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

Baker LL and Parker K: Neuromuscular Electrical Stimulation of the Muscles Surrounding the Shoulder, Phys Ther, 66(12): 1930-7, 1986. Cameron T, Loeb GE, Peck RA, Schulman JH, Strojnik P, & Troyk PR: Micromodular implants to provide electrical stimulation of paralyzed muscles and limbs,’ IEEE Trans Biomed Eng, 44 (9): 781-90, 1997.

Cameron T, Liinamaa TL, Loeb G, and Richmond FJR: Long-term biocompatibility of a miniature stiumlator implanted in feline hind limb muscles, IEEE Trans Biomed Eng, 45(8): 1024-35, 1998a.

Cameron T, Richmond FJR and Loeb GE: Effects of regional stimulation using a miniature stimulator implanted in feline posterior biceps femoris, IEEE Trans Biomed Eng, 45(8): 1036-43, 1998b.

Dupont AC and Richmond FJR: Effects of Chronic Stimulation Patterns in an Animal Model of Disuse Atrophy, Proceedings of IFESS, June 2000.

Dupont AC, Sauerbrei EE, Fenton PV, Shragge PC, Richmond FJR, and Loeb GE: Real-Time Ultrasound Imaging to Estimate Muscle Thickness: A Comparison with MRI and CT. J Clin Ultrasound (submitted).

Faghri PD, Rodgers MM, Glaser RM, Bors JG, Ho C, and Akuthota P: The effects of functional electrical stimulation on shoulder subluxation, arm function recovery, and shoulder pain in hemiplegic stroke patients, Arch Phys Med Rehabil, 75: 73-8, 1994.

Fisher NM, Gresham GE, Abrams M, Hicks J, Horrigan D, and Pendergast DR: Quantitative effects of physical therapy on muscular and functional performance in subjects with osteoarthritis of the knees, Arch Phys Med Rehabil, 74: 840-7, 1993a.

Fisher NM, Gresham G, and Pendergast DR: Effects of quantitative progressive rehabilitation program applied unilaterally to the osteoarthritic knee, Arch Phys Med Rehabil, 74:1319-26, 1993b.

Fitzpatrick TL, Liinamaa TL, Brown IE, Cameron T, and Richmond FJR: A novel method to identify migration of small implantable devices, J Long-Term Effects Med Implants, 6(3&4)L 157-68, 1996.

Granat MH, Maxwell DJ, Ferguson ACB, Lees KR, and Barbenel JC: Peroneal stimulator: evaluation for the correction of spastic drop foot in hemiplegia. Arch Phys Med Rehabil, 77: 19-24, 1996.

Richmond FJR, Bagg SD, Olney SJ, Dupont AC and Loeb GE: Clinical Trial of BIONs for Therapeutic Electrical Stimulation, Proceedings of IFESS, June 2000.

Taylor PN, Burridge JH, Dunkerley AL, Wood DE, Norton JA, Singleton C, and Swain ID: Clinical use of the Odstock dropped foot stimulator: its effect on the speed and effort of walking. Arch Phys Med Rehabil, 80: 1577-83, 1999.


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