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

Abstract Background To evaluate the difficulty of reduction of atlantoaxial dislocation based on CT quantitative analysis, and to provide guidance for surgical decision-making. Methods From March 2018 to December 2019, the CT features of 88 patients with atlantoaxial dislocation were analyzed retrospectively. Quantitative scores were defined according to imaging features, including: 0 point, flat and horizontal lateral mass joints; 1 point, slightly sloped lateral mass joints; 1.5 points, more severe sloped lateral mass joints; 2 points, osteophyte in atlantoaxial joint; 3 points, ball-and-socket deformity, interlocking, callus in atlantoaxial joint, and atlanto-odontoid bony fusion or blocking. The total scores of lateral mass joints and atlanto-odontoid joints on both sides were calculated separately. 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, 7–9 points. After one week of bidirectional cervical traction, CT scans were peformed and atlantodens interval (ADI) and vertical distance from dens to Chamberlain line (VDDC) were measured before and after traction. The vertical reduction rate, horizontal reduction rate and overall reduction rate of atlantoaxial dislocation were calculated. The difference in reduction rate of each grade was compared and the value of CT quantitative score in judging the degree of reduction were analyzed. Results Of the 88 patients, the pre- and after- traction ADI values showed 15 cases of grade I ( 7.3 ± 3.4 mm vs 1.5 ± 1.5 mm, p < 0.05), 23 cases of grade II ( 8.1 ± 3.7 mm vs 2.0 ± 1.0 mm, p < 0.05), 38 cases of grade III ( 8.8 ± 4.1 mm vs 5.7 ± 1.7 mm, p < 0.05) and 12 cases of grade IV ( 8.9 ± 3.9 mm vs 6.8 ± 3.6 mm, p > 0.05). The pre-traction VDDC values were improved than that of after-traction, including grade I (11.9 ± 3.9 mm vs 0.8 ± 0.5 mm, p < 0.05), grade II (12.2 ± 3.6 mm vs 3.1 ± 1.1 mm, p < 0.05), grade III (13.6 ± 3.8 mm vs 5.9 ± 1.5 mm, p < 0.05) and grade IV (12.3 ± 3.2 mm vs 8.2 ± 2.0 mm, p < 0.05). The overall reduction rates were respectively 86.4 ± 12.0%, 67.6 ± 8.0%, 45.9 ± 9.0% and 28.4 ± 13.0% after one week of bi-directional traction of the skull, and the statistical differences between groups were significant (p < 0.05). Conclusions The CT quantitative scores can help judge the difficulty of atlantoaxial reduction and provide a reference for surgical decision-making. It is an effective non-invasive preoperative evaluation for the difficulty of reduction of atlantoaxial dislocation.