Inner sagittal diameter and morphologic classification of developmental canal stenosis at the level of the atlas in the adult / 中华骨科杂志

ABSTRACT

Objective@#To provide the normal value of atlas (C1) inner sagittal diameter in adults thus defining the diagnostic value of developmental canal stenosis at C1 and to establish the Jishuitan (JST) morphological classification for C1 developmental canal stenosis in craniovertebral junction (CVJ) anomalies.@*Methods@#From December 2010 to November 2018, 101 patients with various CVJ anomalies (50 males, 51 females; mean age 48.8±12.9 years, range 15-78 years; the anomaly group) and 857 patients with normal CVJ (461 males, 396 females; mean age 50.2±8.3 years, range 21-79 years; the normal group) were enrolled in a retrospective study. In the anomaly group, 92 cases of atlantoaxial dislocation were furtherly divided into three subgroups according to Wadia classification atlantoaxial dislocation with os odontoideum (OO subgroup, n=33), atlantoaxial dislocation with occipitalization of the atlas (OA subgroup, n=24), atlantoaxial dislocation without both OO and OA (AAD subgroup, n=35); the rest of the anomaly group was combined with Chiari malformation (CM subgroup, n=9). The range of C1 inner sagittal diameter in each group was measured via CT scan images. The normality of C1 inner sagittal diameter of each group was tested via Shapiro-Wilk method. T test was performed on C1 inner sagittal diameter of each group. The diagnostic value of C1 developmental canal stenosis was defined as the lower bound of 95% confidence interval (CI) for the mean of the normal group. The C1 morphology of developmental canal stenosis cases in anomaly group were analyzed via CT scan images thus establishing the JST morphological classification for C1 developmental canal stenosis in CVJ anomalies.@*Results@#The mean C1 inner sagittal diameter was 29.05±1.60 mm (range, 24.05-33.50, 95%CI 25.91-32.19). C1 developmental canal stenosis was defined as C1 inner diameter ≤ 25.91 mm. The mean C1 inner sagittal diameter of the whole anomaly group was 26.84±2.04 mm (95%CI 22.84-30.84), which differed significantly from that in the the normal group (t=10.504, P< 0.01). A total of 33 cases meeting the criteria of C1 inner diameter ≤ 25.91 mm were diagnosed as C1 developmental canal stenosis, including 14 cases of the OO subgroup, 4 cases of the OA subgroup, 15 cases of the AAD subgroup and none of the CM subgroup. Based on the C1 morphological characteristics of 33 cases, the JST classification of C1 developmental canal stenosis in CVJ anomalies was established, which could be divided into type I-III. Type I little atlas type, 84.9% (28/33), normal C1 posterior arch morphology without C1 occipitalization; Type II atlas posterior arch incurving type, 3.0%(1/33), C1 posterior arch incurves towards spinal canal, without C1 occipitalization; Type III atlas occipitalization type, 12.1% (4/33), furtherly divided into type IIIa with normal C1 posterior arch morphology; type IIIb with incurving C1 posterior arch.@*Conclusion@#The normal value of C1 inner sagittal diameter in adults was from 24.05 to 33.50 mm. The criteria of C1 inner sagittal diameter ≤ 25.91 mm can be used as the radiographic diagnostic value of C1 developmental canal stenosis. C1 developmental canal stenosis in CVJ anomalies can be classified according to the JST classification system.