Abstract: Objective To determine the three dimensional motion data of each segment of cervical vertebrae and analyze the characteristics of the intervertebral coupled motion during cervical axial rotation under physiological weight bearing. Methods A total of 16 healthy volunteers (ranging from 22 to 29, median age, 23 years) were recruited to our study. Any cervical spine disorder history, pain or other discomfort and malformations were excluded so as to avoid abnormal neck motion. These subjects underwent CT scans of their cervical segments in a supine position, and 3D models of C1-C7 were constructed. Next, each subject was asked to sit up straight and was positioned in the following sequence: maximal left and right twisting, while double oblique images by DFIS were taken simultaneously at each of the positions. Then, the CT models were matched to the osseous outlines of the images from the two oblique views to quantify the position of cervical vertebraes in 3D at each position. Through local coordinate systems at the center of vertebral bodies, changes of position and angle of each cephalad vertebrae relative to the cauddal one were calculated before and after the axial rotation. Results (1) In the axial rotation of the cervical spine, the contribution of C1/2 accounted for the most of the total cervical rotation range. For the lower levels, axial rotation was found to be maximal at C3/4 and C5/6, minimal at C2/3. (2) In cervical axial motion, C1/2 demonstrated a coupled lateral bending opposite to the axial rotation direction, while each segment of C2- 7 demonstrated coupled lateral bending towards the same side of the axial rotation. Among these segments the lateral bending angle of C2/3 was smaller than angles of C3/4, C4/5 and C5/6. Conclusion This study investigated the cervical coupling behavior using the noninvasive 2D-3D matching technique and obtained the motion data at each cervical spinal segment. These findings will help to improve the understanding on physiological cervical spine movement and potential biomechanical mechanism and treatment of cervical spondylosis. Also our data may provide useful reference for the prosthesis design.

Key words: cervical vertebrae, biomechanics, 2D-3D matching, coupled motion, spinal surgery