Neuromuscular electrical stimulation for pressure ulcer prevention

Unrestricted Pressure ulcers (PUs) are debilitating wounds caused by pressure and shear from unrelieved sitting. About 30% of immobilized patients suffer from PUs, and despite a multitude of therapies recurrence rates are as high as 60% annually, even after aggressive surgical repair. This research investigates the use of implantable wireless microstimulators to prevent PUs. BIONs™ ("BIOnic Neurons") are generic neuromuscular stimulators of miniature size and injectable form. They have been demonstrated to activate strong muscle contractions with associated skeletal motion and increases in muscle bulk, strength, metabolic capacity, and vascularity. These effects counteract three major etiological factors of PUs: immobility, soft-tissue atrophy, and ischemia. Historically gluteus maximus has been considered an important actuator in attempting to redistribute seated pressures through neuromuscular electrical stimulation. Using rigid body mass and muscle moment models, the skeletal biomechanics of this system has been analyzed to quantify the relative values of the hip extensors. While gluteus maximus is expected to reduce disuse atrophy and improve circulation, it appears that it is neither required, nor desired, to achieve unloading. Instead hamstring stimulation seems effective at, and capable of, doing so. Using finite element modeling of the soft tissue biomechanics, a simple goal criterion has been determined that seems likely to indicate adequate relief: surface pressures < 8 kPa should be associated with sufficient unloading to reestablish intramuscular blood flow, in all somatotypes.; Based on these analyses, three spinal cord injured patients have each had two BIONs implanted, during reconstructive flap surgery that they already required for PUs. In all cases it has been possible to subsequently stimulate the hamstring and gluteus maximus hip extensors selectively as desired, with promising early results. Once the efficacy of this novel therapy has been proven, its broader application is envisioned as a bilateral, prophylactic treatment, for all immobile patients at risk of PUs. BIONs would eventually be injected percutaneously, controlled and powered via in-chair antennae. To that end a simple BION Insertion Tool has been developed and implemented of non-conductive polymers, to house an implant in its tip for highly accurate placement as an outpatient office procedure.