CERVICAL ZYGAPOPHYSEAL JOINTS - GEOMETRICAL PARAMETERS AND RELATIONSHIP TO CERVICAL KINEMATICS

The relationship was examined between the height and slope of the cerv ical zygapophyseal joints and the patterns of motion of the cervical v ertebrae. The height and orientation of the C-3-C-7 superior articular processes were measured in lateral radiographs of 40 normal subjects. The C-4-C-6 facets were oriented at approximately 40 degrees to the v ertical, while the Cg and C-7 facets were more steeply oriented. The h eights of the superior articular processes were found to increase at p rogressively lower vertebral levels. Contrary to published views, the slope of the superior articular facets has no bearing on the pattern o f motion of the cervical vertebrae. No relationship was found between slope of the facets and the location of the instantaneous axes of rota tion of the cervical vertebrae. In contrast the height of the articula r processes was perfectly related to the location of the axes of rotat ion. Articular height, but not slope, is a major determinant of the pa tterns of motions of the cervical vertebrae. This study provides data necessary to confirm or deny the putative roles of the cervical zygapo physeal joints in determining motion of the cervical spine in the sagi ttal plane.