Ankle Robot to Reduce Foot Drop in Stroke

Deficits in ankle control after stroke can lead to foot drop, resulting in inefficient, aberrant gait and an elevated falls risk. Using a novel ankle robot and newly invented adaptive control system, this study tests whether robotic-assisted treadmill training will improve gait and balance functions in chronic stroke survivors with foot drop impairment. It is hypothesized that, compared to treadmill training alone, integrating adaptive ankle robotics with treadmill training will reduce drop foot during independent overground walking, resulting in greater mobility, improved postural control, and reduced fall risk.

This proposal investigates a novel ankle robot (anklebot) adaptive control approach integrated with treadmill training to reduce foot drop and improve mobility function in chronic hemiparetic stroke survivors. Currently, stroke survivors with foot drop are trained to live with a cane or other assistive device, and often ankle foot orthotics (AFOs) for safety. Neither mediates task-practice or neuromotor recovery.

The investigators have developed an adaptive anklebot controller that detects gait cycle sub-events for precise timing of graded robotics assistance to enable deficit severity-adjusted ankle motor learning in the context of walking. The investigators' pilot findings show that 6 weeks treadmill training with anklebot (TMR) timed to assist swing phase dorsiflexion only is more effective than treadmill alone (TM) to improve free-walking swing dorsiflexion at foot strike, floor-walking speed, and the benefits are retained at 6 weeks post-training. Notably, swing-phase TMR training improved paretic leg push-off, and reduced center-of-pressure sway on standing balance, indicating potential benefits to other elements of gait and balance, beyond those robotically targeted toward foot drop.

This randomized study investigates the hypothesis that 6 weeks TMR is more effective to improve durably gait biomechanics, static, and dynamic balance, and mobility function in chronic stroke survivors with dorsiflexion deficits, compared to TM alone. Aims are to determine the compare effectiveness of 6 weeks TMR vs. TM alone on:

1. Independent gait function indexed by gait velocity, swing-phase DF (dorsiflexion), terminal stance push-off.
2. Balance function indexed by measures of postural sway (CoP), asymmetric loading in quiet standing, peak paretic A-P forces in non-paretic gait initiation, and standardized scales for balance and fall risk.
3. Long-term mobility outcomes, assessed by repeated measures of all key gait and balance outcomes at 6 weeks and 3 months after formal training cessation.

Eligibility Criteria:
Inclusion Criteria:

* Ischemic or hemorrhagic stroke \> 2 months prior in men or women
* Residual hemiparesis of the lower extremity that includes symptoms of foot drop
* Capable of ambulating on a treadmill with handrail support
* Already completed all conventional physical therapy
* Adequate language and cognitive function to provide informed consent and participate in testing and training

Exclusion Criteria:

* Cardiac history of:

  * Unstable angina
  * Recent (\< 3 months) myocardial infarction
  * Congestive heart failure (NYHA category II or higher)
  * Hemodynamic valvular dysfunction
  * Hypertension that is a contraindication for a bout of treadmill training (\>160/100 mmHg on two assessments)
* Medical history of:

  * Recent hospitalization (\< 3 months) for any serious condition leading to significant bed-rest or reduction in mobility function
  * Symptomatic peripheral arterial occlusive disease
  * Orthopedic or chronic pain conditions restricting exercise
  * Pulmonary failure requiring oxygen
  * Uncompensated renal failure
  * Active cancer
* Neurological history and exam consistent with:

  * Dementia
  * Receptive or global aphasia that confounds testing and training, operationally defined as unable to follow 2-point commands
  * Non-stroke neurological disorder restricting exercise (e.g. Parkinson's Syndrome, myopathy)
  * Untreated major depression