Determination of optimal screw number based on correction angle for main thoracic curve in adolescent idiopathic scoliosis

Background: Reducing the number of screw insertions while maintaining good clinical outcomes can improve the efficiency and cost-effectiveness of scoliosis surgery. However, the optimal minimum number of pedicle screws remains unclear. This study searched for factors to estimate the fewest number of pedicle screws required between end vertebrae in relation to preoperative main thoracic curve flexibility. Methods: Sixty-nine subjects (4 male and 65 female, mean age: 14.8 +/- 2.5 years) who underwent skip pedicle screw fixation for Lenke type 1-4 or 6 curves and were followed for at least 1 year were enrolled. Intervention technique was selected according to the size and flexibility of the preoperative main thoracic curve. Surgery-related variables included pedicle screw number, rod material and diameter, and extent of Ponte osteotomy. The effect on postoperative correction angle (i.e., the difference between the preoperative supine position maximum bending and postoperative standing Cobb angles of the main thoracic curve) according to surgical intervention technique was estimated using multiple linear mixed regression models with the preoperative supine position maximum bending correction angle (i.e., the difference between the standing preoperative and supine position maximum bending Cobb angles) as a random effect. Results: The preoperative maximum bending correction angle was 8-42 degrees and had a moderate negative correlation with postoperative correction angle (r = -0.65, P < 0.01). Multivariate analysis revealed a 1.7 degrees (95% CI 0.7-2.6; P < 0.01) correction gain per single-screw insertion and a 1.8 degrees (95% CI 0.5-3.1; P < 0.01) gain per intervertebral level in Ponte osteotomy. Conclusions: The number of pedicle screws necessary to correct main thoracic adolescent idiopathic scoliosis curves can be estimated by calculating correction gains of 1.7 degrees per pedicle screw and 1.8 degrees per Ponte osteotomy intervertebral level. Based on these results, it may be possible to reduce invasiveness and cost for patients requiring a smaller degree of correction. (c) 2018 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.