Supine Lateral Bending Radiographs Predict the Initial In-brace Correction of the Providence Brace in Patients With Adolescent Idiopathic Scoliosis.

STUDY DESIGN Retrospective, cross-sectional. OBJECTIVE To determine the initial curve correction of the providence brace (PB) and to determine to what extend the in-brace Cobb angle corresponds to the curve seen on supine lateral bending radiographs (SLBR). SUMMARY OF BACKGROUND DATA SLBR are used to assess curve flexibility in patients undergoing surgical treatment for adolescent idiopathic scoliosis (AIS). A low rate of in-brace correction (IBC) has been associated with a higher risk of curve progression, but to what extent SLBR can be used to predict IBC before initiating bracing treatment is unknown. METHODS All patients with AIS treated with the PB from January 1, 2006 to December 31, 2013 with a major curve of 25 to 45 degrees° were included. Cobb angle on SLBR before treatment and on initial standing, in-brace radiograph (IBR) were measured twice for each patient by one observer 30 days apart. Using a repeated measure mixed effect model, mean difference and 95% limits of agreement (LOA) between Cobb angles on each type of radiograph were estimated. Correction index (CI) was calculated as: curve flexibility (%)/curve correction (%). RESULTS A total of 127 patients were included. Mean long-standing Cobb angle was 35° (SD: 6°), which was reduced to mean 13° (SD: 8) on IBR (P < 0.05). No difference in curve correction between curve types was found when adjusting for flexibility using correction index (P = 0.77). Overall mean difference between SLBR and IBR was 0.2° (LOA ± 10°). Mean difference for thoracic curves was 0.2° (LOA ± 8°), for thoracolumbar/lumbar curves 0.9° (LOA ± 10°) and for double major curves 0.4° (LOA ± 16). CONCLUSION SLBR provide a close estimation to the expected in-brace correction with a mean difference of less than one degree. SLRB could potentially serve as prognostic parameter for curve progression before initiating brace treatment. LEVEL OF EVIDENCE 3.