Cervical spine motion in the sagittal plane. II. Position of segmental averaged instantaneous centers of rotation--a cineradiographic study.

Anteflexion and retroflexion movements of the cervical spine were recorded cineradiographically during three measuring sessions to determine reproducibility as well as intraindividual and interindividual variability of segmental instantaneous centers of rotation (recorded as "averaged" and "standard"). Segmental averaged instantaneous centers of rotation were based on data obtained from all frames of the cineradiographic film by the use of the average pentagon and moving average method. Only the first and last frame were used to construct the segmental standard instantaneous centers of rotation. Contrary to segmental range of motion, a parameter of quantity of motion, the position of the averaged instantaneous centers of rotation (better than the standard), a parameter of quality of movement, shows a variability of such low extent that it seems feasible to use it to diagnose abnormal mobility or in assessing therapy in the neck region.