Moderate scoliosis continues to progress at 30-year follow-up: a call for concern?

Purpose This natural history study reports long-term radiographic and clinical outcomes of patients with diagnosis of AIS with curves between 30° and 50°. Our purpose was to determine if any intervention in the natural history is warranted. Methods This was a longitudinal descriptive study at a single institution. We reviewed patient factors, radiographic parameters, and patient-reported outcomes at 20- and 30-year follow-up. Results A total of 31 patients were included. At skeletal maturity (which was the initial point of measurement), the median age was 17 years (range 12–21), the thoracic Cobb angle was 35° ± 5° (maximum–minimum 27°–47°), and the lumbar Cobb angle was 33° ± 7° (maximum–minimum 18°–45°). The median final follow-up was 35 years (median age 52, range 32–61) when the thoracic Cobb angle was 47° ± 12° (maximum–minimum 31°–74°) and the lumbar Cobb angle was 40° ± 17° (maximum–minimum 19°–69°). At final follow-up, 9 (29%) patients had a structural curve > 50°. Ten (32%) patients had a curve from 40° to 49° and 11 (35%) patients had a curve < 40°. The thoracic Cobb angle had progressed from < 40° to > 50° in 5 patients. Thoracolumbar and lumbar Cobb angles progressed from < 40° to greater than > 50° in 1 and 3 patients, respectively. Few patients had functional limitations according to Roland–Morris, Oswestry, and SF36 scores. Pain scores were minimal at final follow-up. Conclusion All AIS curves between 30° and 50° at skeletal maturity tend to progress. Thoracic curves progress more than lumbar curves during the first 20 years and then progression slows down. The opposite happens with lumbar curves. Therefore, the rate of progression decreases with thoracic curves and increases with lumbar curves. Nevertheless, few patients have functional limitations. Further follow-up is necessary to define the true long-term outcome of moderate curves at maturity.