Bracing in Adolescent Idiopathic Scoliosis Trial (BrAIST): Development and Validation of a Prognostic Model in Untreated Adolescent Idiopathic Scoliosis Using the Simplified Skeletal Maturity System

Spine Deform. 2019 Nov;7(6):890-898.e4. doi: 10.1016/j.jspd.2019.01.011.


Study design: Prognostic study and validation using prospective clinical trial data.

Objective: To derive and validate a model predicting curve progression to ≥45° before skeletal maturity in untreated patients with adolescent idiopathic scoliosis (AIS).

Summary of background data: Studies have linked the natural history of AIS with characteristics such as sex, skeletal maturity, curve magnitude, and pattern. The Simplified Skeletal Maturity Scoring System may be of particular prognostic utility for the study of curve progression. The reliability of the system has been addressed; however, its value as a prognostic marker for the outcomes of AIS has not. The BrAIST trial followed a sample of untreated AIS patients from enrollment to skeletal maturity, providing a rare source of prospective data for prognostic modeling.

Methods: The development sample included 115 untreated BrAIST participants. Logistic regression was used to predict curve progression to ≥45° (or surgery) before skeletal maturity. Predictors included the Cobb angle, age, sex, curve type, triradiate cartilage, and skeletal maturity stage (SMS). Internal and external validity was evaluated using jackknifed samples of the BrAIST data set and an independent cohort (n = 152). Indices of discrimination and calibration were estimated. A risk classification was created and the accuracy evaluated via the positive (PPV) and negative predictive values (NPV).

Results: The final model included the SMS, Cobb angle, and curve type. The model demonstrated strong discrimination (c-statistics 0.89-0.91) and calibration in all data sets. The classification system resulted in PPVs of 0.71-0.72 and NPVs of 0.85-0.93.

Conclusions: This study provides the first rigorously validated model predicting a short-term outcome of untreated AIS. The resultant estimates can serve two important functions: 1) setting benchmarks for comparative effectiveness studies and 2) most importantly, providing clinicians and families with individual risk estimates to guide treatment decisions.

Level of evidence: Level 1, prognostic.

Keywords: Adolescent idiopathic scoliosis; Curve progression; External validation; Internal validation; Natural history; Prognostic model.

Publication types

  • Clinical Trial
  • Comparative Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Braces / standards*
  • Braces / statistics & numerical data
  • Child
  • Disease Progression
  • Female
  • Humans
  • Male
  • Musculoskeletal Development / physiology*
  • Musculoskeletal System / diagnostic imaging*
  • Predictive Value of Tests
  • Prognosis
  • Prospective Studies
  • Radiography / methods
  • Reproducibility of Results
  • Risk Assessment / methods
  • Scoliosis / diagnostic imaging
  • Scoliosis / therapy*
  • Spinal Curvatures / classification
  • Spinal Curvatures / diagnostic imaging*