Longitudinal interaction between muscle impairments and gait pathology in growing children with Duchenne muscular dystrophy.

Background: Children with Duchenne muscular dystrophy (DMD) present with progressive gait pathology due to progressive muscle weakness and contractures. However, the associations between specific muscle impairments and specific gait features have never been quantified. Therefore, the aim of this longitudinal observational cohort study was to investigate the longitudinal interaction between progressive muscle impairments and progressive gait pathology in growing boys with DMD.

Methods: Thirty-one boys with DMD (aged 4.6-16.4 years) were repeatedly measured between 2015 and 2022, resulting in a total dataset of 152 observations. Fixed dynamometry, goniometry and 3D gait analysis were used to assess lower limb muscle weakness, passive range of motion and gait. Joint random-effect models between gait and muscle outcomes were fitted. The correlation between the random intercepts (r_a) and random slopes (r_b) indicated the relationship between the initial values and progression rates over time of two outcomes, respectively.

Results: Specific muscle impairments were related to specific gait features, both in terms of initial values (r_a=0.470-0.757; p < 0.029) and progression rates (r_b=0.547-0.812; p < 0.024). Decreased hip extension strength was associated with increased maximal posterior trunk angle (r_b=-0.588; p = 0.0004), increased maximal anterior pelvic tilt angle (r_a=-0.543; p = 0.0040 and r_b=-0.812; p < 0.0001), and reduced maximal hip extension moment (r_a=0.536; p = 0.0289). Decreased hip abduction strength was associated with increased step width (r_a=-0.549; p = 0.0021) and increased maximal internal foot progression angle (r_b=-0.547; p = 0.0117). Decreased knee extension strength was associated with reduced maximal knee extension moment (r_a=0.702; p < 0.0001), reduced maximal knee power absorption (r_a=0.757; p < 0.0001), and reduced dorsiflexion angle at initial contact (r_b=0.684; p = 0.0237). Decreased dorsiflexion range of motion was associated with reduced dorsiflexion angle at initial contact (r_a=0.732; p < 0.0001 and r_b=0.627; p = 0.0202) and reduced maximal dorsiflexion angle in swing (r_a=0.663; p < 0.0001).

Conclusion: This is the first study that objectively quantified the longitudinal interaction between muscle impairments and gait features, providing valuable insights into the underlying mechanisms of pathological gait in DMD. The observed associations highlight the importance of targeted clinical assessments. These findings offer a foundation for optimizing rehabilitation strategies, orthotic management, and orthopedic interventions, ultimately improving clinical decision-making and enhancing mobility outcomes in children with DMD.