Restoring Gait in Stroke Patients Using Functional Neuromuscular Stimulation

Gait deficits following stroke often are disabling and can dramatically reduce a patient's mobility. Affected patients are at high risk for debilitating falls that may result in fractures. Subsequent burdens include costly health care and reduced independence and quality of life. Unfortunately, conventional rehabilitation therapies, such as over-ground walking (OG), and body weight-supported treadmill training (BWSTT), are not always successful in restoring gait in this patient population.

Following stroke, limited success can be achieved in improving muscle strength,^1,2 passive and active range of motion,^3,4 muscle tone,⁵ muscle re-education,^6,7 and gait^8-12 with single-channel implanted and multichannel surface stimulation systems. However, adverse effects as well as limitations of the technology itself make these systems less than ideal. Adverse effects include pain caused by surface electrodes, and technologic drawbacks include poor repeatability in muscle response from one day to the next, challenges patients have in donning the surface-stimulation system, the inadequate number of channels available, and a lack of portability.

Extremely encouraging data on multichannel functional neuromuscular stimulation (FNS) is emerging from several clinical trials, however. The studies, led by Janis Daly, PhD, MS, director of the Stroke Motor Control and Motor Learning Laboratory and associate director of the Cleveland Functional Electrical Stimulation Center of Excellence at the Louis Stokes Cleveland VA Medical Center, show that FNS provides significant improvement in strength, coordination,¹³ and gait component coordination.¹⁴ In addition, findings from the most recent trial suggest that FNS can restore voluntary gait components in chronic stroke patients.¹³

Following the protocol, 32 patients who had had a stroke at least 1 year before study participation were randomized to receive either FNS using intramuscular electrodes (FNS-IM) or no FNS intervention. Eligible patients included those who could not clear the floor normally in the sagittal plane, walk without human assistance, or perform hyperflexion or hyperextension of the knee while standing; those who did not have passive joint range movement of the hip, knee, or ankle equivalent to that normally required for walking or who did not have normal corrected distance vision. Also, patients could not be participating in other rehabilitation programs when they entered the study.

All participants underwent 4 treatment sessions per week for 12 weeks. Each session was 1.5 hours and included 0.5 hours of coordination exercises, 0.5 hours BWSTT, and 0.5 hours of OG. Both the FNS-IM and non-FNS groups engaged in identical exercises and gait component practice that were aimed at restoring voluntary ankle dorsiflexion during swing, knee flexion during swing, knee flexion at toe-off, knee extension before heel strike, and knee and pelvic control during stance.

The results showed that FNS-IM produced a significantly greater gain for knee flexion (P = .049) and gait component execution (P = .003) compared with no FNS. In total, 64% of the FNS-treated patients experienced gains of between 2 and 6 points on the Tinetti gait and balance scales, compared with only 13% in the group that did not receive FNS-IM. No gains were reported in 50% of the non-FNS group, compared with 14% in the FNS-IM group.

"One of the reasons why this paper is important is that it shows that voluntary coordinated gait components can actually be restored," Daly remarked in an interview with Applied Neurology. "I emphasize the word 'voluntary' because FNS is used to drive the body and drive the gait pattern for some patient populations. In contrast, the important fact about this study is that the results were obtained according to voluntary walking. In other words, we didn't use the stimulation when measuring any of the outcomes. We only used the stimulation for the treatment. So there was a recovery of voluntary walking capability-a recovery of the coordinated gait components," she explained.

Secondary outcomes included self-reported functional milestones. The analysis showed that both groups reported subjective improvements within this category, but that improvements were much more robust among patients receiving FNS-IM (53 self-reports for the FNS-IM group versus 11 for the non-FNS group). The domains included mobility at home, mobility within the community, life-roles participation, and pain resolution in the hip and back.

For mobility within the community, 3 patients treated with FNS-IM progressed from a wheelchair to community rehabilitation; none of the patients in the non-FNS group were able to do this. Walking endurance on even terrain increased from 0.3 miles in both groups at baseline to 1.0 mile for 8 patients in the FNS-IM group and 4 patients in the non-FNS group.

In the life-roles participation domain alone, 18 FNS-IM recipients reported improvements ranging from preparing dinner to slow dancing and boating. Notably, patients reported progressing from assisted living to independence. Only 2 patients in the non-FNS group reported improvements in the life-roles participation domain.

A GROWING BODY OF EVIDENCE

Daly has been instrumental in building data on the value of FNS-IM over the past few years. "My first case study-a single case study-provided an unexpected finding: the swing-phase pattern was restored to normal in a patient in the chronic stage following stroke," Daly said. "That was quite a startling finding."

In research findings published in 2001, improved strength was exhibited in 77% of muscles treated (improvement of at least 1 manual muscle test grade per muscle).¹⁵ In another study, improvements in balance and gait were also evident by the Tinetti balance and gait scales: P = .022 and P = .029, respectively.¹⁶ Furthermore, an overall 1413.9 months of electrode use was free of mechanical failure.¹⁷ The result of improved gait patterns was "enhanced quality of life in terms of personal care capability and leisure and social activity levels," Daly said.

In research published in 2004, significant improvements were seen in the volitional peak swing knee flexion and volitional mid-swing ankle dorsiflexion (P < .05) among patients receiving FNS-IM.¹⁴ Values of between 16 and 56 degrees were reported for post-treatment peak swing knee flexion (P < .05). These improvements were maintained for 6 months.

SURFACE FNS VERSUS FNS-IM

Although surface FNS induces muscle contractions and coordinated movements using surface electrodes, FNS-IM involves electrode implantation within the muscle and an externally worn stimulator. The intramuscular electrodes are implanted using conscious sedation. An incision is not made to place them. The surgical team uses a probe to locate the motor point of the paralyzed muscle. The point is marked, and a 17-gauge sheath is passed over the probe; then another, slightly larger (15-gauge) sheath is placed over the smaller sheath. This allows for gentle expansion of the passageway into which the electrode will be placed. Next, the probe and the inner sheath are removed, and the electrode, mounted on a 26-gauge needle, is inserted through the remaining sheath to the predetermined point in the muscle. The needle is then withdrawn, leaving the electrode in place.

The lead wires are subcutaneously routed to a common exit point, and the external lead wires are connected to a small pin connector (about ½ inch square) that mates with another small pin connector, which is connected to the ribbon cable that is attached to the stimulator. "The lead wires are 10-strand, 16-gauge stainless steel, fine wire-8 in total-and the patient doesn't feel them," Daly explained. "Patients can swim and take showers with the lead wires in place," she added.

At the end of the 12-week protocol, the electrodes are removed in a similar fashion to the way they were implanted. "We perform a 30-minute procedure and a local anesthetic. As we exert a constant force on the lead wire, it slides out through the skin," Daly said.

"An electrode fragment often remains in the body," Daly continued. She and colleagues found that this causes no harm to the patient. In their study published in 2001, neither infections nor symptoms were associated with fragment remnants.¹⁷ "This was a 10-year study. Even to date, the zero-infection rate and absence of symptoms remain accurate," Daly said. She added that an update on a larger cohort will be available in the future.

IMPLEMENTATION

Patients involved in the FNS-IM study protocols are evaluated by therapists. The therapist customizes the FNS-IM patterns using special software templates that Daly devised over a decade ago. FNS-IM patterns customize the treatment regimen according to individual patient needs. "The treating therapist customizes the templates according to the strength and coordination assessments," Daly explained. "We also have a team of therapists and engineers that test the electrodes to determine the electrode threshold and a comfortable stimulus range," she said. They then use those values to customize the FNS-IM treatment patterns, which are subsequently downloaded into the simulator.

"The patient turns on the stimulator and his or her name appears," Daly explained. There's a finger switch array with 4 buttons attached to the stimulator: the top 2 are for scrolling up and down, and the bottom 2 are "go" and "stop" switches. The patient uses the scroll button to select the exercise that he wants to practice. "When the exercise appears, he hits the 'go' button, and it activates his muscle," Daly said.

CLINICAL ADVANTAGES

Compared with surface stimulation and other forms of rehabilitation therapy, intramuscular stimulation has many clinical advantages. "One advantage is that once the electrodes are placed, they stay in place for the duration of the 12-week protocol," Daly said. "Therefore, there is a consistent muscle response from day to day," she said. Another advantage is that the FNS-IM system can be applied in a timely manner. "The patient and therapist don't have to replace the electrodes every day as is the case with surface stimulation," she said. "In the lower extremity, we need many muscles to coordinate the gait pattern and to apply 8 pairs of electrodes for a therapy session takes almost the entire session. Then there's no time for treatment," she said. "Our 8-channel FNS-IM system can be donned in a timely manner; it takes less than 5 minutes."

POTENTIAL COST SAVINGS

The implications from these data are broad and include the potential for substantial cost savings for medical facilities as well as stroke patients and their families. Currently, the standard of care for patients with chronic stroke-related neuromuscular deficits involves assessment of new symptoms or diagnoses. Lack of coordination, gait deficits, and dysfunction from the original stroke are typically treated for only up to 3 months, notwithstanding the degree of handicap.¹³ Daly and colleagues¹³ provide approximately 21 more treatments in their FNS-IM protocol than is currently provided with conventional rehabilitation therapy, "assuming a best-case conventional scenario of 3 weeks of daily inpatient visits [15] and 6 weeks of twice-weekly outpatient visits [12 visits, for a total of 27]."

They postulate that the gains reported with respect to gait components and functional parameters in the FNS-IM protocols "may justify 21 visits." The cost of combined FNS-IM and electrode placement is approximately $4960, which may be offset through statistically significantly greater improvements in mobility and quality of life. The incremental cost of the FNS-IM therefore warrants further cost-analyses, said Daly.

In addition, costs associated with patient assistance, such as home care or running of errands, may be reduced by increased patient mobility. "Community mobility for stroke survivors could prove to be a significant cost savings to society," Daly added.

THE FUTURE

Presently, FNS-IM is used in research protocols only, which are funded by grants awarded by the Department of Veterans Affairs Office of Rehabilitation Research and Development. Daly's interdisciplinary team of about 20 people, including engineers, clinicians, neuroscientists, statisticians, and physicists, are working to perfect the technology so that it may be used in an everyday clinical setting. The results are already generating excitement. To learn more about the studies, call the research team clinical coordinator, Jean Rogers, at 216-791-3800, Extension 3830.

REFERENCES

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14. Daly JJ, Roenigk KL Butler KM, et al. Response of sagittal plane gait kinematics to weight-supported treadmill stimulation and functional neuromuscular stimulation following stroke. J Rehabil Res Dev. 2004;41:807-820.

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CLAIRE SOWERBUTT is a medical news writer in Vancouver, British Columbia.