the anatomic shape of the uncovertebral joints. The theory of Hall that the unciform processes are essential for rotation is confirmed and further elaborated.