Finite element simulation of growth modulation during brace treatment of adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS) is a spine deformity whose progression during growth is affected by asymmetrical loads acting on the spine. The conservative brace treatment aims to limit the deformity's progression until the end of skeletal growth. This study's objective was to develop a patient-specific finite element model (FEM) simulating immediate in-brace (IB) correction and subsequent growth modulation over 2 years of treatment. Thirty-five retrospective AIS cases with documented correction over 2 years were analyzed. For each case, a patient-specific FEM was built and IB correction was simulated. Vertebral growth and its modulation were modeled using simulated pressures on epiphyseal vertebral growth plates, including a compliance factor representing the recorded brace wear. The simulated Cobb angles, thoracic kyphosis, lumbar lordosis, and apical vertebral rotation were compared with the actual measurements immediately IB and out-of-brace (OOB) at the 2-year follow-up. Treatment outcomes according to simulated compliance scenarios of no brace-wear versus full brace-wear were also computed. The average immediate IB difference between the simulated and actual Cobb angle was 4.9° (main thoracic [MT]) and 3.7° (thoraco-lumbar/lumbar [TL/L]). Two-year OOB, it was 5.6° (MT) and 5.4° (TL/L). The no brace-wear and full brace-wear compliance scenarios resulted respectively in 15/35 (43%) and 31/35 (89%) simulated spine deformities progressing by <5° over 2 years of treatment. Clinical significance: the FEM's ability to simulate the final correction with an accuracy on the order of the radiological measurements' interoperator reproducibility, combined with its sensitivity to brace-wear compliance, provides confidence in the model's predictions for a comparative context of use like improving a brace's design before its application.