In vivo flexion/extension of the normal cervical spine.

Twenty-two women (age range 25-49 years, average 30.9 years) and twenty-two men (age range 23-42 years, average 31.6 years), all healthy and asymptomatic, underwent passive flexion/extension examinations of the cervical spine. Functional x-rays were taken and analyzed using a computer-assisted method that quantified intervertebral rotations, translations, and locations of the centers of rotation for each level C1-C2-C6-C7. The aim of the study was to establish values for these parameters for a normal population as related to age and gender. In the process, a statistically significant difference was found in the average value of rotation between male and female groups at the C5-C6 level. A new parameter, the ratio between translation and rotation, was also established and may prove useful for clinical diagnoses. This parameter has a smaller error associated with it than do pure translations and may aid the clinician by helping to account for the large variation in rotatory ranges of motion within the population. This translation/rotation ratio indicated highly significant differences in the lower segments of the cervical spine between gender groups.