Changes in Vertebral Axial Rotation after Thoracoscopic Scoliosis Correction

Abstract

Purpose: In this study, we investigated whether thoracoscopic anterior correction can effectively derotates the scoliotic spine and we also evaluated the patterns of derotational changes inside the instrumented area and at the junction between the instrumented and uninstrumented area. Materials and Methods: Preoperative and postoperative MR images with single axial cuts through each vertebral level were obtained in 20 patients who underwent thoracoscopic anterior instrumentation. Each vertebral rotation was measured by the use of Aaro's method. Vertebral axial derotation of the apical zone (AZ), upper instrumented zone (UIZ), lower instrumented zone (LIZ) and junctional segment were compared. The amount of segmental rotation and segmental derotation in each zone was calculated. Statistical analysis was performed by the use of by 2-way ANOVA and the Wilcoxon signed ranks test. Results: The average axial rotations at AZ were 10.1 o preoperatively and 5.3 o postoperatively with an average correction rate of 48%. Derotation of the AZ was greater than the UIZ and LIZ. For the LIZ derotation was not significant (p=0.023) while for the UIZ there was a significant derotation (p<0.001). Postoperatively, the first uninstrumented vertebra rotated significantly in the direction of rotation of the instrumented end vertebra. Preoperative and postoperative segmental rotation was higher in the UIZ and LIZ than in the AZ. However, segmental derotation occurred uniformly in the instrumented area. At the junctional segment, preoperative segmental rotation was same as that of the UIZ and LIZ and segmental derotation was not significant. Conclusion: Thoracoscopic scoliosis correction can achieve effective axial correction by causing dero- tation of each of the vertebral bodies and segmental derotation.