An implantable transducer for two-degree-of-freedom joint angle sensing

An implantable joint angle transducer (IJAT) was developed for chronic use with upper extremity functional neuromuscular stimulation (FNS) neuroprostheses. The IJAT uses a permanent magnet surgically implanted in one bone, and an array of Hall effect sensors surgically implanted in the opposing bone. Titanium encapsulation protects the magnet, sensors, and support electronics, and secures the packages in the bone. The IJAT provides command control or feedback signals from mid-sized two-degree-of-freedom (2-d.f.) joints. IJATs were implanted using a chronic in-vivo dog model to demonstrate the feasibility of implantation and periodic measurement techniques, and to validate modeling techniques used for prediction of function and calibration. The flexion resolution ranged from 0.4° to 3.0°. The maximum deviation from a linear response was 9°. The resolution and linearity depend on several transducer and joint geometry parameters, and can be predicted pre-implantation and calibrated post-implantation