Radiographic classification of the lateral atlantoaxial joints in basilar invagination with atlantoaxial dislocation

English Keywords:Basilar invagination  Lateral atlantoaxial joints  Imaging classification

English Abstract:

  【Abstract】 Objectives: To analyze the three-dimensional CT imaging of craniocervical junction area in patients with basilar invagination with atlantoaxial dislocation, to propose the classification of the lateral atlantoaxial joints, and to explore its significance for the determination of surgical strategy. Methods: Retrospective analysis of patients with basilar invagination admitted to our hospital from June 2010 to June 2018, among which 115 patients were included as observation group (24 males, 91 females, aged from 12 to 74 years, mean age 46.7±12.8 years). 30 volunteers without occipitocervical lesions, matched by age and sex, were selected as control group (6 males and 24 females, aged from 14 to 76 years, mean age 45.8±9.4 years). The imaging data of the two groups were collected and the obliquity of the lateral atlantoaxial joint in coronal plane and sagittal plane was measured using three-dimensional CT. The obliquity in sagittal plane in the observation group outside of 95% CI of the control group was regared as sagittal tilting. And the obliquity in coronal plane outside of upper limit of 95% CI of the control group was regared as coronal tilting. Classification was made according to the obliquity of coronal and sagittal planes: type Ⅰ- no obliquity in both sagittal plane and coronal plane of the bilateral lateral atlantoaxial joint in the observation group; type Ⅱ-the obliquity was found in sagittal plane of unilateral or bilateral lateral atlantoaxial joint in the observation group; type Ⅲ-the obliquity was found in coronal plane of unilateral or bilateral lateral atlantoaxial joint in the observation group; type Ⅳ-the obliquity was found in sagittal and coronal plane in unilateral or bilateral lateral atlantoaxial joint, or the sagittal and coronal obliquity was found in bilateral lateral atlantoaxial joint respectively. The classification was modified according to the fusion and slippage of the lateral atlantoaxial joint: F0 is defined as no lateral mass joint fusion, F1 for small area bone fusion of anterior or posterior edge of lateral mass joint, and F2 for large area fusion of lateral mass joint; D0 for no slippage, D1 for coronal and sagittal partial slippage, D2 for complete slippage or joint interlocking. Reducibility of patients of observation group were evaluated under intraoperative traction, and the distribution of the irreducible patients in each type of lateral mass joint was assessed. The correlation between the types and the reducibility was analyzed. Results: The obliquity in coronal plane and sagittal plane of 60 lateral mass joints of 30 volunteers in the control group were 25.4°±4.1° and 2.4°±5.8°, respectively. The 95% CI of the obliquity in coronal plane in control group was 17.2°-33.6° (the obliquity in coronal plane in the observation group was greater than 33.6°, which was regarded as coronal tilt). The 95% CI of the obliquity in coronal plane in control group was -9.2°-14.0° (the obliquity in sagittal plane in the observation group less than -9.2° or gather than 14.0°, which was regarded as sagittal tilt). 115 Patients in the observation group were classified into 4 types: 22 cases (19.1%) as type Ⅰ, 59 cases (51.3%) as typeⅡ, 8 cases (7.0%) as type Ⅲ, and 26 cases (22.6%) as type Ⅳ. In type Ⅰ, there were 7 cases with D1 and no case with F1, F2 and D1. In TypeⅡ, 1 case with F1, 2 cases with F2, 42 with D1, 2 with D2. In Type Ⅲ, 1 with F1, 5 with D1, and no case with F2 and D2. In Type Ⅳ, 1 with F1, 1 with F2, 18 with D1, 3 with D2. Among the 40 patients with irreducible atlantoaxial dislocation, 2(9.1%)were type Ⅰ, 23(39.0%) were type Ⅱ, 3(37.5%) were type Ⅲ and 12(46.2%) were type Ⅳ. 40 patients of observation group were evaluated as irreducible under intraoperative traction. The percentage of irreducible type in type Ⅰ patientswas significantly lower than that of type Ⅱ patients and type Ⅳ patients(P<0.05). 11 cases with F1, F2 or D2 were irreducible. The percentage of irreducible type in patients with D1 or D2 was significantly higher than that of D0(P<0.05). Conclusions: The classification of lateral atlantoaxial joints in patients with basilar invagination based on imaging features of three-dimensional CT of lateral atlantoaxial joints is helpful to evaluate the reducibility before operation. It is also important to guide the intraoperative operation of lateral atlantoaxial joints.