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Objective: Using the CT three-dimensional reconstruction to measure the activity degree of atlanto-occipital joint and the atlantoaxial joint in different directions and its coupling movement in healthy volunteers, and three dimensional motion range of the maximum rotation position of the upper cervical spine of cervical spondylosis patients, and to analyze the differences, verifing the reliability of the method at the meantime., Methods: From January 2014 to June 2015, 20 healthy adult subjects(healthy adult group), and 26 patients with cervieal spondylosis(cervical spondylosis group) were selected. In healthy adult group, there were 11 males and 9 females, aged from 22 to 26 years old with an average of (24.0±1.2) years, and in cervical spondylosis group, there were 24 males and 2 females, aged from 36 to 72 years old with an average of (52.8±8.6) years. Healthy adults underwent CT examination in neutral position, maximum right rotation, maximum right lateral bending, maximum flexion and extention, and cervical spondylosis patients underwent CT examination in neutral position, maximum right rotation. Then the software Mimics was used to reconstruct occiput (Oc), atlas(C1) and axial(C2) vertebral three-dimensional image. Three virtual non-collinear markers were positioned on prominent structures of foramen magnum, C1 and C2. The 3D spatial coordinates of these virtual anatomical markers entail the definition of an anatomical local coordinate system which represent the position and orientation of the bones. Segmental motions were calculated using Eulerian angle in three major planes, and the difference between cervical spondylosis group and healthy adult group were compared. Due to the inaccuracy in anatomical landmark idenrification, two groups were measured 3 times, and the reliability of the experimental metnod was verified by the intra-group correlation (intra-group ICC) and the inter-group correlation coefficient(inter-group ICC)., Results: Reliability verification results:the intra-group ICC and inter-group ICC results were all above 0.90, and the measurement method had high reliability. Three-dimensional activity of the upper cervical spine in healthy adults:the atlanto-occipital joint had(-6.8±1.5)° coupled left lateral bending and (8.9±2.0)° coupled extension in the maximum right rotation position, and the motion of atlanto-occipital joint had low activity[maximum was(5.3±2.6)°] in the remaining 3 positions; the rotation of atlanto-axial joint was(37.9±5.1)°, accounting for 52.34% of the total cervical spine activity[(72.4±5.0)°] in the maximum right rotation position, and rotational motion was still prominent in the remaining three positions. The relative translations of the upper cervical spine in all direction were small. The average axial rotation angle [(62.0±3.4)] ° of the total cervical spine in cervical spondylosis group was significantly lower than that in the healthy adult group, but the mean axial rotation angles of the atlanto-occipital and the atlantoaxial joint were not significantly different from those of the healthy adults( P >0.05)., Conclusions: The three-dimensional CT reconstruction method has high reliability, which can be applied to measure the movement of spine. The upper cervical spine contributed the most to the direction of rotation, and the movement in all directions are accompanied by coupled motion in the other direction. There was no significant difference in the rotation of the upper cervical spine between cervical spondylosis patients and normal subjects., Competing Interests: The authors of this article and the planning committee members and staff have no relevant financial relationships with commercial interests to disclose., (Copyright© 2019 by the China Journal of Orthopaedics and Traumatology Press.)

Spinal biomechanics, especially the range of spine motion,has close connection with spinal surgery. The change of the range of motion (ROM) is an important indicator of diseases and injuries of spine, and the essential evaluating standards of effect of surgeries and therapies to spine. The analysis of ROM can be dated to the time of the invention of X-ray and even that before it. With the development of science and technology as well as the optimization of various types of calculation methods, diverse measuring methods have emerged, from imaging methods to non-imaging methods, from two-dimensional to three-dimensional, from measuring directly on the X-ray films to calculating automatically by computer. Analysis of ROM has made great progress, but there are some older methods cannot meet the needs of the times and disappear, some classical methods such as X-ray still have vitality. Combining different methods, three dimensions and more vivo spine research are the trend of analysis of ROM. And more and more researchers began to focus on vivo spine research. In this paper, the advantages and disadvantages of the methods utilized recently are presented through viewing recent literatures, providing reference and help for the movement analysis of spine.