ABSTRACT
<p><b>OBJECTIVE</b>To provide quantitative foundation for the diagnosis of atlanto-axial rotatory subluxation by analyzing the various imaging features of normal atlanto-axial joints in neutral position and rotary functional position on the MSCT images.</p><p><b>METHODS</b>Forty-one normal volunteers were examined by CT on the atlanto-axial joint in neutral position and rotary functional position. By the observation and measurement of atlanto-dental interval (ADI), lateral atlanta-dental space (LADS), VBLADS and rotating angle of atlas on dentate (RAAD), the imaging manifestations and anatomical characteristics were analyzed and compared. In order to compare VBLADS and RAAD and make a correlation analysis between different age groups, 51 normal volunteers were divided into two groups: age younger than 45 years old group and age older than or equal to 45 years old group.</p><p><b>RESULTS</b>The dens in neutral position deviated in an angle range of (3.22±0.89)°. The articular facets of lateral atlantoaxial joint in rotary functional position had rotatory displacement and the range of the relative rotation angle was (33.85± 2.79)°. Through the correlation analysis of matching data, it could be concluded that there was no correlation between atlantoaxial relative rotation angle and VBLADS within a certain range. There were statistically differences of atlantoaxial relative rotation angle in rotary functional position between two groups.</p><p><b>CONCLUSION</b>MSCT imaging in rotary functional position can clearly show the anatomical structure and rotation function of a normal atlanto-axial joint, so as to provide a theoretical basis for the diagnosis of atlanto axial rotatory subluxation.</p>