Étude biomécanique des déformations rachidiennes dans la dystrophie musculaire de Duchenne

Duchenne muscular dystrophy (DMD) is the most common form of muscular dystrophy.

This thesis is a continuation of Sainte-Justine Hospital and École Polytechique de Montréal research activities on scoliosis. This project aims at studying the spinal deformities that specifically develop in DMD disorder and encloses two complementary clinical and biomechanical sections. The clinical section evaluates the impact of deflazacort treatment on the scoliotic deformities in teenagers. The second section develops a finite element model of growth, growth modulation, muscles and motor control and studies possible pathomechanisms involved in progressive spinal deformities in DMD. The specific objectives of this thesis were to: (1) determine if the deflazacort treatment has modified the prevalence, the severity of the spinal deformities and/or the curve patterns, in comparison to series reported before the recent advent of drug therapy in this disorder; (2) develop a finite element model of the trunk integrating vertebral growth and growth modulation as well as the muscles and the control process generating muscle recruitment and forces; (3) investigate, with the developed finite element model, two features that could be implicated in the proposed pathogenesis hypotheses: (a) asymmetrical fat infiltration of trunk muscles, (b) growth parameters following a deflazacort treatment.

The medical and radiographic charts of 60 patients with DMD followed at a paediatric neuromuscular clinic were reviewed retrospectively. The prevalence of scoliotic deformities was 49% in the patients treated with deflazacort, which is considerably lower than the one reported before the advent of corticosteroid therapy (90%). The severity of scoliotic deformities was much lower than the ones described in previously reported historical series. Curve patterns were different than the ones reported in the natural history as only one C-shape curve pattern with pelvic obliquity, typical of neuromuscular scoliosis was found. Incidence of kyphosis and pelvic obliquity was very low, which is also in contrast with previously reported cohorts. The study in this thesis was not able to determine if deflazacort definitely halts the progression of scoliosis or if it only slows down its progression.

In the second section of this thesis, modeling of vertebral growth and growth modulation was combined to muscles and control process generating muscle recruitment and forces. With this finite element model, asymmetrical loading from the erector spinae muscles were studied and spinal configurations evolving from group I to II of Gibson & Wilkins classification were reproduced. (Abstract shortened by UMI.)