Prediction of postoperative trunk imbalance after posterior spinal fusion with pedicle screw fixation for adolescent idiopathic scoliosis

The objective of this retrospective study was to explore, which radiographic parameters, immediately after posterior spinal fusion with pedicle screw fixation for adolescent idiopathic scoliosis (AIS), best correlate with subjacent disc wedging at a minimum of 2-year follow-up. Sixty-four consecutive AIS patients who underwent posterior pedicle screw-only instrumentation were studied. Preoperative and postoperative radiographs were obtained to measure various parameters regarding global coronal, shoulder, sagittal, and regional balance. Specific correlation of these parameters to selected 2-year postoperative disc wedging and lowest-instrumented vertebra (LIV) tilt and translation were analyzed. The average lateral disc opening changed from 4.59 +/- 4.75 preoperatively to 1.46 +/- 2.82 at 2 weeks and 2.81 +/- 6.43 at 2 years postoperatively. Two-year postoperative lateral disc opening significantly correlated with the 2-week postoperative lateral disc opening, C7 plumbline relative to the posterior-superior corner of the first sacral vertebra distance, and LIV-center sacral vertical line (CSVL) distance (r(2) = 0.7433, P < 0.0001). The two-year postoperative LIV tilt significantly correlated with the 2-week postoperative LIV tilt, T12-LIV lordosis, LIV-CSVL distance, and C7-CSVL distance (r(2) = 0.8879, P < 0.0001). Two-year postoperative LIV-CSVL significantly correlated with 2-week postoperative LIV-CSVL distance and lateral disc opening (r(2) = 0.6104, P < 0.0001). Two-year postoperative disc wedging, LIV tilt, and LIV translation occurred most often when disc wedging and LIV deviation or obliquity existed immediately postoperatively. This study identified a potential indicator for AIS repair. Preoperative surgical planning and intraoperative correction are important for avoiding subjacent regional imbalance after scoliosis fusion. J Pediatr Orthop B 20: 199-208 (C) 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins.