Concept, design and fabrication of smart orthopedic implants

Extensive clinical experience has been built up using orthopaedic implants instrumented with strain gauges connected to a Wheatstone bridge by means o f percutaneous leads. This research showed the medical relevance of the mon itoring of the deformation of implants as a powerful tool to evaluate nursi ng and rehabilitation exercises, for tracing dangerous overloads and antici pating implant failure and also to observe the healing process. The IMPACT 3500 project focuses on the instrumentation of femoral implants with on boa rd sensors: regular Benoist-Girard implants have been modified. to contain a 'sensing cell', and thoroughly tested in vitro and in vivo. The implant d eformations are measured with resistive strain gauges, and the signal is tr ansferred to a personal computer for processing and display, via a hard wir ed connection, or via a telemetry system. Two fully implantable wireless de signs, called Linkstrain and Sealstrain, are powered from the outside by ma gnetic induction. As Sealstrain contains the whole telemetric system in its cavity, the highest miniaturization was required; this seriously deteriora tes the efficiency of the inductive power link. (C) 2001 IPEM. Published by Elsevier Science Ltd. All rights reserved.