The predictive value of the fulcrum bending radiograph in spontaneous apical vertebral derotation in adolescent idiopathic scoliosis.

STUDY DESIGN: A prospective cohort study of Cobb angles (CA) and apical vertebral rotations (AVR) in 25 patients who had adolescent idiopathic scoliosis. OBJECTIVE: To assess in vivo the concomitant vertebral derotation occurring with correction of scoliosis deformity as a result of coupling effect by using the fulcrum bending radiograph and to assess whether the fulcrum bending radiograph can predict the amount of postoperative apical derotation when no additional intraoperative apical derotation maneuver is used. SUMMARY OF BACKGROUND DATA: Adolescent idiopathic scoliosis (AIS) is a 3-dimensional coupling deformity. Various studies have reported vertebral derotational effects, using different implant constructs and surgical techniques for AIS. However, none of them have considered the spontaneous coupling effect on vertebral derotation produced by correction of the coronal deformity, in particular, using the predictive capacity of the preoperative fulcrum bending radiograph. METHOD: Twenty-five patients with flexible Lenke type 1 AIS with CA greater than 45° who underwent posterior spinal fusion with instrumentation, without direct apical derotation were prospectively assessed. CA and AVR in standing, supine, and fulcrum bending positions preoperatively and in supine position postoperatively were assessed on radiographs and computed tomographic scans. RESULTS.: The study entailed 80% adolescent girls and 20% adolescent boys (mean age, 15.5 years). The mean AVR values on preoperative standing, supine, and fulcrum bending positions and postoperation were 24.2°, 17.7°, 9.8°, and 8.1° respectively. The preoperative AVR highly correlated with the preoperative CA (R = 0.75). The postoperative AVR was correlated with the postoperative CA (r = 0.82) and the change in curve magnitude (r = -0.49), correction rate (r = -0.83), and fulcrum bending correction index (r = -0.45) (P < 0.05). There was no significant difference in AVR between preoperative fulcrum bending and postoperative assessment. CONCLUSION: Correction of scoliosis deformity produces spontaneous reduction of rotational deformity through coupling. The amount of spontaneous apical vertebral derotation with fulcrum bending can be used to assess the flexibility of the rotational deformity. In flexible curves, it also predicts the amount of apical derotation achievable with surgery. These should be considered when assessing the derotational effect of different implants and surgical strategies.