Analysis of the mechanisms of idiopathic scoliosis progression using finite element simulation.

The mechanisms of idiopathic scoliosis progression are still not fully understood. The aim of this study is to explore, using finite element simulation, effect of the combination of gravity and anterior spinal overgrowth on scoliosis progression. 14 adolescents (10 girls, 4 boys) with an average age of 10.8 years [range 9; 13] were divided in three groups: thoraco-lumbar scoliosis (TL), lumbar scoliosis (L), asymptomatic patients (A). Accurate 3D reconstructions of the spine have been built using bi-planar X-rays. A patient specific validated finite element model has been used. Simulations have been launched with simulation of the combined effect of gravity and growth. The progression during the simulation was defined by a maximal axial rotation movement greater or equal than 4 degrees and a maximal lateral displacement greater or equal than 5 mm ("first order progression" for one criterion, "second order" for the both criteria). In the group TL, we notice an aggravation for 4 patients (Cobb angle increase at least by 4 degrees , mean at 5.9 degrees ). Only three patients of the group L show a progression with a smaller Cobb angle increase (mean 3.9 degrees ). For the group A, no progression is found for 3 and a progression is found for 1. An anterior spinal overgrowth combined with gravity and a pre-existent curve in the spine could lead to a progression of scoliosis. It seems necessary to consider differently lumbar curves from other curves. Numerical simulation with a patient specific model appears as a useful tool to investigate mechanisms of scoliosis aggravation.