Journal of Pediatric Orthopaedics - 2026-04-01 - Journal Article
The Proximal Humerus Ossification System Predicts Surgical Curve Progression in Unbraced Patients With Adolescent Idiopathic Scoliosis.
Taylor TN, Ratnasamy PP, Lee TM, Tuason D, Li DT, Cooperman DR, Dolan LA, Smith BG
Topics
Key Takeaway
A PHOS-based prognostic model predicts surgical curve progression in unbraced AIS patients with a c-statistic of 0.89 and NPV of 0.94, performing equivalently to a Risser-based model.
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Summary
This study derived a prognostic model using PHOS, major curve angle, and thoracic apex presence to predict progression to surgical indications in unbraced AIS patients. Of 164 patients (mean age 12.2 years, mean curve 24°), 34% progressed to surgical range or underwent fusion. The PHOS model achieved c-statistic 0.89, sensitivity 0.91, NPV 0.94, and performed equivalently to a Risser-based model built on the same sample.
Key Limitation
The model was derived and tested in the same 164-patient cohort without external validation, so reported performance metrics are optimistic and cannot yet be applied to independent clinical populations.
Original Abstract
BACKGROUND
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.
METHODS
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.
RESULTS
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.
CONCLUSIONS
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.
DIAGNOSTIC STUDY
Level II.