3-DIMENSIONAL FLEXIBILITY CHARACTERISTICS OF THE HUMAN CERVICAL-SPINEIN-VIVO

Study Design. A test-retest design to establish the reliability of a n ew system capable of quantifying the load-displacement characteristics of the cervical spine. The study was primarily descriptive, but the d esign allowed comparisons between men and women as well as within-grou p comparisons among different cervical motions. Objectives. TO determi ne the flexibility of the entire cervical spine in vivo and to establi sh the reliability of a new system developed for this purpose. Summary of Background Data. The flexibility of the cervical spine has been st udied primarily in vitro by applying loads to isolated osteoligamentou s segments, Quantification of the mechanical characteristics of the ce rvical spine in vivo may provide insights to the effects of pathology and treatment interventions. In vivo flexibility measurements differ f rom those in vitro in that they involve the entire cervical spine comp osite, including the muscles, rather than isolated segments. Methods. Our method uses a 6 degrees of freedom mechanical linkage system align ed anatomically according to Grood and Suntay parameters and allows ma nual application of torque around each axis. We determined the range o f motion and flexibility of the cervical spine in a sample of young, h ealthy subjects (n = 20) for flexion, right lateral bending, and bilat eral axial rotation. Results. Acceptable test-retest reliability were found for range of motion and flexibility measurements performed sever al days apart. The general shape of the torque-angle curves was nonlin ear and biphasic An early, very flexible portion of the curve was defi ned as the neutral zone, and the less flexible, end portion of the cur ve was defined as the elastic zone. We found that men were less flexib le than women and that men could tolerate greater amounts of passively applied torques; All subjects showed significantly greater flexibilit y and less torque tolerance in axial rotation compared with those valu es in flexion and lateral bending. Possible anatomic explanations for these differences include the effect of muscle alignment and flexibili ty differences between synovial and fibrocartilaginous articulations. Conclusions, This study provides data regarding the in vivo flexibilit y of the human neck in young, healthy subjects and forms the basis for comparison in future studies that assess the effects of pathology and treatment, Men have lower flexibility than women, and axial rotation flexibility is significantly greater than that in lateral bending and flexion.