Battery-Less Wireless Instrumented Knee Implant

Over 400,000 total knee replacement procedures (TKR) are performed annually in the United States. This paper focuses on the development of a battery-less wireless instrumented tibial tray for performance feedback in TKR implants. The proposed instrumented tibial tray is powered internally by an integrated piezoelectric energy harvesting system. Energy is harvested during the walking of the patient when forces are exerted on the tibial component. The sensors and wireless electronics are entirely powered from the harvested energy. This tibial tray is also instrumented with capacitive force sensors and an ultra low-power method to measure the capacitive force sensors. A bench top test rig is developed for testing the battery-less wireless knee replacement implant. For a person with a body weight of 55 kg, the energy harvesting system can fully charge the storage capacitors in 11 steps and can harvest an average of 1051 μJ per step. To power the force measurement system for ten seconds and to transmit the data, the piezoelectric energy harvesting system must be charged before the force measurement process is initiated by a minimum of 11 steps and a minimum of two steps must be taken during the force measurement process. During the force measurement process, each force sensor is sampled at a frequency of 10 Hz for ten seconds; thereafter, all of the data is transmitted to the RF base station. The resulting capacitive force sensors adequately represented cyclic loads; however, the sensors demonstrated some issues with repeatability.