In-brace correction but not coronal deformity angular ratio is associated with curve progression in nighttime brace treatment for adolescent idiopathic scoliosis.

PURPOSE: To determine whether in-brace correction (IBC) and coronal deformity angular ratio (CDAR) differ by curve location and whether they predict curve progression.

METHODS

A retrospective review was conducted of 282 AIS patients ages 10-16, with Risser 0-2, curves 15°-40° prescribed Providence nighttime braces between 2015 and 2019 with IB radiographs. Patients were followed to skeletal maturity or surgical magnitude. IBC was calculated by comparing standing brace prescription radiographs and supine in-brace radiographs. CDAR was defined as Cobb angle divided by the number of vertebrae in the primary curve. Curve location (thoracic [T], thoracolumbar [TL], or lumbar [L]) was defined by the primary curve apex. Multivariate logistic regression evaluated associations between IBC, CDAR, and curve progression (≥ 6°).

RESULTS

Thoracolumbar curves demonstrated greater IBC than thoracic or lumbar curves (113% vs. 88% vs. 94%, p < 0.001), while lumbar curves had higher CDAR (4.6 vs. 4.2 vs. 3.3, p < 0.001). On multivariate analysis, decreased IBC (OR 0.12, 95% CI 0.04 - 0.36) and open triradiate cartilage (OR 2.73, 95% CI 1.56 - 4.88) were independently associated with curve progression. CDAR was not predictive. ROC analysis identified an IBC threshold of 93% for successful treatment (AUC = 0.65).

CONCLUSION

In Providence nighttime bracing, IBC is an important modifiable risk factor for curve progression, whereas CDAR is not. Maximizing IBC at brace fitting, particularly in skeletally immature patients with open triradiates, may improve treatment success and reduce progression risk.