Abstract
Some of foot drop patients can generate voluntary
electromyogram, which is not sufficient to dorsiflex an
ankle joint. We developed a gait assist device that employs an electrical
stimulation for these patients. When surface EMG of tibialis anterior muscle is
observed, an electrical stimulation is applied to the same electrodes. The
stimulation is repeated 15 times per second with bipolar pulses with the
duration of 0.1 to 0.5 ms. The pulse duration is
changed according to the amplitude of the voluntary EMG. The duration is
calculated with a microcomputer. The device is worked with a 006P-type dry
battery (9 V), and is mounted on a knee supporter for sport players. The
electrodes are also mounted on the inner side of the supporter for easy don and
doff. Patients improved the foot drop and inversion of their ankle joints.
Introduction
Drop
foot is one of the sequelae of stroke. For those patients an ankle-foot orthoses
(AFO) is widely used.
Some
of these patients can generate voluntary electromyogram, but it is not
sufficient to dorsiflex the ankle joint. If we can detect the EMG and give
electrical stimulation to the same muscle, the patients can walk without the
AFO.
We
developed a gait assist device that employs an electrical stimulation for these
patients.
The studies on electrical stimulation that
restore standing and walking after spinal cord injury or stroke are being done
by the group of University of Alberta (Canada), the group of University of
Ljubljana (Slovenia), and the other. [1]-[3]
Several types of devices that assist walking have been developed by now. One
type of the devices is equipped with a force sensor mounted under the heel of
the healthy leg for triggering the stimulation, e.g. SAMMS (BEAC Biomedical,
We intended to develop a more miniaturized
and simpler device for daily use.
Design and Development of the Device
Our device stimulates common peroneal
nerve that governs dorsiflex muscle group, i.e. tibialis anterior m. (TA),
extensor digitorum longus m., fibularis longus m. (FL), fibularis brevis m.
(FB). The latter three muscles also work to everse a foot. The block diagram of
the device is shown in Fig.1. One of the electrodes is
mounted on TA belly and the other is on its origin where the common peroneal
nurve runs. When the electrodes detect voluntary EMG, it is amplified and transferred
to a microcomputer (PIC16C711; Microchip, USA),
which A/D converts the EMG and calculates the stimulation pulse duration,
according to the EMG amplitude.(Shown in Fig. 2)
The pulse repetition is pre-determined as 15 Hz. The microcomputer generates a
proper pulse train and it is transferred to a stimulation circuit. The
stimulation circuit is connected to the same electrodes that detect voluntary
EMG. Since the stimulation voltage is thousands times larger than voluntary
EMG, the microcomputer switches
off the EMG from the stimulation circuit in order not to be interfered from the
stimulation artifact.
The
device is worked with a 006P-type dry battery (9 V), and mounted on a knee supporter for sport players. The
electrodes are also mounted on the inner side of the supporter, for the easy
don and doff.
It is one of the features of our device
that it conducts both of output of stimulation and detection of the EMG by one
set of electrodes. It made easy to attach the device and electrodes.
Fig. 1 The block diagram of the device
Fig.2 Control of the
stimulation pulse duration according to
the EMG amplitude
Results and
Discussion
The
device was used for two stroke patients (57 y/o male, and 55 y/o female), after informed consent. They have drop-foot and spasticity of gastrocnemius
m. and hamstrings m. They daily walk with an ankle-foot orthoses and a T-cane.
They
could walk with our device and a T-cane. Stimulator was on, at the
start of swing phase and stance phase, when dorsiflex
muscle group
contracted and the EMG of these muscles were detected. (Shown in Fig. 3) Their inversions were found to be improved by a video
picture analysis. (Shown in Fig. 4) Thus, the splasticity seemed to be decreased.
It should be proved by the decrease of the EMG of gastrocnemius m. and
hamstrings m.
Since they could smoothly swing affected
leg, by using our device, their gait speed became faster than the speed without
stimulation.
Since
after stop using the device they returned to the previous gait posture, the
device seems not to give plastic effects to the spasticity.
The
device was so compact that a patient could easily put on and take off.
Fig. 3 The period of activity
of tibialis anterior m. in gait [5]
(a) (b)
Fig. 4 Appearance of gait with
stimulation (a), and without stimulation (b). Inversion is disappeared in (a).
References
[1] Stein RB: Functional
electrical stimulation after spinal cord injury. J Neurotrauma 1999; 16(8):713-7
[2] Dai R,
Stein RB, Andrews BJ, James KB, Wieler M: Application of tilt sensors in functional electrical
stimulation. IEEE Trans Rehabil Eng 1996; 4(2): 63-72
[3] Matjacic Z, Munih M, Bajd T,
Kralj A, Benko H, Obreza P: Wireless control of functional electrical
stimulation systems. Artif Organs 1997; 21(3): 197-200
[4] Nikolic ZM, Popovic DB, Stein
RB, Kenwell Z: Instrumentation for ENG and EMG recordings in FES systems. IEEE
Trans Biomed Eng 1994; 41(7): 703-6
[5] Nakamura R, Saito H:
Fundamental Kinesiology 5th Edition, Ishiyaku Publishers, Inc., 2000, Japan
Acknowledgments: We wish to express our gratitude to the staff
members of the physical therapists of Keio University Tsukigase Rehabilitation
Center for their warm support.