In Vivo Study Of Coupled Motion Characteristics Of Cervical Spine In Healthy People

Objective This study investigated the in vivo characteristic motion patterns of the human cervical spine during a dynamic axial rotation,lateral bending and flexion-extension motion of the neck with physiological weight bearing.Specifically,the contribution of each motion segment to the whole three-dimensional range of motion during the dynamic axial rotation,lateral bending and flexion-extension motion were analyzed.Methods 16 asymptomatic volunteers(age 22.9 years on average,ranging from 22 to 29)were recruited to our study,any cervical spine disorder history,pain or other uncomfortable symptoms and malformations been 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: neutral position,maximal left and right twisting,maximal left and right lateral bending,maximal flexion and extension;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,the change of position and angle of each cephalad vertebrae relative to the cauddal one was calculated before and after the axial rotation,before and after lateral bending,also flexion and extension.Results 1.(1)In the axial rotation of the cervical spine,the contribution of C1/2 accounted for the most(approximately 77 percent)of the whole angle of C1 with respect to C7.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 dimonstrated 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 C5/6.2.(1)In the lateral bending of the cervical spine,the contribution of C1/2,C2/3,C3/4,C4/5,C5/6 and C6/7 were calculated respectively.Among these segments,C2/3 accounte for the minimal of the whole angle of C1 with respect to C7.(2)In cervical lateral bending,C1/2 dimonstrated a coupled axial rotaton opposite to the lateral bending direction,while each segment of C2-7 demonstrated coupled lateral bending towards the same side of the axial rotation.Among these segments the coupled axial rotation angle of C2/3 was smaller than others,and the angle of C3/4 was the most.3.(1)In the flexion-extension of the cervical spine,the contribution of each segments of C1-7 were calculated respectively.Among these segments,C4/5、C5/6 accounted for the maximum of the whole angle of C1 with respect to C7,following C3/4,C2/3 accounted for the minimal.(2)In cervical flexion and extension,all the segments were not shown to have definite coupling rotation and coupling lateral bending.Conclusions This study investigated the cervical coupling behavior using the noninvasive 2D-3D matching technique and obtained the three-dimensional motion data at each cervical spinal segment for the first time.These findings will help to improve the understanding on physiological cervical spine movement and potential biomechanical mechanism of cervical spondylosis.Also,Our data may provide useful reference for the prosthesis design.