Standardized traction versus side-bending radiographs in adolescent idiopathic scoliosis: a preliminary study

The aim of this study was to develop a new type of preoperative flexibility test for adolescent idiopathic scoliosis. The objective was to develop a test that was standardized and allow for the measurement of in-vivo forces required for curve correction. It was undertaken to compare the results of this new test with side-bending radiographs. Various preoperative radiographic techniques have been used to assess flexibility in patients awaiting scoliosis correction surgery. The major limitation of these investigations is a lack of standardization. The side-bending radiograph is the current gold standard, against which this new test was compared. A prospective clinical study was conducted. An axial traction force of 1.5 times body weight was applied through the spine of patients using a traction jig. Posteroanterior, side-bending and traction radiographs were taken. Cobb angle and apical vertebra axial rotation measurements were obtained. Flexibility indices in the coronal and axial planes were calculated. Cobb angle reduction and axial derotation were compared between the two methods. A total of 15 (12 female and three male) patients, with a mean age of 15.1 years, were assessed. The mean force imparted on traction films was 800 N. The major curve Cobb angle measurements were 60.4° on standing posteroanterior radiograph, 52.7° on side-bend film and 44.5° on traction at 1.5 times body weight. The corresponding apical vertebrae axial rotations were 23.9°, 22.2° and 16.5°, respectively. The mean Cobb angle reduction was 15.9 for traction and 7.7 for side-bend radiographs (P<0.0001). The mean apical vertebra derotation was 7.4 for traction and 1.7° for side-bend radiographs (P=0.0083). The mean flexibility index in the coronal plane was 0.479. The mean flexibility index in the axial plane was 0.240. Our novel method of traction radiographs at 1.5 times body weight is a safe and reproducible method of assessing curve flexibility in patients with scoliosis. This method achieves a larger Cobb angle and axial derotation when compared with side-bending radiographs.