Healthy Adult Subaxial Cervical Spine Center Of Rotation:An In Vivo Kinematics Study

Objective:(1)To measure the 6-DOF data of the C3-C7 segment under flexion and extension and the position of the center of rotation.(2)Exploring the distribution characteristics of the center of rotation of the cervical spine of flexion and extension in normal people of different genders.By exploring the physiological characteristics of the cervical spine,the potential biomechanics of cervical degenerative diseases can be further understood,and parameters for cervical disc replacement prosthesis placement and prosthesis design can be provided.Methods:In order to explore the position of the cervical spine in body rotation center,15 healthy volunteers were recruited,including 7 males and 8 females,aged 23-41years(mean age 26.6 years),history of cervical spondylosis,history of cervical spine surgery,Neck discomfort and abnormal development.The dual fluoroscopic imaging system(DFIS)combined with CT/MRI was used to reconstruct the three-dimensional structure of the cervical spine.The images of the cervical spine were acquired by spiral CT scanning of the subject's cervical spine,and then the captured images of the cervical spine were imported into the three-dimensional modeling software.In Rhinoceros,a three-dimensional model of the cervical spine is reconstructed.Two simultaneous C-arms of the dual fluoroscopy system simultaneously photographed the subject's cervical neutral position,the maximum flexion position,and the maximum extension position.The acquired two-dimensional perspective of the cervical spine was compared with the above-mentioned three-dimensional model of cervical vertebrae using Rhinoceros software.Matching,in the C3-C7 cervical spine marker to establish three-dimensional coordinates,get the maximum cervical flexion,neutral position,the maximum extension position and the entire flexion and extension of the movement of the value,but also get the cervical vertebra in different states of the trajectory,and finally The obtained values were calculated by the linear fitting method to find the position of the rotation center of the vertebral body on the sagittal diameter of the vertebral body.Results:(1)The position distribution of the rotation center of the vertebral body between the lower cervical segment under physiological load: The rotation center of the C3/4 segment flexion and extension movement was located in front of the vertebral body of all subjects under physiological load.The center of rotation of the C4/5 segment flexion and extension was about 5.6 mm in front of the center of the vertebral body,and the center of rotation of the C5/6 segment flexion and extension was about 5.6 mm in front of the center of the vertebral body.The rotation of the C6/7segment flexion and extension motion was 4.4mm.The center is about 0.9mm in front of the center of the vertebral body.All subjects were divided into two groups according to gender: Male group: The rotation center of the C3/4 segment flexion and extension movement was approximately 4.1 mm in front of the center of the vertebral body,and the rotation center of the C4/5 segment flexion and extension movement was located in front of the center of the vertebral body approximately 5.4 The rotation center of the mm and C5/6 segmental flexion and extension motion is approximately7.0 mm in front of the center of the vertebral body.The rotation center of the C6/7segment flexion and extension motion is approximately 1.7 mm behind the center of the vertebral body.The female group: C3/4 segmental flexion and extension motion The center of rotation is about 4.7mm in front of the center of the vertebral body.The center of rotation of the C4/5 segment flexion and extension is about 5.8mm in front of the center of the vertebral body,and the center of rotation of the C5/6 segment of flexion and extension is about 4.4mm in front of the center of the vertebral body.The center of rotation of the C6/7 segment flexion and extension movement is approximately 0.3 mm behind the center of the vertebral body.The position of the C5/6 segment rotation center was compared between the male and female groups,and the female group was closer to the center of the vertebral body than the male group.The difference was statistically significant(P<0.05).The rotational center positions of the maximum flexion position and the maximum postoperative position were calculat-ed separately.There was no statistical difference in the position of the rotation center between the male and female groups in each segment.(2)Comparison of sagittal diameters of various segments of the lower cervical spine between different sexes: Male group: C3: 16.6mm,C4: 17.0mm,C5: 17.3mm,C6:18.0mm,C7: 18.6mm,female group: C3: 14.1 Mm,C4:14.3mm,C5:15.0mm,C6:15.9mm,C7:16.2mm.The sagittal diameter of the vertebral body in each segment between the male and female groups was statistically significant(P<0.05).Conlusion: In this experiment,in order to construct the instantaneous motion of the lower cervical spine under physiological loads of healthy adults,the 3D spatial data of different anatomic landmarks of the lower cervical spine were measured by two-dimensional and three-dimensional matching techniques,and the rotation was calculated by a linear fitting method.The position of the center,the physiological characteristics of normal human lower cervical flexion and extension activities,to provide a theoretical basis for placement and design of the prosthesis.