A percutaneously implantable wireless neurostimulator for treatment of stress urinary incontinence

Stress urinary incontinence is a common problem in which there is involuntary urine leakage during activities that increase abdominal pressure. Although it is not a life-threatening problem, it has high prevalence, affecting millions of elderly people. Most patients with this problem have weakness or damage of the external urethral sphincter and pelvic floor muscle as a result of childbirth or prostate surgery. Invasive surgical treatment such as vaginal tape and hydraulic sphincters have significant long term-complications. Voluntary muscle exercise program have been documented to produce excellent results but most patients find it difficult to perform such exercises correctly or consistently enough to obtain such results. Previous attempts to induce muscle exercise by electrical stimulation failed due either to unpleasant sensation from external electrodes, or to connection failure of long leads to conventional, fully implantable stimulators. Intramuscular electrical stimulation via a minimally invasively implanted microstimulator should overcome these challenges. ❧ We have developed a single channel, monolithic microstimulator (3.5mm diameter * 10 mm long) that can be implanted close to targeted motor axons via minimally invasive procedure to generate charge-regulated pulses for strong muscle contraction. The implanted device receives stimulus power and timing by inductive coupling from a radio frequency transmitter in a seat cushion. The physician and patient can use an app in a tablet computer or smartphone to prescribe exercise patterns and control and record daily use via Bluetooth communication to the seat cushion. ❧ Preclinical testing demonstrated that the implant produces the desired output pulse (0.05-2.8µC) up to 12cm from the face of the seat cushion. Accelerated life testing in vitro of the non-hermetic epoxy encapsulation demonstrated expected lifetime in vivo > 1 year. Chronically stimulated implants in an animal study reliably activated skeletal muscle without apparent discomfort and were well anchored by minimally reactive connective tissue encapsulation after 1-3 months. The validated system is now being used in a clinical trial to demonstrate safety and efficacy. The primary outcome measure is a conventional pad weight test for urine leakage during controlled exercise. The inert, passive implants are intended to be left implanted after 3 months of daily, electrically induced exercise.