Background and purpose — Data on effectiveness of nighttime bracing compared with full-time bracing in ado-lescent idiopathic scoliosis is scarce. We aimed to investigate risk of curve progression and surgery with nighttime bracing vs full-time bracing for patients with moderate-grade adolescent idiopathic scoliosis.

Methods — Skeletally immature individuals with idio-pathic scoliosis (25°–40°) treated with a nighttime brace as part of a parallel-group randomized controlled trial (RCT) were compared with non-participants treated with a full-time brace. In the case of curve progression of more than 6° in the nighttime brace group individuals were offered transition to a full-time brace. Surgery was offered if curve sizes were 45° or larger.

Results — Median age at treatment start was 12.8 years (nighttime brace n = 45, full-time brace n = 44). Female sex (odds ratio [OR] 6.5, 95% confidence interval [CI] 1.1–37.4), lower Risser grade (OR 1.6, CI 1.01–2.7), and larger curve size at the beginning of brace treatment (OR 1.4, CI 1.2–1.5) increased the risk of curve progression to ≥ 45°. Major curves in the groups were similar at median 33 months’ follow-up (P = 0.7). After 94 months of follow-up, 11 patients in the nighttime brace group and 6 in the full-time brace group had undergone surgery (OR 2.0, CI 0.7–6.1).

Conclusion —Nighttime bracing, including a possibility to transition to full-time brace in the case of progression, dem-onstrated comparable effectiveness in preventing curve pro-gression, but a tendency to a higher risk of surgical treatment.