Cervical lordotic alignment following posterior spinal fusion for adolescent idiopathic scoliosis: reciprocal changes and risk factors for malalignment

OBJECTIVE Numerous reports have been published on the effectiveness and safety of correction of the coronal Cobb angle and thoracolumbar sagittal alignment in patients with adolescent idiopathic scoliosis (AIS). Suboptimal sagittal alignment, such as decreased thoracic kyphosis (TK), after corrective surgery, is a possible cause of lumbar or cervical spinal degeneration and junctional malalignment; however, few reports are available on reciprocal changes outside of the fused segments, such as the cervical lordotic angle (CLA). This study aimed to investigate the relationship between the perioperative CLA and other radiographic factors or clinical results in AIS, and to identify independent risk factors of postoperative cervical hyperkyphosis. METHODS A total of 51 AIS patients who underwent posterior spinal fusion with the placement of pedicle screw (PS) constructs at thoracic levels were included in the study. Clinical and radiographic follow-up of patients was conducted for a minimum of 2 years, and the postoperative course was evaluated. The authors measured and identified the changes in the CLA and other radiographic parameters using whole-spine radiography, with the patient in the standing position, performed immediately before surgery, 2 weeks after surgery, and 2 years after surgery. The postoperative cervical hyperkyphosis group included patients whose CLA at 2-year follow-up was smaller than -10 degrees. The reciprocal changes of the CLA and other parameters were also investigated. Univariate and multivariate analyses were conducted to determine the associated risk factors for postoperative cervical hyperkyphosis. RESULTS This study comprised 48 females and 3 males (mean age 16.0 years). The mean follow-up period was 47 months (range 24-90 months). The main corona! thoracic curve was corrected from 54.6 degrees to 16.4 degrees, and the mean correction rate was 69.8% at 2 years. The CLA significantly increased from the mean preoperative measurement (-5.4 degrees +/- 14 degrees) to the 2 -year follow-up measurement (-1.7 degrees +/- 11 degrees) (p = 0.019). Twelve of the 51 patients had postoperative cervical hyperkyphosis. This group exhibited significantly smaller preoperative CLA and TK measurements (p = 0.001 and 0.004, respectively) than the others. After adjusting for confounding factors, preoperative CLA less than -5 degrees and preoperative TK less than 10 were significantly associated with postoperative cervical hyperkyphosis (p < 0.05; OR 12.5 and 8.59, respectively). However, no differences were found in the clinical results regardless of cervical hyperkyphosis. CONCLUSIONS The CLA increased significantly from preoperatively to 2 years after surgery. Preoperative small CLA and TK measurements were independent risk factors of postoperative cervical hyperkyphosis. However, there was no difference in the clinical outcomes regardless of cervical hyperkyphosis.