Dynamic spasticity of plantar flexor muscles in cerebral palsy gait

Area of Science:

• Biomechanics
• Neuroscience
• Pediatric Rehabilitation

Background:

• Cerebral palsy (CP) is a common neurodevelopmental disorder.
• Spasticity, a hallmark of CP, affects muscle tone and movement.
• Dynamic spasticity, the velocity-dependent increase in muscle tone, is crucial during gait but poorly quantified in pediatric CP.

Purpose of the Study:

• To quantify dynamic spasticity in the gastrocnemius and soleus muscles during gait in children with spastic cerebral palsy.
• To investigate the relationship between muscle-tendon stretch velocity and muscle activity across different walking speeds.

Main Methods:

• A prospective, cross-sectional study involving 17 children with spastic CP and 11 typically developing controls.
• Three-dimensional kinematic and electromyographic data were collected during walking at three different speeds.
• Musculoskeletal modeling was used to calculate muscle-tendon velocities of the gastrocnemius medialis and soleus.

Main Results:

• Spastic calf muscles demonstrated a significantly higher coupling between muscle-tendon stretch velocity and muscle activity during the swing phase compared to controls (approximately 4 times higher).
• This dynamic spasticity effect increased with walking speed in children with CP.
• In the stance phase, spastic muscles showed rapid stretching during loading response, but pre-existing muscle activity from the swing phase obscured a clear dynamic spasticity effect.

Conclusions:

• Children with spastic cerebral palsy exhibit heightened dynamic spasticity in their calf muscles, characterized by an increased coupling between muscle-tendon stretch velocity and muscle activity.
• This phenomenon is most pronounced during the swing phase of gait and is exacerbated by increased walking speed.
• Understanding dynamic spasticity is critical for developing targeted interventions for gait impairments in pediatric CP.