Curve Progression After the Termination of Bracing for Adolescent Idiopathic Scoliosis: Usefulness of Combining the Proximal Femur Maturity Index (PFMI) and Risser Staging

Background
The brace therapy for adolescent idiopathic scoliosis (AIS) typically ends upon the end of growth. However, determining the timing of growth cessation can be challenging. The purpose of this study was to evaluate the utility of the proximal femur maturity index (PFMI), which can be assessed simultaneously with Risser staging without requiring additional radiation exposure, in determining the appropriate timing to terminate bracing. To achieve this, we investigated the relationship between skeletal maturity at the end of bracing, post-bracing curve progression, and height growth in patients who had been successfully treated with a brace.
Methods
Between April 2010 and March 2021, a total of 84 female patients with AIS who started bracing at our hospital with an initial Cobb angle of 20-40 degrees were included. All patients were followed for at least one year after brace termination. Height and radiographic parameters (Risser staging, PFMI, Cobb angle) were retrospectively collected.
Results
At the end of the bracing period, patients were categorized into Risser stage 4 (85.7%) and 5 (14.3%). By the last follow-up, patients with Risser stage 4 experienced an average main curve progression of 1.8°, whereas those with Risser stage 5 had an average progression of −0.3° (P = 0.03). Patients with Risser stage 4 were further divided into PFMI grade 5 (59.7%) and 6 (40.3%). Significant curve progression was observed in patients with PFMI grade 5 (average: 3.0°) compared to grade 6 (average: -0.6°) (P < 0.0001). The mean height growth was 1.9 cm/year for PFMI grade 5, and 0.3 cm/year for grade 6, with significant differences between these groups (P < 0.001).
Conclusions
PFMI allowed further categorization within Risser stage 4: PFMI grade 5 indicated remaining growth potential and risk of postbracing curve progression, whereas grade 6 indicated growth cessation. The combined use of Risser staging and PFMI, both evaluable through the same whole-spine radiograph, may provide a more accurate prediction of growth cessation.