New methods for the evaluation of fatigue behaviour of bone-implant systems

Abstract

The use of functional internal implants is widespread in the clinical therapy of fractures. One of the problems associated with internal implants is failure of the implant. The present study presents a methodology to obtain a medically relevant characterization of implants regarding implant failure. A fatigue test is carried out on systems of implant and bone, the sensor system can flexibly be adjusted to different systems and different analyzed properties. Characteristic values are obtained by computer - aided analysis of the measured values. Especially the evolution of the "permanent deformation" in combination with "Stiffness" during the fatigue sequence allows a medically realistic characterization of the long-time fatigue-behaviour of the implant. Three case studies were carried out to show practicability of the study:<br />therapy of extra-articular fractures of the distal tibia with intramedullary nailing and two further studies concerning the treatment of intra and extra - articular fractures of the distal radius using volar plate osteosynthesis. The analysis covers different implant designs and different types of screwing. The sensibility of the method to the factor synthetic bone material is assessed. Limits and drawbacks of the studies are evaluated and advice for further improvement of the method is given. Essential relevance was substantiated for the chose of bone material. The major advantages of this method are the universal applicability to different kinds of systems, the comprehensive exposition of properties and the possibility of flexible expansion in future use.<br />