Factors affecting Distal End & Global Decompensation in Coronal/Sagittal Planes 2 years after Fusion

Introduction: Decompensation of un-fused vertebrae is a potential complication of spinal instrumentation performed for adolescent idiopathic scoliosis (AIS). This can result in problems requiring revision surgery. The purpose of this study was to compare patients who decompensated in the sagittal/coronal plane and those who do not and to identify risk factors. Methods: The Spinal Deformity Study Group data-base for AIS identified 908 patients at 2 years post-op. Coronal measures analyzed included coronal balance (CB), coronal position of the lower instrumented vertebra (CPL) and LIV tilt angle (LTA). Sagittal measures included sagittal balance (SB) and distal-junctional kyphosis (DJK). The incidence of decompensation at 2 years was: CB-16.83%, LTA-37.53%, CPL-21.17%, negative SB-51.88%, positive SB-7.62%, DJK-6.8%. Decompensated patients were compared to those who were not using preoperative, and 4-16 weeks post-op values. Results: Numerous significant differences were found between patients who decompensated at 2 years and those who did not. CB was significantly influenced by larger height/weight, increased Cobb, preexisting CB and a thoracic LIV. In addition to other factors LTA decompensation was more likely to occur in JIS. CPL was associated with pelvic-obliquity and thoracic LIV. Post-operative sagittal balance could be predicted by pre-operative sagittal balance. DJK was also associated with larger weight and preoperative sagittal measures. Discussion and Conclusion: Less correction in sagittal/coronal planes is a risk factor for decompensation. Curve correction was significant in predicting coronal decompensation. Failure to control sagittal alignment was a risk factor in sagittal decompensation.