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.: 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). Additionally, 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). CONCLUSIONS.: 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.Level of Evidence: 4