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.