Assessment of Curve Flexibility in Adolescent Idiopathic Scoliosis

Purpose: Along with magnitude, flexibility of a scoliotic curve has always been a major determinant for preoperative planning and surgical outcome for adolescent idiopathic scoliosis (AIS). The purpose of this study was to use and evaluate mostly accepted or described radiologic techniques or methods to determine flexibility and compare the results to those obtained by supine traction X-rays under general anesthesia just before surgery and correlate all findings to surgical correction.

Methods: 34 consecutive AIS patients who had surgical treatment were studied. 25 were female, 9 were male and average age was 15.7 (12-19) years. Preoperative radiologic evaluation consisted of standing AP and lateral, supine lateral bending and traction, fulcrum X-rays and also supine traction X-rays under general anesthesia (GA) just before surgery. All structural curves were measured and flexibility ratio was determined on each radiograph. Calculated values were correlated with amount of surgical correction achieved by pedicle screw instrumentation.

Results: Curves were accepted to be moderate if between 40° and 65° (29 patients) and severe if >65° (5 patients). In these 29 patients, average frontal Cobb angle of the thoracic and lumbar curves were 39.7° (40°-60°) and 39.4° (22°-58°) respectively. Average thoracic curve flexibility was 49% (23%-64%) at traction, 79% (30%-88%) at traction under GA, 66% (25%-82%) upon lateral bending and 74% (50%-87%) at fulcrum X-rays. Average surgical correction of the thoracic curve was 76% (52%-95%). Average lumbar curve flexibility was 56% (35%-73%) at traction, 59% (39%-72%) at traction under GA, 81% (61%-100%) upon lateral bending and 83% (66%-100%) at fulcrum Xrays. Average surgical correction of the lumbar curve was 74% (44%-100%). In the other group of 5 patients, average frontal Cobb angle of the thoracic and lumbar curves were 79° (47°-110°) and 67° (38°-90°) respectively. With the same order above, average thoracic curve correction was 35% (29%-38%), 52% (49%-58%), 43% (35%-55%) and 45% (41%-50%). Also average lumbar curve correction was 40% (32%-50%), 60% (45%-79%), 51% (40%-65%), 53% (38%-69%). Average surgical correction of the thoracic and lumbar curve in this group were 68% (64%-72%) and 63% (42%-79%) respectively.

Conclusion: Traction under GA > fulcrum > bending > seems to be the order of X-rays for better predicting flexibility and correction in curves > 65°. Pedicle screw instrumentation however provides even more correction than are obtained by traction under GA. On the other hand fulcrum > bending > traction under GA > is the order of X-rays for better predicting flexibility and correction in curves between 40°-65°. Amount of surgical correction in this group is either close or equivalent to correction at fulcrum x-rays. Traction X-ray under GA may show much better flexibility and thus, it may eliminate the need for anterior surgery in seemingly rigid, > 65° curves.