Sagittal kinematics of the cervical spine--how constant are the motor axes?

The aim of this study was to establish whether or not the axes of cervical spine movement in the sagittal plane are constant (an impression conveyed by the literature). Based on 60 functional radiographs (of which 24 showed degenerative discopathy or atlas subluxations), the axes of seven motor segments (C1-D1) were determined geometrically. The axes of the segments C5/C6 proved to scatter least; the further the distance of a segment is to the latter, the larger the tendency of scattering appears. Hence, the axes are neither constant in time nor in location and thus only convey the momentary kinematic situation of the cervical spine. Clearly pathologic axis positions could not be found, except in the case of an extreme atlas subluxation.