The implantation of transducers in the human body leads to technological constraints which are difficult to solve since biological tissues constitute an extremely hostile environment. The project envisages the realisation of new "intelligent" orthopaedic implants sensitive to deformation and using a telemetric link. The transmitted information is of great value to judge the degree of rehabilitation of a fracture, and will assist the standard x-rays which in most cases proved to be unreliable.
The most important packaging bottle necks have already been solved during the project: the ceramics-to-metal joining technology is available and the laser welding technology is fully optimized. The u-metal coil core and a double sided hybrid are still to be manufactured, but these are straight applications of available technologies. The sensor and the interface chips are ready. The powering circuits, both internal and external, are available right now, but the frequency is to be scaled down from 1MHz to approximately 10kHz. This means that the frequency dependant components are to be recalculated. The powering coil set is fully conceived.
This concept is now to be worked out into a dedicated design. Inside the recess comes the monitoring electronics to handle the sensor signal, as well as the high frequency transmitter for the data communication. Both are placed on thick film hybrid circuits to cope with the demand for miniaturization. These circuits are trimmed to each individual implant.
The aim of the impact project is to characterize the mechanical situation of an osteosynthesis, postulating that in normal conditions rehabilitation can take place when the implant is submitted to loads unable to result in fatigue failure. The conclusion of our clinical experience only deals with percutaneous data acquisition, which is not the final goal of the project, but allowed to define and to quantify important parameters which revealed to be of the utmost importance for some tasks concepts. The definition of a new generation of fracture implants and the clinical evaluation of the value of the impact concept are determined. The technique of monitoring, when available, is now fully accepted in the Department at Hopital Erasme and used routinely by the surgeons and the physiotherapists. The loading of the implanted system is imposed by the activities of the patient, however, many factors are responsible for the zero drift of a strain gauge system. The biological environment imposes very specific conditions as regards the electrical insulation referred as a packaging problem.
A marketable product will be to make the system user-friendly, for the envisaged customer group: surgeons, nurses and physiotherapist. The recorded deformation must be compatible with a safe deformation of the implant. A receiver stage, directly connected to the monitoring computer, is tuned to capture the data and offer it to the computer in the correct format.
This project is an original approach to the problem of mechanical failure of orthopaedic implants. The success of the implantation of miniaturised electronics on orthopaedic implants is the availability of biocompatible materials for encapsulation (packaging). The objectives of the project are:
-to significantly reduce the failure rate of high risk osteosyntheses and to decrease the severe complications resulting from such failure e.g. social and financial impacts;
-to develop a tool for assessing new orthopaedic implants including joint replacement;
-to develop implantable miniaturised telemetry system.