The Proximal Humerus Ossification System Predicts Surgical Curve Progression in Unbraced Patients With Adolescent...

Curve progression to surgical range in patients with adolescent idiopathic scoliosis (AIS) is strongly associated with the initial major curve angle and the degree of skeletal maturity as staged by the modified Proximal Humerus Ossification System (PHOS) and other systems. Our purpose was to (1) develop a prognostic model and risk score to estimate the probability of progression to surgical indications in untreated patients using the PHOS and (2) compare its performance to a model using the Risser stage.

Patients from the BrAIST study and 2 other institutions were followed to either skeletal maturity (Risser 4+), a major curve angle of ≥45°, or spinal fusion. Candidate variables for the predictive models included age, sex, major curve angle, Scoliosis Research Society (SRS) curve classification, status of triradiate cartilage, Risser stage, and PHOS. Model calibration and discrimination were evaluated. A probability threshold was set, creating low- and high-risk groups to aid in clinical decision-making.

Overall, 164 patients (77% female) were included. The mean age at presentation was 12.2±1.4 years (range: 10 to 16 years), and the mean maximum major curve angle was 24±9° (range: 10° to 43°). Fifty-six (34%) patients progressed to a surgical range or had a spinal fusion. The PHOS model included the major curve angle and the presence/absence of a thoracic apex. The model demonstrated strong discrimination (c-statistic = 0.89) and calibration (ICI = 0.02), performing similarly to one developed in this sample using the Risser stage. The sensitivity was 0.91, the specificity was 0.71, the PPV was 0.62, and the NPV was 0.94 at the probability cut-point of 0.22.

This study derived a prognostic model estimating the baseline risk of progression to surgical indications in AIS patients using the PHOS. Estimates from this model can inform the shared decision-making process and motivate compliant bracing. Further validation in larger independent samples and exploration of the PHOS to predict bracing outcomes should be performed.

Level II.