Hip endoprosthesis for in vivo measurement of joint force and temperature

Friction between the prosthetic head and acetabular cup increases the tempe rature in hip implants during activities like walking. A hip endoprosthesis was instrumented with sensors to measure the joint contact forces and the temperature distribution along the entire length of the titanium implant. S ensors and two inductively powered telemetry units are placed inside the hi p implant and hermetically sealed against body fluids. Each telemetry unit contains an integrated 8-channel telemetry chip and a radio frequency trans mitter. Force, temperature and power supply data are transmitted at differe nt frequencies by two antennas to an external twin receiver. The inductive power supply is controlled by a personal computer. Force and temperature ar e monitored in real time and all data are stored on a video tape together w ith the patient's images. This paper describes the design and accuracy of t he instrumented implant and the principal function of the external system c omponents. (C) 1999 Elsevier Science Ltd. All rights reserved.