Design and Implementation of an Implantable Goniometer

A design for an implantable goniometer is presented with potential application in control of neural prostheses. Joint angle is detected magnetically utilizing a linear Hall-effect device and two permanent magnets. The transducer was evaluated in bench tests to determine its response along three orthogonal axes. A preliminary version of the system was then evaluated on a dog cadaver limb. An improved version was bench tested on a plastic model of the human knee. Finally, a fully implantable unit with transcutaneous transmission of power and joint angle information was evaluated in a chronic dog. Silicone elastomers and surface primers, used in the implant packaging, provide biocompatibility and protection against corrosion. While long-term performance studies remain to be done with respect to implanted calibration and drift, the results from this study demonstrate the feasibility of a chronic implanted goniometer system.