Neural Prostheses and Gait Performance: Model-Based Strategies

The study aims to find the optimal patterns of functional electrical stimulation (FES) of
muscles in the lower legs that will improve walking ability in those who have had a stroke
and at the same time ensure walking stability will be achieved through an analytical
approach comprised of computational models and gait simulations to objectively determine
patient-specific patterns of muscle activation. The investigators will develop a computer
simulation of the dynamics of hemiplegic gait characterized by unilateral plantarflexor
weakness. Then, the investigators will relate the results of the computer model results to
real data collected from subjects with known plantarflexor weakness to provide a theoretical
basis for improving gait efficiency and stability with FES.

Inclusion Criteria:

This study includes stroke survivors greater than 18 years of age, >180 days from first
clinical hemorrhagic or nonhemorrhagic stroke with:

- Unilateral hemiparesis with sufficient endurance and motor ability to ambulate >30
feet continuously without an AFO requiring no more than 25% physical help

- Berg Balance Scale score >23 without assistive devices

- Standing ankle dorsiflexion strength of <4/5

- Foot-drop during ambulation with gait instability or inefficient gait defined as
supervision need

- Possible use of physical assistance or assistive device (cane, walker)

- Evidence of foot-drop as seen by "dragging" or "catching" of affected toes during
limb swing or circumducting affected limb

- Vaulting of the unaffected limb or hiking the affected hip to clear toes.

- Intact and electrically ex-citable lower motor neurons

- Ankle dorsiflexion to at least neutral while standing with electrical stimulation of
common peroneal and tibial nerves without painful hypersensitivity to stimulation

- Adequate social support and stability

- Medically stable with intact skin in affected lower limb

- Willingness to comply during research procedures

- No systemic co-morbidities

- No history of potentially fatal cardiac arrhythmias i.e. ventricular tachycardia,
supraventricular tachycardia and rapid ventricular response atrial fibrillation with
hemodynamic instability

- No psychological problems or chemical dependency

- No acute medical complications such as depression or chronic anxiety requiring long
term pharmacological therapy. Able-bodied controls must be of similar age, body mass
and stature as those with hemiparesis and must be free of any medical and disabling
orthopedic problems.

Exclusion Criteria:

In addition to failure to meet the inclusion criteria, participants will be excluded from
the study for the following:

- Requires an AFO to prevent knee flexion collapse in stance

- Excessive edema of affected extremity

- Absent sensation in affected limb

- History of potentially fatal cardiac arrhythmias such as ventricular tachycardia,
supraventricular tachycardia, and rapid ventricular response, atrial fibrillation
with hemodynamic instability

- Demand pacemakers or any implanted electronic systems

- Pregnancy

- Uncontrolled seizure disorder

- Ipsilateral lower limb lower motor neuron lesion

- Parkinson's disease

- Spinal cord injury

- Traumatic brain injury

- Multiple sclerosis

- Ankle plantar flexor contraction

- Severely impaired cognition and communication

- Painful hypersensitivity to neuromuscular stimulation of common peroneal nerve

- Knee hyperextension (genu recurvatum) that cannot be adequately corrected with
peroneal nerve stimulation

- History of botulinum toxin to the lower extremity within the prior three months.