Active Limb Orthosis for Home-Use Stroke Hemiparetic Gait Rehabilitation

Hemiparesis and other impairments are a frequent and disabling consequence of stroke and can
lead to asymmetric and inefficient walking patterns. Training on a split-belt treadmill,
which has two separate treads driving each leg at a different speed, can correct gait
asymmetries post-stroke. However, the effects of split-belt treadmill training only partially
transfer to everyday walking over ground and extended training sessions are required to
achieve long-lasting effects. Our previous studies suggest that the iStride device that has
been developed in our laboratory can be used as an alternative gait training device for
people with stroke. The iStride device mimics the actions of the split-belt treadmill, but
can be used during over-ground walking and in one's own home, thus enabling long-term
training. The iStride device does not require any external power and is completely passive;
all necessary forces are redirected from the natural forces present during walking since it
utilizes the wearer's weight to generate its movements. While the movements of the iStride
device are similar to the split belt treadmill, and the iStride device generates a similar
aftereffect, the efficacy of this shoe in modifying the gait of an individual with stroke is
not yet verified. This research aims to continue to test the iStride device on individuals
with stroke to determine if the related effects in a clinic setting, are also beneficial and
safe in a home environment.

In this study, we will test the efficacy of the iStride device on individuals with stroke in
the clinic and within their own home. Efficacy will be evaluated based on the change in gait
coordination and also based on subjects' self-reported comfort on the device. We predict that
the iStride device will result in changes to interlimb coordination of gait and prove to be a
safe and effective device to be used in ones' home.

The asymmetric nature of hemiparetic gait can have a large impact on functional walking
ability. For example, swing phase asymmetry is a significant predictor of hemiparetic walking
performance because it strongly correlates with stages of motor recovery, walking speed, and
falls. Another measure of temporal asymmetry - double support duration - is similarly
correlated with walking speed. In addition, spatial (e.g. step length) asymmetry is
associated with decreased propulsive force on the paretic leg, which limits forward motion of
the body and reduces gait efficiency. The importance of gait efficiency should not be
understated - the elevated energy demands of hemiparetic gait combined with physical
deconditioning post-stroke can greatly limit performance of activities of daily living,
contributing to poor cardiovascular fitness and metabolic syndrome. In turn, this can
increase the risks of a second stroke or cardiovascular event and is associated with
increased morbidity and mortality rates. Therefore, improving gait symmetry should be an
important goal for therapy, to not only improve functional mobility and reduce injury, but
also to enhance general health and well-being post-stroke.

Practicing walking on a split-belt treadmill can correct abnormal interlimb coordination of
gait in individuals with hemiparesis following stroke or other central nervous system
lesions. Asymmetric gait can manifest as a spatial asymmetry, in which steps taken on one
side are longer than those on the other. It can also manifest as a temporal asymmetry, where
the timing is uneven on the paretic and non-paretic sides. Temporal asymmetries are often
measured as differences in the duration of double support periods, which are the amount of
time both feet are simultaneously contacting the ground and are measured separately for the
paretic and non-paretic sides. The iStride device is designed to cause changes in both
spatial and temporal gait symmetry. We predict that the iStride device would cause the steps
on the side with the iStride device to be larger since individuals would compensate for the
backward rolling motion by placing their foot farther forward in stance, thus increasing the
distance between the two feet. Similarly, since the stride is longer, it may also shorten the
duration of stance relative to the other side. With shortened stance duration, the amount of
time spent in double-support at the end of stance would likely decrease as well.

Although the original idea of the iStride device is derived from the motion of the
split-belt-treadmill, there are distinct differences between walking on the device and
walking on a split-belt treadmill with asymmetric belt velocities. While the body's velocity
relative to ground is zero on a split-belt treadmill, the relative velocity of the iStride
device is non-zero and forward. The device forces the wearer's foot forward or backward
whereas the treadmill moves both feet backward, but at different speeds. For both the
split-belt treadmill and the iStride device, the relative velocity between both feet is
similar and the backward-moving iStride device takes the place of the faster tread.

We hypothesize that training over ground will lead to a change in the interlimb coordination
in individuals with asymmetric gait and allow individuals to develop a more persistent
symmetric gait. There are several differences between training on ground and a treadmill,
such as visual flow and vestibular information signaling forward movement that likely limit
the expression of learning in the over-ground context when trained on a treadmill. Visual
cues appear to be particularly important for context awareness. Visual cues, coupled with
prior experience, are so powerful that predictive postural responses cause an individual to
stumble when stepping onto an escalator that is not moving. The body has learned an internal
model that expects an acceleration when stepping onto an escalator, but when that
acceleration does not occur, the person stumbles. A study of split-belt walking showed that
transfer to over-ground walking is enhanced when subjects are blindfolded during training on
the treadmill and tested over ground. Since blindfolding eliminates visual cues about the
environment, this also suggests that vision is a key factor in determining the
context-dependence of learning. Since it is not realistic to blindfold stroke patients during
gait training, we designed the iStride device so that training could occur during over-ground
walking, thus visual cues during training and later walking over ground would be the same.

Data from control subjects using an earlier version of the iStride device (referred to as
GEMS at the time) has been published and a video of this previous version can be found at
http://reedlab.eng.usf.edu/publications/handzic2011GEMS.mp4. In this study, we found that
this earlier version of the device was capable of changing step length as predicted, however
the previous design was too heavy and too tall to be considered practical for testing in
stroke populations. The current version of the iStride device produces similar motion to the
previous version, but it weighs less (under 1 kg) and is shorter (~4.4 cm). We will test the
efficacy of wearing the current iStride device on gait coordination during walking over
ground on individuals with stroke in the clinic and within their own home. All walking will
be performed while subjects are closely guarded by an experienced physical therapist to
prevent falling. The effects of the iStride device on gait coordination will be compared to
those induced on a split-belt treadmill.

The proposed project represents one of the first attempts to build a device that corrects
walking symmetry while walking over ground. Not only would this allow people to experience
gait corrections while performing normal movements, but the simplicity and relative low cost
of these devices would also open up potential opportunities to train at home (for
high-functioning individuals with supervision) and in clinics where a split-belt treadmill is
not available. The studies outlined here will establish whether the iStride device is capable
of changing interlimb coordination of gait, and whether individuals with stroke can use these
devices for rehabilitation purposes. This work will thus build the foundation for future
training studies examining the effectiveness of long-term use of the iStride device for
improving symmetric walking patterns.

The question that this study targets is the modification of human walking patterns for use in
stroke rehabilitation. It is our ultimate objective to show that the iStride device can
change a person's temporal and spatial gait asymmetry into a symmetric gait. We have
demonstrated this in a clinic setting, and now we will test the device within the
participants own home. Our points of reference are results obtained by previous studies with
split-belt treadmills. We are also interested in how altering the interface between a foot
and the ground influences the adaptation to new walking patterns.

Inclusion Criteria:

- age 21-80

- one or more cerebral strokes, but all strokes on same side

- a stroke at least 6 months prior to enrollment

- Gait asymmetry, but able to walk independently with or without a cane

- Not currently receiving physical therapy

- no evidence of severe cognitive impairment that would interfere with understanding the
instructions

- no evidence of one-sided neglect, affecting ambulation

- At least 25 feet of walking space in home (does not need to be a straight line)

- Weight does not exceed 250 lbs

Exclusion Criteria:

- uncontrolled seizures

- metal implants (stents, clips, pacemaker)

- pregnancy

- History of a neurological disorder other than stroke ( Parkinson's, MS)

- Chronic Obstructive Pulmonary Disease

- Uncontrolled blood pressure

- Head injury in the past 90 days

- A myocardial infarction within the last 180 days

- Cannot rely on a rolling walker for ambulation