Abstract:To compare the morphology of spinal cord between healthy adolescents with adolescent Chiari malformation type I (CMI) patients and investigate the impact of syringomyelia on the morphology of spinal cord in CMI patients.Methods:The clinical and radiological data of 292 CMI patients diagnosed by our center between June 2012 and March 2019 were retrospectively reviewed. Among them 15 CMI patients without syringomyelia were recruited in the CM group. Among the remaining 277 CMI patients, 274 patients had syringomyelia below the C 3-4 intervertebral disc. According to the principle of best matching, CMI patients with syringomyelia were selected with the closest age to the CM group (±18 months), and 30 CMI patients with syringomyelia were included in the CMS group according to a ratio of 1∶2. Thirty healthy adolescents were enrolled as the control group (NC group) in the same way. The anteroposterior diameters of spinal cord at C 2 (DSCO-C 2), spinal canal at C 2 (DSCA-C 2), midbrain-pontine junction (DPJ), the distance between the tip of cerebellar tonsils and the foramen magnum (AB) and the maximal diameter of the syrinx (D-syrinx) were measured on MRI. All radiographic parameters were measured twice independently by two spine surgeons, and intraclass correlation coefficient (ICC) were determined to demonstrate intra- and inter-observer reliability. One-way ANOVA and SNK- q test were used to compare the above radiographic parameters and age between CM, CMS and NC group. The distribution of genders was compared between the three groups using Chi-square tests. Pearson correlation analysis were conducted to demonstrate the relationship between radiographic parameters in CM and CMS group. Results:ICC ranged between 0.91 and 0.95 in the current study, demonstrating "excellent" reliability of radiographic measurements. No significant difference was noted regarding age and the distribution of genders among the three groups. Patients in CM and CMS groups showed similar DSCO-C 2 values ( P=0.254), both of which were significantly lower than that in NC group ( P<0.001). DSCA-C 2 in CMS group was significantly larger than that in CM ( P=0.003) and NC ( P<0.001) groups, while no significant difference was found between the CM and NC groups ( P=0.216). Moreover, DPJ in CMS group was significantly lower than that in CM group ( P<0.001) and NC group ( P<0.001). There was no significant difference in AB between CM and CMS groups ( P=0.948). DSCO-C 2 was significantly positively correlated with DSCA-C 2 in CMS group ( r=0.906, P<0.001), while AB, D-syrinx, DSCO-syrinx, DSCA-syrinx and DPJ were not significantly correlated with DSCA-C 2. There were significant correlations observed between DPJ and other radiographic parameters in the CMS group (all P>0.05). Significant positive correlation between DSCO-C 2 and DPJ was observed in CM group ( r=0.703, P=0.005). There was no significant correlation between DSCO-C 2 and DSCA-C 2 and DPJ in NC group (all P>0.05). Conclusion:CMI adolescents have significant atrophic change of cervical spinal cord and midbrain-pontine junction compared with healthy adolescents, regardless of the existence of syrinx. Moreover, syrinx in CMI patients indicated more obvious atrophic change of midbrain-pontine junction and dilated spinal canal compared with isolated CMI patients.

Objective:To investigate the radiographic risk factors related to the occurrence of distal adding-on (AO) in posteriorly treated Lenke modifier C adolescent idiopathic scoliosis (AIS) patients with the apical vertebra of the lumbar curve (L-AV) selected as the lowest instrumented vertebra (LIV).Methods:Seventy-three Lenke modifier C AIS patients were analyzed with a minimum of 2-year follow-up after posterior spinal fusion surgery with L-AV selected as LIV. Patients were grouped according to the occurrence of distal AO. Radiographical parameters were measured as follows: Cobb angle, curve flexibility and AV translation of the thoracic curve and lumbar curve, L-AV rotation and tilt, coronal balance, Harrington stable zone on anteroposterior (AP) film and concave bending film, L-AV derotation and L-AV/AV+1 disc opening or closing on convex bending film, etc. The Scoliosis Research Society-22 (SRS-22) score was used to evaluate clinical outcomes. Radiographic and clinical parameters were statistically analyzed between the two groups.Results:There were 23 patients in AO group and 50 patients in non-AO group. Preoperatively, the AO group had proximal L-AV, lower flexibility of the thoracic curve, coronal imbalance shifted to the convex side of the lumbar curve, lower Harrington stable zone on AP film and concave bending film, and less L-AV/AV+1 disc opening on convex bending film compared to non-AO group. The logistic regression revealed that the flexibility of the thoracic curve, coronal balance, Harrington stable zone on concave bending film, and L-AV/AV+1 disc opening or closing on convex bending film were significant predictors of distal AO. Specifically, the flexibility of the thoracic curve >40.0%, coronal balance< 19.6mm, and Harrington stable zone on concave bending film >77.8% might be optimal thresholds for selecting L-AV as LIV. At the final follow-up, AO group had larger lumbar curves and lower correction rates. No difference was found in the SRS-22 between the two groups.Conclusion:For Lenke modifier C AIS patients, LIV might be considered to stop at L-AV if there were good flexibility of the thoracic curves, coronal balance, L-AV/AV+1 disc opening on convex bending film, and large Harrington stable zone on concave bending film.