A method to evaluate the reduction difficulty of atlantoaxial dislocation based on CT quantitative analysis

To evaluate the difficulty of reduction of congenital atlantoaxial dislocation (AAD) with/without os odontoideum or basilar invagination (BI) based on CT quantitative analysis. From March 2018 to December 2022，the CT features of 108 patients with AAD with/without os odontoideum or BI were analyzed. Quantitative scores were defined according to imaging features, including: sloping of the lateral mass, osteophyte between the lateral mass joint, ball-and-socket deformity of the lateral mass joint, vertical interlocking of the lateral mass joint, callus between the lateral mass joint, atlanto-odontoid joint hyperplasia, blocking or fusion. Grades were as follows according to the sum of points of the atlanto-odontoid joint and lateral mass joints: Grade I, 0-1 points; Grade Ⅱ, 2-3 points; Grade Ⅲ, 4-6 points; and Grade IV, 7-10 points. After one week of bidirectional cervical traction, CT scans were performed and atlantodens interval (ADI) and vertical distance from dens to Chamberlain line (VDDC) were measured. The vertical reduction rate, horizontal reduction rate and overall reduction rate of atlantoaxial dislocation were calculated. The after-traction VDDC values were significantly reduced than that of pre-traction, including grade I, II, III and IV. The overall reduction rates were respectively 85.1±11.8%, 65.8±8.3%, 45.0±8.5% and 38.4±13.0% after one-week of bi-directional cervical traction. The CT quantitative score system is an effective non-invasive evaluation of judging the reduction difficulty of AAD with/without os odontoideum or BI.