The presently available BION1 implants provide accurate and reproducible muscle stimulation, but they do not provide detection of volitional command signals or sensory feedback to permit fine control (see below). They also require a transmitting coil to be in close proximity to the implants during stimulation. The present version of the RF power and control system consumes approximately 2 W of power and is designed to be powered by an AC/DC converter plugged into a conventional receptacle rather than a portable battery. Thus the BION1 system is most suitable for TES applications in which a sedentary patient uses the system to exercise and strengthen muscles for relatively brief periods each day.
For the initial clinical testing of the new BION technology, we selected an application in which it is relatively easy to implant the devices, assess their functionality, and achieve a clear and quantitatively measurable clinical outcome in a reasonably short period of time. This is the prevention of shoulder subluxation in stroke patients by TES-induced muscle exercise. The most common residual defect of a stroke is paralysis of the contralateral arm, with atrophy of the affected muscles. The majority of these patients go on to develop chronic pain in the affected shoulder as the weight of the arm gradually stretches the flaccid muscles and pulls the humeral head out of its socket (the glenoid fossa).23 Conventional treatments with slings and painkillers is generally ineffective and tends to interfere with any rehabilitation effort. Electrical stimulation of the affected muscles via skin surface electrodes (so-called deep transcutaneous electrical neuromuscular stimulation) has been reported to prevent and reverse this problem,24 but each treatment session requires a trip to the clinic to apply the electrodes and adjust the stimulation parameters.
Figure 3.6 shows the clinical system for use of BION implants to prevent shoulder subluxation. One or two BIONs are implanted into each of the two key muscles: the middle head of the deltoid and the supraspinatus. The location can be determined accurately before each BION is implanted by delivering stimulation pulses from a conventional stimulator through the modified trochar of the insertion tool. The insertion tool is based on a conventional 12 gauge Angiocath™ needle, consisting of a plastic sheath about 10 cm long over a sharp, removable trochar for penetrating skin and fascia. By adjusting the stimulation intensity as the target muscle is palpated, it is possible to identify that the tip of the insertion tool is within the target muscle and close enough to its innervation zone to permit reasonably strong recruitment. The trochar is then removed while holding the sheath in place and the BION is slipped down the sheath and extruded from the tip by pushing a blunt plunger while withdrawing the sheath.
After allowing the BIONs to settle in situ for a few days, the clinician determines the threshold for muscle activation at each site and develops an exercise program based on a sequence of ramped and overlapping trains of stimulation at the various sites. A software package has been written in Visual Basic 5 to provide an intuitive graphical user interface for the clinician. It automatically tracks all of the clinically relevant data in a time-stamped relational database, including the serial numbers, addresses, and locations of each implant; the electrical thresholds over time; the various exercise programs devised for the patient's use; and the compliance of the patient in using the system at home. The exercise programs are downloaded from the clinician's personal computer into a microcontroller-based portable device (called a Personal Trainer™) that the patient operates simply by hitting start and stop buttons. The elapsed usage is uploaded into the database when the patient returns to the clinic with the Personal Trainer for testing and reprogramming as needed.
Several outcome measures have been validated in preclinical testing or adopted from the clinical literature on shoulder subluxation. The most direct demonstration of efficacy is the prevention of the loss of muscle mass that normally accompanies disuse atrophy. Imaging techniques such as magnetic resonance (MR) and x-ray computed tomography (CT) have been used to measure the cross-sectional area of individual muscles,25 but they are lengthy and expensive procedures to perform repeatedly. Measurement of diameter from well-positioned ultrasound scans has
Treating shoulder subluxation in stroke patients:
Treating shoulder subluxation in stroke patients:
been validated by comparison with MR in the same normal subjects.29 Such scans will be used to measure atrophy by comparison with the unaffected arm. Other important outcome measures include distance of subluxation as measured by palpation and oblique radiographs, and range of passive motion without pain, which declines rapidly as subluxation develops.
At the time of this writing, two stroke patients have been implanted with two BIONs and are receiving regular TES to build up atrophic deltoid and supraspinatus muscles. The study will eventually include 30 subjects in a randomized, prospective, controlled, cross-over paradigm.
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