A novel method to identify migration of small implantable devices

A histologic method has been developed to assess the migration of chronically-implanted intramuscular devices. Bullet-shaped glass devices with varying tip configurations and glass-encapsulated microstimulators of a similar size were loaded with the fluorescent tracer Procion Yellow dissolved in molten glucose. Dissolution of the hardened glucose soon after contact with body fluids released the Procion Yellow, which binds irreversibly to local tissues, thereby marking the initial site of implantation with a localized fluorescent spot. After survival times of 2-7 weeks, histologic analysis usually showed a close physical relationship between the fluorescent spot and the connective-tissue capsule from which the device was extracted. In one case, migration of a sharply pointed device from the deep surface of an implanted muscle was recognized by differences in the location of the dye spot and the site of explantation from nearby fascia. Results suggested that this method could measure migratory distances as small as 5-10 mm.