2001 Conference Proceedings
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Electrical Stimulation Via BIONs: Present and Future
Applications
Anne-Caroline Dupont
Frances J.R. Richmond
Gerald E. Loeb
A.E. Mann Institute for Biomedical Engineering
University of Southern California, 90089-1112
Abstract
We present a new system for the delivery of electrical
stimulation therapy. The system comprises miniature implants and
external transmitting devices. Clinical trials for the treatment
of shoulder subluxation and weak muscles caused by knee
osteoarthritis have started in Canada and Italy. More trials are
underway.
Introduction
Electrical stimulation of weak or paralyzed muscles has been used
for many years in research settings and in clinics. Although
there are many potential applications for this mode of therapy,
clinical implementations have been slowed by technological
limitations of present transcutaneous, percutaneous and
implantable systems. We have developed a new system in which
wireless microstimulators injected into muscles are controlled
and powered by a small external radio transmitter. This system
combines the precise muscle recruitment and easy implantability
of percutaneous electrodes with the long-term safety and
convenience of fully implanted systems. Clinical trials in Canada
and Italy are underway for two of the many potential applications
of this generic technology.
New Technology for Neuromuscular Stimulation
BIONs (BIOnic Neurons) are single channel electrical stimulators
that can be injected into various muscles in a simple clinic
procedure (Figure 1). Each leadless implant receives power and
command signals by radio transmission from outside the body. The
system was developed in collaboration with Queen’s
University (Kingston, Canada), the A.E. Mann Foundation
(Valencia, CA), and the Illinois Institute of Technology
(Chicago, IL) and is licensed to Advanced Bionics Corp. (Sylmar,
CA). A BION is composed of a glass capsule containing an antenna
coil and a miniature circuit board and integrated circuit chip,
and fitted with the two stimulating electrodes sealed
hermetically into each end. The external components (Figure 2)
include the transmission coil to be worn over the body part to be
stimulated and a Personal TrainerTM that stores up to 3 different
stimulation programs. The emitting coil can be configured in a
number of ways such that it can be worn inconspicuously in a
garment, a seat cushion or a mattress, depending on the
application. This coil can power and control up to 256
individually addressable BIONs. Stimulation is simple to
administer; the patient can self-treat at home, reducing the
inconvenience and cost of clinic visits. If the electrical
stimulation is no longer needed, the BIONs can be left in place
because they are then electrically passive, mechanically stable
and biocompatible. BIONs can be imaged safely and effectively
using x-rays, CAT-scans, MRI and ultrasonography (Dupont et al,
submitted).
Figure 1: BIONs and insertion tools Figure 2: transmission coil
and Personal Trainer
Animal testing
BIONs have been used in animals to ensure their safety and
efficacy. Both passive and chronically stimulated implants
generate only a minimal foreign body reaction similar to
biocompatible control materials (Cameron et al., 1998a). These
implants have been shown to be located permanently and stably in
the target muscles (Fitzpatrick et al., 1996) so that thresholds
and muscle responses are stable over time (Cameron et al.,
1998a). Placement of the device near the motor point of the
muscle (usually deep and near the proximal end of the muscle) is
more effective at recruiting the entire muscle during stimulation
(Cameron et al., 1998b). Chronic stimulation in a rat model of
disuse atrophy suggested that low frequency stimulation may be
more effective than tetanic contractions at reversing muscle
atrophy caused by paralysis (Dupont et al., 2000).
Clinical Applications
At present time, five patients have participated in a randomized,
cross-over study of shoulder subluxation after stroke. Three of
these patients received BION implants shortly after their stroke;
two were initially treated as controls with only conventional
physical therapy. Shoulder subluxation is caused by the lack of
support of the humeral head inside the glenoid capsule, due to
flaccid paralysis of the muscles surrounding the shoulder.
Shoulder subluxation is very commonly seen in hemiparetic
patient, resulting in chronic pain and interfering with the
rehabilitation of arm function. Various studies (Faghri et al.,
1994; Baker & Parker, 1986) have demonstrated that electrical
stimulation of the deltoid and supraspinatus muscles can prevent
and reverse this subluxation. In our clinical trials, we implant
one BION in the middle deltoid and one in the supraspinatus.
Patients receive 6 weeks of electrical stimulation applied 3
times a day, starting at 10 minutes per session and extending to
30 minutes per session, with increasing recruitment of the two
muscles. After the 6 weeks of treatment, subjects go off
stimulation for 6 weeks in order to observe the carry-over
effects of the stimulation. After the 12-week study period, they
can chose to keep the system to continue treatments as desired.
Outcome measures include muscle thickness measured by ultrasound,
subluxation measured by X-ray, and manual assessment of range of
motion, muscle strength, and arm function tests. Control subjects
undergo the same assessments but are not eligible for BION
implants until undergoing six weeks of conventional therapy and
follow-up evaluations.
Stimulation thresholds have been stable for all patients and
there have been no adverse reactions. Muscle thickness of the
stimulated deltoid and supraspinatus was seen to increase over
the 6 weeks of treatment, by 6 to 40% depending on the site of
measurement and the muscle and subject measured. In our first
patient, subluxation decreased during treatment from 14 to 1 mm
(arm supported), with a partial relapse during 6 weeks off
therapy (7 mm). A subsequent elective return to therapy reversed
this subluxation. This subject is now on minimal therapy (15
minutes once or twice a day) to maintain his shoulder alignment.
This subject never experienced any pain related to his subluxed
shoulder. Subject number 2 had considerable shoulder pain after
his stroke. The electrical stimulation provided by the BIONs
decreased his subluxation from 17 to 6 mm, but his pain was not
alleviated until he received a cortisone treatment. This subject
also showed a slight increase in the degree of subluxation of his
shoulder during his 6 weeks off therapy. He chose to discontinue
the therapy after the trial. Subject number 3 was a control
subject, with minimal subluxation. He did not experience any pain
of the shoulder and his subluxation decreased from 9 to 6 mm
during the 6 week control period; he chose not to have BION
implants because of his minimal symptoms (Richmond et al., 2000).
As of September 2000 two more subjects, one experimental and one
control, had just started the trials.
Figure 3: X-ray of patient shoulder with BIONs Figure 4: patient
subluxation levels over 6 weeks of treatment A clinical trial
began in June 2000 in Milan, Italy, for the rehabilitation of
hypotrophic leg muscles associated with osteoarthritis of the
knee. Chronic pain leads to disuse and weakness of the
quadriceps, exacerbating damage to the knee joint. Aggressive
exercise therapy to strengthen the quadriceps muscles can
decrease pain as well as increase function (Fisher et al., 1993a;
1993b) but compliance is difficult to obtain. BION implants can
be used to recruit all or most of the motor units at low enough
frequencies to avoid potentially damaging or painful force
levels. Outcome measures such as quadriceps strength, muscle
thickness, pain, and gait analysis will be monitored over 24
weeks.
Preparations for several other clinical applications are
underway. They include incorporation of BIONs into an
FDA-approved footdrop stimulator called the WalkAide (that now
uses transcutaneous stimulation), prevention of venous stasis and
osteoporosis in spinal cord injured patients, and prevention of
spastic muscle contractures in stroke and cerebral palsy
patients. Other clinical trials are also in the planning
stage.
Figure 5: electrical stimulation for the treatment of foot-drop
Conclusion
The BION technology now under study provides a convenient and
cost-effective means of utilizing electrically controlled
exercise in a large range of dysfunctions and muscle groups.
Patients find the therapy easy to self-administer and the
sensations produced to be generally pleasant. BIONs may
eventually provide a basis for functional reanimation of
paralyzed limbs, but this will require incorporation of sensors
for command and feedback signals as well as substantial advances
in control algorithms for multiarticular musculoskeletal
structures. Such development work is underway.
References
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