RESNA 26th International Annual Confence
We have been using BIONs™ - wireless, injectable stimulators - in two applications to strengthen muscles weakened by disuse atrophy: preventing and reversing post-stroke shoulder subluxation in hemiplegic subjects (two studies, one sub-acute and one chronic) and strengthening quadriceps muscles in persons with knee osteoarthritis (one study). Subjects self-administered therapy (3 sessions/day, 10 to 30 min/session) for 6 or 12 weeks. Results (from 16 subjects) have shown that BIONs are easy for the physicians to implant and easy for patients to use. Implants are stable over time periods as long as 20 months. Shoulder subluxation was reduced by 55% ± 54%; knee function was enhanced by 65% ± 24% and knee pain decreased by 78% ± 18%.
Various types of neuromuscular electrical stimulators have been developed to rehabilitate paretic and paralyzed muscles in clinical settings, but their common use is inhibited by the limitations of available technologies. Recently, single-channel injectable devices called BIONs have been introduced. They are small (16 mm long x 2 mm diameter), self-contained, hermetically sealed and many can be implanted in one body area. They receive power and digital commands by inductive coupling to an externally generated RF field. Physicians can implant BIONs by injecting them through a 12-gauge hypodermic needle. Each implant can deliver currents up to 30 mA and pulse widths up to 514 ìsec. In vivo and in vitro tests were described previously (1-3).
Hemiplegic patients 3-12 weeks post-stroke with or at risk of shoulder subluxation are randomized into a control or BION therapy group. In the BION therapy group, one BION is implanted in each of the middle deltoid and the supraspinatus muscles. The therapy consists of 6 weeks of self-administered stimulation sessions (3 per day), starting at 10 min. and increasing weekly to reach 30 min. per session. Intensity is also increased weekly until the muscle contracts maximally. This is followed by 6 weeks without BION therapy to study whether the effect has some permanence. In the control group, no BION therapy is offered for the first 6 weeks. After these 6 weeks, the control group is offered BION therapy. During the trial, subjects are assessed regularly for subluxation, arm range of motion (ROM), arm strength, arm function, pain, muscle thickness (ultrasound) and stimulation thresholds.
Post-stroke (>6 months) patients with stable shoulder subluxation follow a protocol similar to that of the subacute shoulder subluxation study. If the subluxation is not reduced after the initial 6 weeks, more intense therapy is then used for 6 weeks in an attempt to reverse the subluxation. Assessments are similar to those used in the study of subacute shoulder subluxation.
Patients with knee osteoarthritis are first assessed during a 12 week baseline period and then receive one BION implanted close to the femoral nerve in the groin. Therapy follows for 12 weeks. Three sessions of stimulation per day have an initial period of 10 min. and are gradually increased to 30 min. Assessments are carried out throughout the study and include the Western Ontario McMaster knee test (WOMAC), the Knee Society Test, pain, and muscle cross-section area (MRI scans).
Fourteen subjects have been implanted with BIONs in these three studies to date. Clinicians found the BIONs were easy to implant in these two areas. The subjects found that the implantation caused little pain either during or after the procedure. The implantation time (including searching for a low threshold site) was approximately 20 minutes per device. Typically, patients found that the therapy was pleasant and had no trouble complying with their treatment. Patients self-administered the therapy at home or in the hospital if they were not discharged at that time, thus avoiding the cost of clinic visits. Of the five control patients in the subacute stroke shoulder study, three chose to receive BION therapy after their 6 weeks of observation. Analysis of tissue around the BIONs in one subject who died of unrelated causes showed minimal foreign-body reaction; the subject had used his implants regularly for almost two years. In all three studies, all thresholds of implanted BIONs remained stable over time.
Data are available from 5 control subjects, 5 stimulated subjects (both control and the original TES), and 3 implanted subjects who either did no comply with treatment because of worsening mential state (1 subject) or problems with the device electronics that have since been resolved (2 subjects) (referred to as `non-compliant'). Subluxation was reduced significantly (at the 0.05 level at least) in the five stimulated subjects, regardless of the method used to measure subluxation (Table 1). No significant changes in subluxation were seen in the control group and the non-compliant subjects. Other outcome measures, such as range of motion, strength, arm function, and muscle thickness showed no significant changes after the 6 weeks of therapy. One subject had pain at the onset of the study and it disappeared; the others had no pain at study onset, and no pain developed.
only one subject has completed the study as of December 2002.
five subjects have completed the study; all have chosen to use BION therapy after the clinical trial had been completed. Improvements in function were seen: WOMAC scores went up 65 ± 24% (P < 0.01) and the Knee Society Function Score went up 8.3 ± 7. % (P < 0.05). Pain decreased: Visual Analogue Scores went down 78 ± 18% (P < 0.002); the Knee Society Pain-Free Index showed improvement of 60 ± 82% (P < 0.05) (Table 2). As of December 2002, the MRI data was still being analyzed. In one subject a BION was removed because of discomfort felt when sitting, perhaps because the folded tissues around the implant pressed against it.
In the subacute shoulder subluxation and the knee osteoarthritis studies, results are encouraging, despite the small number of subjects (5 in each study) having received the therapy according to current protocols. In both studies the principal outcome measures (subluxation and knee function) have already shown significant improvement. The improvement seen in the knee study resulted in the cancelling of scheduled knee surgery for at least one subject. Postponing arthroplasty provides an immediate health care cost savings and reduces the longevity required of the knee prosthesis if and when it is finally required. We were encouraged by the generally high level of compliance of the subjects, who reported the therapy to be pleasant and easily integrated into daily activities. BIONs are relatively inexpensive to manufacture and to implant compared to fully implanted systems with leads. Patients find it easy to deliver regular therapy without professional supervision. Thus, we believe that BIONs will eventually be integrated into clinical practice to treat many types of paralysis and disuse atrophy. We are currently developing some of these other applications for future clinical trials. The ease of use of this therapy makes it a practical treatment for patients who need chronic electrical stimulation to maintain their health and function.
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