Muscle weakness but also contractures contribute to the progressive gait pathology in children with Duchenne muscular...

Muscle weakness and contractures cause gait deficits in children with Duchenne muscular dystrophy (DMD) but their relative contributions are poorly understood and hence it is unclear whether contractures should be treated. Therefore, we aimed to differentiate the effect of muscle weakness in isolation from weakness and contractures combined on the gait patterns.

We used computer simulations that generate gait patterns based on a musculoskeletal model (without relying on experimental data) to establish the relationship between muscle impairments and gait deviations. We previously collected a longitudinal database of 137 repeated measurements in 30 boys with DMD and found that the data measured through 3D gait analysis could be clustered in three gait patterns. We estimated weakness based on data from fixed dynamometry, and contractures based on goniometry and clinical measures. Foot deformities were modeled by reducing the height of all foot segments and decreasing the strength of the intrinsic foot muscles. We created musculoskeletal models that either represented (1) the mean weakness; (2) the mean weakness and contractures; or (3) the mean weakness, contractures and foot deformities, in each gait pattern.

Simulations based on models with both weakness and contractures captured most (but not all) experimentally observed gait deviations, demonstrating the validity of our approach. While muscle weakness was primarily responsible for gait deviations, muscle contractures and foot deformities further contributed to gait deviations. Interestingly, the simulations predict that the combination of increasing weakness and contractures rather than increasing weakness alone causes loss of ambulation for the most affected gait pattern.

Predictive simulations have the potential to elucidate causal relationships between muscle impairments and gait deviations in boys with DMD. In the future, they could be used to design targeted interventions (e.g. stretching, assistive devices) to prolong ambulation.