A telemetry system for measurement of forces in massive orthopaedic implants in vivo

A wireless telemetry system is described for measurement of forces acting upon massive orthopaedic implants in man, to determine the load distribution in the fixation during routine activities and over long periods. The system comprises: the permanently implanted instrumented prosthesis, modified to enclose strain gauges and electronics, a single inductive link for powering the implant and telemetering the data, a UHF radio link, and real time data logging PC. The subject carries a small battery-powered energiser and microcontroller during measurements. Four instrumented prostheses have been implanted, and data recorded over several years. Hermetic sealing for the gauges and implanted instrumentation, and careful coil encapsulation techniques, have enabled data to be recorded over several years.