Modified Lenke Classification Stratifies Brace Initiation Risk and Longitudinal Cobb Angles Trajectories in Female Patients With Adolescent Idiopathic Scoliosis.

OBJECTIVE: To determine whether baseline modified Lenke classification (MLC), assessed from standing whole-spine radiographs, stratifies brace initiation risk and longitudinal Cobb-angle trajectories in female patients with adolescent idiopathic scoliosis (AIS) before reaching the conventional bracing threshold.

SUMMARY OF BACKGROUND DATA: AIS progression is heterogeneous. Baseline Cobb angle and skeletal maturity are established risk factors, but whether simple baseline curve-pattern classification adds risk-stratification information during nonoperative follow-up remains unclear.

METHODS: We included female AIS patients aged 10 to <18 years with a baseline maximum Cobb angle ≥10° and <25°. Patients with prior brace treatment, brace initiation at the first visit, insufficient pre-brace follow-up, or missing baseline variables were excluded. The primary outcome was brace initiation. Brace-free survival was assessed using Kaplan-Meier analysis and multivariable Cox models adjusted for baseline maximum Cobb angle, age, body mass index, menarche status, and Risser status. Model fit was compared between a conventional baseline model and a model additionally including MLC. Two-year risks were estimated at fixed baseline Cobb angles. Longitudinal trajectories were analyzed using a linear mixed-effects model with natural cubic splines, an age-by-MLC interaction, and patient-specific random intercepts and slopes for age.

RESULTS: A total of 1087 patients were included; 210 (19.3%) underwent brace initiation. Brace-free survival differed across MLC groups. In multivariable Cox analysis, MLC 2, 3, 4, and 6 showed higher hazards of brace initiation than MLC 1, with the highest risk in MLC 4. Adding MLC improved likelihood-based model fit (χ²=19.35, df=5, P=0.002) and reduced AICc, although BIC increased. At baseline Cobb 20°, adjusted 2-year risk ranged from 23.3% in MLC 1 to 55.9% in MLC 4. Longitudinal Cobb-angle trajectories differed according to MLC.

CONCLUSION: Baseline MLC may provide complementary information for stratifying brace-initiation risk and longitudinal Cobb-angle trajectories before the conventional bracing threshold.

STUDY DESIGN: Retrospective single-center cohort study.