Simulation of progressive spinal deformities in Duchenne muscular dystrophy using a biomechanical model integrating muscles and vertebral growth modulation

Abstract

Ninety percent of Duchenne muscular dystrophy patients develop scoliosis in parallel with evident muscular and structural impairment. Altered muscular spinal loads acting on growing vertebrae are likely to promote a self-sustaining spinal deformation process. The purpose of this study was to simulate the effect of asymmetrical fat infiltration of the erector spinae muscles combined with vertebral growth modulation over a period of growth spurt. A finite element model of the trunk was built. It integrates (1) longitudinal growth of vertebral bodies and its modulation due to mechanical stresses, (2) muscles and control processes generating muscle recruitment and forces. Three different impairments of the erector spinae muscles were considered and their actions over 12 consecutive cycles representing a span of 12 months were analyzed. When asymmetrical muscle degeneration was simulated and weaker erector spinae muscles were located on the convex side of the curve, mild scoliosis (Cobb angle of 8-19 degrees ) was induced in the frontal plane and the kyphosis increased from 72 degrees to 110 degrees in all simulations. Those changes were accompanied by a substantial increase of muscle activity in the Rectus Abdominus and Obliquus Internus. Scoliosis as documented in the literature were induced through an asymmetrical activity in the erector spinae muscles and it can be hypothesized that the Rectus Abdominus and Obliquus Internus have a role in maintaining balance and counteracting against spine torsion. This study demonstrated the feasibility of the modeling approach to investigate a musculo-skeletal deformation process based on a neuromuscular deficit.