Introduction
Dropped foot
following stroke can be successfully alleviated using surface stimulation
devices such as the Odstock Dropped Foot Stimulator
(ODFS). These devices stimulate the
common peroneal nerve as it passes over the head of the fibula bone, causing
the foot to dorsiflex. When timed to the gait cycle
using a pressure sensitive switch placed under the heel, the device
significantly aids the swing through phase of gait, reducing the effort of
walking and increasing walking speed.
Despite a good orthotic response and high compliance with these devices,
users report difficulty with using them, in particular, correctly replacing
electrodes. This problem could be
alleviated by the use of implanted electrodes, avoiding the day to day
variation in the user placement of electrodes.
Additionally the sensation from the stimulation would be reduced and the
risk of skin allergy eliminated. The
Methods
The ODFS Questionnaire
A questionnaire
was sent out to 140 experienced (1 year +) users of the ODFS. They were asked to identify what problems
they had experienced and rate the seriousness of those problems on a visual
analogue scale. They were also asked if
they would consider an implanted device.
Clinical trial:
Selection criteria
a) First stroke
of at least 12 months duration with a stable neurology.
b) Dropped foot
identified by an inability to achieve a normal heel strike during walking.
c) Able to walk
at least 100m with aids.
d) Must be able
to understand the use of the equipment and purpose of the trial.
e) Able to give informed consent
f) Aged between
18 and 65
Clinical trial:
Exclusion criteria
a) Evidence of
inversion contractures;
b) Serious
medical conditions
c) Regular surface
peroneal stimulator users
Clinical trial:
Procedure
Subjects were
first assessed through a 1 month base line period to demonstrate
stability. After receiving the implant,
three weeks were allowed for healing of the operation site. 2 months were then
allowed for training with the device and assessments were then repeated in the
following three months, once a new gait pattern had become established.
Clinical trial:
Assessments
Safety was
assessed by nerve conduction studies.
Spontaneous discharges at EMG needle insertion were also examined for
evidence of denervation.
Walking speed
and physiological cost index (PCI) was measured over 10m. PCI is equal to the difference between
resting heart rate and the heart rate at the end of 10m divided by the walking
speed in m/min. This gives an indication
of the effort expended in walking. Three runs were recorded both with and
without the stimulator and the order randomised to compensate for fatigue2. Additionally the distance walked in 6 min was
recorded by walking repeated lengths of a 13.5m corridor.
The implant's
effect on kinematic parameters was recorded using a Biotech Datalink
system. Penny and Giles goniometers were
placed over the ankle, knee and hip joints to measure dorsiflexion, eversion, knee
flexion and hip flexion/extension and adduction/abduction.
User opinion of
the device was collected using a purpose written questionnaire3.
Results
ODFS user
survey: 98 questionnaires were returned from 140 sent to current ODFS
users. On average they had used the ODFS
for 3 years (SD 2.1years). While 52%
were well satisfied or 41% moderately satisfied with the ODFS, problems were
reported with skin reaction (28% - serious 6%), electrode placement (72% -
serious 17%), donning and doffing (58% - serious 15%), coping with wires (58% -
serious 19%) and sensation (36% - serious 3%).
67% would consider an implant.
Clinical Trial
Five people
received the implant. 4 were right sided
hemiplegics and 1 was left sided following stroke.
No change in
nerve conduction velocity was reported following the implant procedure. Nor was there any evidence of denervation
observed on EMG needle insertion.
Mean walking
speed with the device was 24% faster with the implant compared to pre op
without and 14% faster than without the device post op. No significant changes were seen in PCI. Mean distance walked in 6 minutes increased
by 37% pre to post op. (Table 1)
Dorsiflexion and
Eversion were compared for walking with and without the device at the point
just before heel strike. This is before
any loading response has occurred. Use
of the implant resulted in a 15 and 9 degree increase in dorsiflexion and
eversion. There was also a reduction in
hip abduction of 2 degrees that may be due to reduced circumduction in the
swing phase, which is a compensatory response to aid ground clearance. A trend to reduced knee flexion when the
implant was used was also seen. This
could also be less compensatory activity but may indicate knee flexion is
reduced by stimulation (Table 2).
Table
1. Walking speed, PCI and Endurance, pre op and
post op both with and without the implant (n=5). The results here are the mean of 4
measurements made in the final 3 months period.
|
|
Walking speed
m/s No stim |
PCI Bt/m No stim |
Walking speed m/s With stim |
PCI Bt/m With stim |
Endurance Metres |
|
Pre op mean |
0.59 |
0.87 |
|
|
188.92 |
|
Post op mean |
0.65 |
0.75 |
0.74 |
0.71 |
264.81 (with stim) |
|
Mean % change pre / post op |
9.0% p=0.250 |
6.3% p=0.343 |
24.0% p=0.040 |
-2.4% p=0.343 |
37.5% p=0.022 |
|
Mean % change stim / no stim |
|
|
14.2% p=0.022 |
-6.8% p=0.112 |
|
Table
2. Hip, knee and ankle angle while walking with
and without the implant (n=4), at end month 5.
|
|
knee flexion (max swing) |
Hip Flexion (max swing) |
Hip abduction (max swing) |
Dorsiflexion (pre loading response) |
Eversion (pre loading response) |
|
Mean Degrees No stim |
39 |
18 |
7 |
-9 |
-9 |
|
Mean Degrees With stim |
32 |
19 |
5 |
6 |
1 |
|
Difference Degrees |
-7.0 |
-0.7 |
1.9 |
15.2 |
9.2 |
|
Wilcoxon p |
0.07 |
0.36 |
0.03 |
0.03 |
0.03 |
User
questionnaire
Three users used
the device every day while one used it 4 to 6 days a week and one 2 to 3 days a
week. On days that the device was used,
one user used it all day, one 9 to 12 hours, two 6 to 9 hours and one less than
3 hours a day. The device was used for every type of activity by 3 users, while
one used it outdoors only and one for longer walks only. Two users regularly walked between 10 and 100
yards, one between 100 and 500 yards, one between 500 yards and 1 mile and one
walks more than one mile.
From a list of
12 possible replies, the users were asked to select any reasons that were
relevant to them and indicate the most important reason for using the
device. All users said they were more
independent when using the device and 4 said they were more confident and could
walk on uneven ground. 3 users stated
they could walk further, walk faster and walk with less effort when using the
implant and 2 users used it because they could discard a splint or walking
stick. 2 users felt using the device
helped to keep them fit while only one user used it because it prevented them
from tripping or falling. Each user
chose a different main reason for using the device. The reasons were: I can walk faster, I can
walk with less effort, I am less likely to trip or fall, I am more independent
and The exercise keeps me fit.
Two users
required help putting on the device while 3 were independent and the perceived
average time to do this was 4.8 minutes (median 4 minutes). Three users believed their spasticity had
reduced since using the device, one believed it was the same and one believed
it had increased although in the last case this was at odds with the opinion of
the physiotherapist. The device had an
effect on the use of aids. Two people
stopped using walking sticks while walking and one reduced their use of a walking
stick. One user reduced their use of a
wheelchair, one reduced their use of an AFO and one stopped using an AFO.
Three users
stated that the device worked correctly all of the time while 2 stated it
worked correctly most of the time while walking. While sitting, 4 users said
the device never gave false outputs while 1 reported this happened rarely. 2 users stated they always adjusted the
controls themselves while 2 always had an assistant do this for them. Three users stated that adjustments were only
occasionally needed, one only when it was put on and one user never adjusted
the device. Two felt these adjustments
were very easy to make, 1 easy and 2 fairly easy. Three users stated they only adjusted the
position of the box when it was put on while the other users adjusted it
occasionally or every few hours.
The users were
asked if they agreed with the following statements:
|
I am glad that
I have the IMPULSE |
All 5 strongly
agree |
|
I would
recommend IMPULSE to another person |
4 strongly
agree 1 disagree |
|
IMPULSE allows
me more independence |
3 strongly
agree, 1 agrees and 1 indifferent |
|
I feel more
confident when I use IMPULSE |
3 strongly
agree, 1 agree, 1 indifferent |
|
I am more
independent since I received the implant |
2 strongly
agree, 2 agree, 1 no response |
|
IMPULSE has
improved my quality of life |
3 strongly
agree, 1 agree, 1 strongly disagree |
|
IMPULSE has a
good cosmetic appearance when worn |
2 agree, 2
indifferent, 1 strongly disagree |
|
The sensation
from the electrodes is comfortable |
1 strongly agree,
4 agree |
3 users stated
that the box never got knocked in daily use while one said it occurred
occasionally and one said it occurred frequently. The latter user said the control knobs on the
box pressed into the thigh when the knee was at 90 degrees, and the box also
got knocked getting in and out of a car.
Users were asked
to rate the sensation from using the device on a 1 to 10 analogue scale where 1
was no sensation 5, was a mild, comfortable sensation and 10 was a severe
sensation. Two rated the sensation as 1;
two rated it as 5 and one as 6.
Discussion and
Conclusions
The Finetech implanted dropped foot stimulator was found to
perform in a similar manner to surface devices but with the most of the
advantages predicted. However, users
still experienced some problems with its use.
The response from the device is sensitive to small changes in the
position of the transmitter, requiring some care in its placement. Also, three of the users were aware of the
sensation from the device although this may have been from the strong muscle
action required to overcome calf tone.
The trend to reduced knee flexion is a possible concern. However, recently, a new version of the
device that allows the addition of a rising ramp to the output,
has been tried with one subject who reported that knee flexion was made
easier. This may be due to reduced
spastic tone, which may, in the previous version, have been by induced by the
rapid movement causing stretch reflexes.
Overall the
users were enthusiastic about the device.
A larger trial is now required to fully demonstrate its efficacy.
References
[1] Kenney L, Bultstra G, et al. An implantable
two channel drop foot stimulator: initial clinical results. Artif.Organs
2002;26(3):267-70.
[2] Taylor PN, Burridge JH, et al. Clinical
Use of the Odstock Dropped Foot Stimulator. Its Effect on the Speed and Effort of Walking. Arch Phys Med Rehab. 1999; 80 1577-1583
[3] Taylor PN, Burridge JH, et
al. Patient's Perceptions of the Odstock Dropped Foot Stimulator (ODFS). Clin. Rehab. 1999; 13: 333-340
Acknowledgements
We wish to
acknowledge the assistance of Laurence Kenny and Rik Buschman of RDD, Gerrit Bultstra of the University of Twente,
David Francis and David Keeling of Finetech Medical,
Diana Hodgins of ETB and Jonathan Cole of Salisbury
District Hospital. This work was funded
by Medlink.
The device is
available from Finetech Medical ++44 1707 330 942