Control of paraplegic ankle joint stiffness using FES while standing

Area of Science:

• Biomedical Engineering
• Rehabilitation Technology
• Neuroscience

Background:

• Maintaining upright posture is challenging for individuals with paraplegia.
• Functional electrical stimulation (FES) offers a potential solution for restoring motor function.
• Ankle stiffness control is crucial for dynamic balance during standing.

Purpose of the Study:

• To investigate the feasibility of controlling ankle stiffness using FES in standing individuals.
• To assess the effectiveness of FES-based ankle stiffness control for balance in paraplegia.
• To develop feedback systems for enhancing balance control in paraplegia.

Main Methods:

• Subjects stood with ankles braced, receiving ankle moment via FES of flexor and extensor muscles.
• A feedback control strategy regulated ankle moment based on desired stiffness and measured ankle angle.
• Two subjects (one neurologically intact, one paraplegic) participated.

Main Results:

• Plantarflexor stimulation achieved high ankle moments (up to 60 Nm) with accurate tracking, enabling good stiffness control during forward lean.
• Dorsiflexor stimulation produced lower moments (up to 15 Nm), leading to saturation and poor stiffness control during backward lean.
• Higher desired stiffness required greater external force to perturb posture.

Conclusions:

• Controlled FES can achieve accurate ankle stiffness control within muscle strength limitations.
• FES-based ankle stiffness control has potential to aid upright posture stabilization in paraplegia.
• This technology may facilitate balance by applying additional upper-body forces.