Biomechanical analysis of the impact of increasing levels of body mass index on the ability of a bracing orthosis to alter the asymmetric compressive growth plate loading in a scoliotic spine

Abstract

BackgroundThe impact of increasing body mass index (BMI) on the magnitude of alterations in the asymmetric compressive vertebral growth plate loading of a scoliotic spine following 50% in-brace correction is studied using the finite element method, and subsequent alteration of the longitudinal bone growth rate is quantified. MethodsUpper body weight loading corresponding to a single patient spine geometry representing 4 BMI classifications – overweight (BMI = 25 kg/m2), and class-1, -2, and -3 obesity (BMI – 30 kg/m2, 35 kg/m2, and 40 kg/m2, respectively) – is applied to a three-dimensional finite element model (FEM) of the human thoracolumbosacral spine. The FEM represents a Lenke 1AN scoliotic curve type with 30-degree Cobb angle and 10-degree apical vertebral rotation. Bracing simulation is performed until 50% in-brace correction is achieved. Changes in bending moment at each motion segment and on each growth plate after bracing is simulated and compared between each BMI level. FindingsAs BMI increases, the average magnitude of change in bending moment on each growth plate following bracing decreases. For BMIs 30 kg/m2, 35 kg/m2, and 40 kg/m2, the average change in bending moment on each vertebral growth plate following 50% in-brace correction is 31% smaller (P = .00006), 60% smaller (P = .00007), and 96% smaller (P = .00006), respectively, than for BMI 25 kg/m2. InterpretationsResults indicate that BMI significantly impacts the ability of a bracing orthosis to alter the asymmetric compressive growth plate loading in a scoliotic spine, which is the design function of bracing. This suggests that increasing BMI may significantly impact the ability of a bracing orthosis to halt curve progression in a scoliotic patient.