Importance of Distal Fusion Level in Major Thoracolumbar and Lumbar Adolescent Idiopathic Scoliosis Treated by Rod Derotation and Direct Vertebral Rotation Following Pedicle Screw Instrumentation

Study Design. A retrospective comparative study. Objective. The aim of this study was to analyze the exact distal fusion level in the treatment of major thoracolumbar and lumbar (TL/L) adolescent idiopathic scoliosis (AIS) using rod derotation (RD) and direct vertebral rotation (DVR) following pedicle screw instrumentation (PSI). Summary of Background Data. Proper determination of distal fusion level is a very important factor in deformity correction and preservation of motion segments in the treatment of major TL/L AIS. Methods. AIS patients with major TL/L curves (n=64) treated by PSI with RD and DVR methods with a minimum 2-year follow-up were divided into AL3 (flexible) and BL3 (rigid) according to the flexibility and rotation by preoperative bending radiographs. Results. There was no significant difference in TL/L (major) curve between the AL3 and BL3 groups postoperatively (P=0.933) and at the last follow-up (P=0.144). In addition, there was no significant difference in thoracic (minor) and compensatory (caudal) curve postoperatively (thoracic curve: P=0.828, compensatory curve: P=0.976); however, there was a significant difference in compensatory (caudal) curve at the last follow-up (P=0.041). The overall prevalence of unsatisfactory results was 28.1% (18/64 patients), and the prevalence was 15.2% (7/46) in the AL3 group and 61.1% (11/18) in the BL3 group, which was significantly different (P<0.05). Conclusion. Lowest instrumented vertebra (LIV) would be selected at L3 (EV) when the curve is flexible; L3 crosses CSVL with a rotation of less than grade II in preoperative bending radiographs. However, if the curve is rigid, LIV should be extended to L4 (EV+1) in order to prevent the adding-on phenomenon in the treatment of major TL/L AIS using RD and DVR following PSI.