The long-term effects of an implanted drop foot stimulator (ActiGait®) on walking capacity in patients with stroke

In the Netherlands, every year approximately 40.000 persons sustain a
cerebrovascular accident (CVA or stroke). An estimated 20% of all stroke
survivors suffer from a *drop foot*, which is caused by the inability to
(selectively) activate the muscles that dorsiflex the ankle joint. While
walking, patients with a drop foot tend to drag the foot during the swing phase
(lack of toe clearance), which places them at risk for tripping. Furthermore, a
drop foot is usually part of a more generalized stereotyped movement pattern of
the affected leg, characterized by insufficient knee and hip flexion during the
swing phase. This lack of swing leg flexion predominantly causes stroke
patients to experience difficulties when stepping over obstacles, due to
insufficient foot clearance. In stroke patients with a drop foot, the common
treatment is the prescription of an ankle-foot orthosis (AFO). Devices using
functional electrical stimulation (FES) have been introduced as an alternative
treatment method for drop foot. These devices artificially activate the muscles
that dorsiflex and evert the ankle joint during the swing phase of gait.
Actigait®, an internal FES system, directly stimulates the common peroneal
nerve through 4 distinct electrodes embedded in a cuff, that is surgically
placed around the nerve. The stimulation device selectively controls the 4
electrodes within the cuff, in order to differentiate between fibers
predominantly branching to the superficial peroneal nerve (activating the
peroneal muscles) and those to the deep peroneal nerve (activating the anterior
tibial muscle).
The first hypothesis of the proposed study is that the Actigait® system will
not only effectively and selectively elevate and control the ankle joint during
the swing and early stance phase, but that it will reduce the stereotyped
movement pattern of the affected leg (see above) as well. This may result in an
improvement of the quick, online adaptability of the step. On irregular
terrain, the locomotor pattern has to be continuously adjusted in order not to
stumble or fall. Therefore, these complex gait skills are essential for
independent and safe mobility in daily life and highly associated with fall
incidence. Especially in this domain of complex gait skills, Actigait® is
expected to be superior to a conventional AFO or orthopedic shoes. Preliminary
results from our previous study confirm this hypothesis and the proposed study
is necessary to further explore the potential effectivity of ActiGait® in a
broader patient population.
A second aspect of the proposed study is the possible training effects of FES.
Over time, volitional control of movement may improve with FES as a consequence
of motor re-learning. However, until now, the evidence for training effects of
peroneal FES is not yet convincing. In addition, in studies that found such
training effects, the adaptation mechanisms underlying these effects remained
poorly understood. Neuroplastic changes of peripheral as well as central
structures may contribute to the observed benefits. For example, muscle fibers
may be strengthened and the recruitment of spinal motorneurons may improve, but
also strengthening of corticospinal connections may explain the effects of FES
in the long term.

The main goal of this study is to evaluate the functional efficacy of the
Actigait® system as a FES device, as well as its training effects with regard
to (complex) walking. In addition, with regard to the training effects of FES,
we intend to discriminate potential changes in the integrity of the
corticospinal tract from more peripheral changes.

Patients will be informed about this study by their physiatrists and eligible
patients will be invited to participate. An intake visit will be planned with
the physiatrists of the department of rehabilitation in RUN-MC. If the response
to external FES is not yet known, the patient*s response will be evaluated
during a 4-week test period with external FES prior to inclusion. After 4
weeks, the Actigait system will be implanted in a 45-minutes neurosurgical
procedure. Three weeks after surgery, the system will be set up and the patient
can start its use.

The quality of both unobstructed and obstructed gait skills will be assessed.
Furthermore, changes in corticospinal excitability as a result of FES will be
determined by measuring MEPs in the leg muscles resulting from transcranial
magnetic stimuli. Effects on both the gait ability and the corticospinal
integrity will be evaluated at baseline (before implantation), at *short-
term* (after a 2 weeks adaptation period), *middle-term* (8 weeks ) and *long-
term* (after 26 and 52 weeks of use). For each of these 5 evaluations, two
visits will be scheduled at the mobility lab in the Radboud University Nijmegen
- Medical Center (RUN-MC). In week 1, 2, 3, 5, 8 en 26 after the start with
Actigait®, a telephone interview will be held to evaluate the extent of usage
and the activities performed with Actigait. Finally, patients* satisfaction,
social participation and physical ability will be assessed by means of
questionnaires, and the activitation level by means of a pedometer. This will
be assessed regarding their normal walking condition (which may include an AFO
and/or shoe adaptation) and regarding Actigait®

Implantation and usage of a FES system to correct drop foot

The common risks associated to (minor) surgical procedures to the extremities,
like wound infections, apply to this study. The use of a cuff-electrode around
the n. peroneus communis could lead to nerve damage. In a prior study in
RUN-MC, this complication occured due to a change in the the surgical
procedure. The procedures have been adjusted and no further complications
occured with the renewed procedures. Also in a prior study on the safety of the
Actigait system by Burridge et al. (2007), in which the same surgical procedure
was used as will be in the proposed study, no such events occurred.