Study design: Prospective cohort study.
Objectives: The objective of this study was to examine intermediate-term progression for a large series of patients with adolescent idiopathic scoliosis (AIS) with curves 40° or greater.
Background: Curve progression in AIS has been well documented for smaller curves in adolescence up to skeletal maturity; however, the data on curve progression past 40° or into adulthood are limited. With many surgeons recommending surgical correction when patients reach this threshold, it is important to understand the radiographic progression of curves into adulthood.
Methods: A database of all patients seen by a single surgeon from 1984 through 2018 with AIS curves progressing to at least 40° entered prospectively was utilized for this study. This included a total of 738 patients. Curve progression was analyzed overall and stratified by length of follow-up, curve location, and Risser stage at the time of presentation among other variables. Curve magnitude and Risser stage designations in this study were validated by performing a separate inter- and intrarater agreement study using four independent reviewers reading 50 patients' Cobb angle and Risser stage blinded in triplicate to examine the reliability of the study measurements.
Results: Annualized curve progression (ACP) averaged 6.3 ± 10.4°. ACP varied with length of follow-up: patients with up to 1 year of follow-up had an average ACP of 11.5 ± 17.0°, while those with 1-2 years had 8.2 ± 8.8°, and 2-5 years had 3.7 ± 4.1°, tapering off further from there. Risser stage 0 or 1 was associated with the highest ACP as compared to Risser stage 2-3 or 4-5. Intraclass correlation (ICC) values for Cobb angle measurement and Risser stage designations from four raters measuring 50 patients' measures, blinded and in triplicate, were all > 0.80, signifying a high degree of reliability within and between readers.
Conclusions: Annualized curve progression for 40° and greater curves was not linear over time; it was greatest immediately after a curve reaches 40° and tapered off over the next decade. Immature Risser stage at presentation was strongly associated with increasing ACP at all time frames.
Level of evidence: Prognostic Level I.
Keywords: Adolescent idiopathic scoliosis; Curve progression; Natural history.