Mechanical properties of the human cervical spine as shown by three-dimensional load-displacement curves

Study Design. The mechanical properties of multilevel human cervical spines were investigated by applying pure rotational moments to each specimen and measuring multidirectional intervertebral motions. Objectives. To document intervertebral main and coupled motions of the cervical spine in the form of load-displacement curves. Summary of Background Data. Although a number of in vivo and in vitro studies have attempted to delineate normal movement patterns of the cervical spine, none has explored the complexity of the whole cervical spine as a three-dimensional structure. Methods. Sixteen human cadaveric specimens (COC7) were used for this study. Pure rotational moments of flexion- extension, bilateral axial torque, and bilateral lateral bending were applied using a specially designed loading fixture, The resulting intervertebral motions were recorded using stereophotogrammetry and depicted as a series of load- displacement curves. Results. The resulting load-displacement curves were found to be nonlinear, and both rotation and translation motions were coupled with main motions. With flexion-extension moment loading, the greatest degree of flexion occurred at C1-C2 (12.3degrees), whereas the greatest degree of extension was observed at C0-C1 (20.2degrees). With axial moment loading, rotation at C1-C2 was the largest recorded (56.7degrees). With lateral bending moments, the average range of motion for all vertebral levels was 7.9degrees. Conclusions. The findings of the present study are relevant to the clinical practice of examining motions of the cervical spine in three dimensions and to the understanding of spinal trauma and degenerative diseases.