Factors Related to Curve Progression in Adolescent Idiopathic Scoliosis Girls at Skeletal Maturity

<b>Background/Objectives</b>: 45-50° is typically considered a threshold to offer surgical intervention for adolescent idiopathic scoliosis (AIS) patients. Larger curves may continue to progress even after skeletal maturity (SM), but the risk of this progression remains poorly defined. This study aimed to quantify the risk factors for continued curve progression in skeletally mature females with moderate curves (25° to 45°). <b>Methods</b>: We reviewed a Non-Operative AIS Database of >2300 patients with curves of 25° to 45° at radiographic SM (defined as United States Risser 4 and Sanders 7, or Risser 5) and follow-up >24 months after SM. Progression of >5° and progression to 50° were analyzed using chi-squared tests and Mann-Whitney U tests to detect differences in factors at SM. <b>Results</b>: 90 patients met the inclusion criteria. For various starting curve sizes at SM, progression > 5° was 7.1% (25°), 26.7% (30°), 22.2% (35°), 42.3% (40°), and 33.3% (45°), respectively. Progression to 50° was 0% (25°), 0% (30°), 11.1% (35°), 42.3% (40°), and 55.6% (45°). Progression > 5° was higher in patients with Risser 4 at SM versus Risser 5 (<i>p</i> = 0.04), when curves were >35° at SM (<i>p</i> = 0.04), and onset of menarche was <16 months before SM (<i>p</i> = 0.03). Progression to 50° was higher for curves > 40° at SM (<i>p</i> < 0.00001) and when the onset of menarche was <15 months before SM (<i>p</i> = 0.02). <b>Conclusions</b>: Curves of 25° to 45° at SM can still progress > 5°, and curves of 35° to 45° can still progress to 50°. Patients should be counseled regarding these risks so they can make informed decisions about appropriate monitoring and treatment.