Imaging Classification Of The Lateral Atlantoaxial Joints In Basilar Invagination With Atlantoaxial Dislocation

Objective:To analyze the three-dimensional CT imaging of craniocervical junction in patients with basilar invagination with atlantoaxial dislocation,and to propose the classification of the lateral atlantoaxial joints.Methods:From June 2010 to June 2018,115 patients with basilar invagination were admitted to our hospital.Among them,24 were males and 91 were females,aged from 12 to 74 years?46.7±12.8 years?.Thirty volunteers matched by age and sex without occipitocervical lesions were selected as control group.Among them,6 were males and 24 were females,aged from 14to 76 years?45.8±9.4 years?.The imaging datas of the two group were observed and the obliquity of the lateral atlantoaxial joint in coronal plane and sagittal plane was measured in three-dimensional CT.The obliquity in coronal plane and sagittal plane of the observation group was used as the basis indexes to develop the classification of the lateral atlantoaxial joint.Fusion and olisthy of the lateral atlantoaxial joint were used as the modified index of classification.The obliquity in sagittal plane in the observation group inside of bilateral 95%CI of the control group and the obliquity in coronal plane inside of unilateral95%CI of the control group,which was regared as type I.Classification was made according to the obliquity of coronal and sagittal planes:the obliquity in sagittal plane in the observation group inside of 95%CI of the control group and the obliquity in coronal plane less than the upper limit of 95%CI of the control group,which was regared as type I.The obliquity in sagittal plane in the observation group outside of 95%CI of the control group and the obliquity in coronal plane less than the upper limit of 95%CI of the control group,which was regared as type II.The obliquity in sagittal plane in the observation group inside of 95%CI of the control group and the obliquity in coronal plane greater than the upper limit of 95%CI of the control group,which was regared as type III.Bilateral lateral atlantoaxial joints were type II and type III respectively or one side was type II and III,which was regared as type IV.The classification was modified according to the fusion and olisthy of the lateral atlantoaxial joint:F₀ for 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 olisthy,D₁ for coronal and sagittal partial olisthy,D₂ for complete olisthy or joint interlocking.115 patients of observation group were evaluated as irreducible under intraoperative traction,and the distribution of 40 patients in each type of lateral mass joint was counted.The correlation between the type 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.Unilateral 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 greater than 33.6°,which was regarded as coronal tilt?.Bilateral 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?.Patients in the observation group were divided into 4 types.Twenty-two cases?19.1%?were type I;59 cases?51.3%?were type II;8 cases?7.0%?were type III;26 cases?22.6%?were type IV.In type I,there were 7 cases with D₁ and no case with F₁,F₂ and D₁.Type II with F₁ 1 cases,F₂ 2 cases,D₁ 42 cases,D₂ 2cases.Type III with F₁ 1 case,D₁ 5 cases,and no cases with F₂ and D₂.Type?with F₁ 1 cases,F₂ 1 cases,D₁ 18 cases,D₂ 3 cases.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.The proportion of irreducible type in patients with type I was significantly lower than that of patients with type II and type IV?p<0.05?.11 cases with F₁,F₂ or D₂ were irreducible.The proportion of irreducible type in patients with D₁ or D₂ is significantly higher than that of D₀?p<0.05?.Conclusion: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 preoperatively.It is also important to guide the intraoperative operation of lateral atlantoaxial joints.