Cervical zygapophyseal joints: geometrical parameters and relationship to cervical kinematics.

The relationship was examined between the height and slope of the cervical zygapophyseal joints and the patterns of motion of the cervical vertebrae. The height and orientation of the C3C7 superior articular processes were measured in lateral radiographs of 40 normal subjects. The C4-C6 facets were oriented at approximately 40° to the vertical, while the C3 and C7 facets were more steeply oriented. The heights of the superior articular processes were found to increase at progressively lower vertebral levels. Contrary to published views, the slope of the superior articular facets has no bearing on the pattern of motion of the cervical vertebrae. No relationship was found between slope of the facets and the location of the instantaneous axes of rotation of the cervical vertebrae. In contrast the height of the articular processes was perfectly related to the location of the axes of rotation. Articular height, but not slope, is a major determinant of the patterns of motions of the cervical vertebrae. This study provides data necessary to confirm or deny the putative roles of the cervical zygapophyseal joints in determining motion of the cervical spine in the sagittal plane.