ROTATION OF THE CERVICAL SPINAL COLUMN - A COMPUTED-TOMOGRAPHY IN-VIVO STUDY

The functional anatomy of the spinal column has mainly been studied in the cadaver. The aim of our study was to determine in vivo the normal axial rotation of the cervical column using computed tomography (CT). Sixty subjects, divided into decades from 20 to 80 years of age were studied. The CT protocol comprised an axial cut at the level of the skull base (CO) and at each vertebral level in the neck, in the neutral position (with the nasal septum vertical) and during rotation of the head. To reduce the exposure to irradiation the subjects were divided into two groups: 40 were studied from C0 to the fifth cervical vertebra (C5) with unilateral rotation at C0 of 10 degrees, 20 degrees and 40 degrees (20 rotations to the left and 20 to the right), and 20 subjects were studied from CO to the first thoracic vertebra (T1) with a maximum rotation at C0 to left and right. The angular position of a vertebra was defined as the anteroposterior axis with reference in the neutral position to the axis of C0, and in rotation was related to its original axis. At each vertebral level the mean angle of rotation and its standard deviation were calculated (n=30) for the successive intermediate and maximum rotations at C0 level. The rotation of the cervical spine took place mainly at two levels: 58% between C1 and C2 and 24% between C3 and C6. The pairs of vertebrae C0/C1 and C2/C3 provided functional couples where the rotation was minimal. Rotation of the lower cervical spine occurred very early. The percentage of rotation with respect to C0 of each cervical vertebra was constant during the successive rotations. The neutral positions of the vertebrae below the atlas were variable. The findings on rotation to left and to right were comparable. This study determined in vivo the distribution of rotation at each vertebral level of the cervical spine during partial and maximum rotation of the skull base. It facilitates the application of CT to the examination of disorders affecting the rotation of the cervical spinal column.