ARTIFICIAL IMPLANTS

Improving our understanding of implant failures

All sorts of prosthetic devices are implanted every year into hundreds of thousands of people, including heart, vascular, bone and tissue implants. However, it is not unusual for such implants to be rejected or to malfunction. The causes are still poorly understood and existing reports to identify them are fragmented and disparate. COST Action 537, ‘Failure of the Explanted Prostheses Analysis’ (FEPA), collects and analyses data on implant failures to understand the causes and so improve the tools for human reconstruction.

Implantation of a cardiac defibrillator. ©Shutterstock Implantation of a cardiac defibrillator.
©Shutterstock
Comparison of the consequences of different types of biological and mechanical heart valves, particularly in terms of calcification. This research is carried out at the Heart Prostheses Institute of Zabrze (Poland) with the aim of improving the materials for heart valve implants. ©Zbigniew Nawrat Comparison of the consequences of different types of biological and mechanical heart valves, particularly in terms of calcification. This research is carried out at the Heart Prostheses Institute of Zabrze (Poland) with the aim of improving the materials for heart valve implants. ©Zbigniew Nawrat

If you are one of the world’s 60 million people with poor eyesight and wear contact lenses, then FEPA is of concern to you. The FEPA Action is part of the programme European Cooperation in the field of Scientific and Technical Research (COST). The aim of the Action is to determine more accurately the reasons why some prosthesis wearers are required to undergo a further operation to explant their devices. While it is a commonplace and problem-free task to replace the world’s annual 250 million used contact lenses, the same cannot be said of the 130 000 pacemakers, 100 000 breast implants or 90 000 hip replacement implants in the United States alone. “The implant failure rate is estimated to average 1%, rising to 3% for knee implants”, says FEPA coordinator Professor Rolando Barbucci. Of the 700 000 prosthetic devices implanted in the United States every year, some 7 000 will need to be explanted and reimplanted.

How can this failure rate be reduced and implants improved? According to FEPA researchers, the main problem stems from lack of information on the reasons for explanting. The fact that existing documentation on implant failures is fragmented, partial and disparate stands in the way of rational improvements in methods and materials. By forging a network of more than 40 research teams throughout Europe, FEPA collects the maximum amount of clinical data, analyses it and suggests possible ways for patients, medical teams and implant manufacturers to speed up the development of techniques and materials.

Analytical complexity

Widely diverse clinical practices make it difficult to establish a protocol for systematising the process of data collection and analysis on explant cases. Which materials are used for implants? How are operations carried out? Under what conditions are implants transported and prepared? Over what length of time are implant failures studied? Have the prostheses been implanted as life-saving devices (heart valves, etc), to improve the quality of life (ophthalmologic, orthopaedic) or for aesthetic reasons? All these questions make any analysis complex. The causes for explanting are just as many and varied, including faulty material, infection, and unforeseen interactions between the host and the implant or between tissues and material. This is compounded by the innovative nature of many of the products coming onto the market, for which long periods are required before suffi-cient feedback can be gained from clinical practice. This systematic lack of information obliges practitioners to fall back on their own experience or on “good practice” guides and booklets published by manufacturers. Nor does this lack of systematic studies on implant failure help manufacturers to improve their products and develop new more effective ones.

A systematic and exhaustive method

FEPA therefore aims to systematise the processes for evaluating clinical trials and to combine the results to provide reliable conclusions. The network includes scientists from a wide variety of disciplines such as materials science, chemistry, biomechanics, biology, pathology and of course surgery. Each group is in contact with a set of hospitals and sends back to FEPA clinical data on any explants performed. For each case, information is collected on the initial reasons for the implant, how long it was in place, the grounds for explanting and the type of prosthesis reimplanted, as well as on the patient’s medical history and on any chronic or psychological complications. The explanted prosthesis and the tissues collected are also subjected to systematic analysis. The results are reviewed and discussed to endeavour to determine the reason for the failure. Each case is archived in a database in accordance with a set of systematic criteria to ensure that similar situations can be compared.

When a sufficient amount of data has been collected, FEPA members focus on identifying the mechanisms responsible for each failure. The dynamic causing reactions between tissues and materials is examined, and analysis protocols are drawn up to evaluate interactions between the patient and the implant and to seek correlations between materials, mechanical behaviour, manufacturing methods and biological and clinical variables. The primary aim is to deduce hypotheses from these analyses in order to improve prosthesis materials and design by suggesting new alloys or polymers and new surface coatings.

Making the data accessible

The aim is to collect and analyse data and to draw up conclusions, not only to improve the procedures for establishing standards on the marketing of prosthetic devices (ISO standard), but also to provide quality assessment procedures for use by both practitioners and manufacturers. “By making available a collection of results from numerous hospitals scattered throughout several countries, by studying the causes of implant failure and suggesting possible ways to remedy them, FEPA provides bioengineers and implant manufacturers with useful information to help them optimise their artificial implants”, concludes Professor Rolando Barbucci. To this end, FEPA makes available not only its database of all the clinical cases studied but also a library containing all FEPA research. To help them to choose prosthetic devices, surgeons can obtain summaries of FEPA results from the library, and can also attend conferences and workshops held in Europe three to four times a year.

Staying at the cutting edge

Even though Professor Rolando Barbucci is still optimistic, citing recent research work based on the collection and analysis of 120 explanted units which had led to solutions for preventing all risks during the surgical removal of implanted heart valves, the advent of new materials poses a real challenge to FEPA. Recent advances in materials science have expanded the avenues of research and the new nanomaterials, while promising, represent a real challenge because their properties are still so little known. Although at present most orthopaedic prostheses are made from stainless steel or titanium, these two metals could soon be replaced, or at least coated, by a totally biocompatible diamond nanofilm. Although the diamond nanofilm is highly resistant and therefore likely to increase the life span of implants (a hip joint implant currently lasts between 15 and 20 years), it has the disadvantage of being rather rough and so attracting the proteins responsible for blood clotting. To remedy this shortcoming, researchers are now exploring the idea of covering the diamond nanofilm with a nanometric layer of hot ice, a nano-structure of crystallised water that remains in a solid state at body temperature.

Although FEPA research covers the incorporation of nanomaterials into prosthetic devices, it is still difficult to evaluate the use of such innovations. Time and feedback from clinical practice are lacking in a discipline where new materials are coming onto the market daily. As in numerous high-tech sectors, analysis, control, certification and standardisation procedures struggle to keep pace with rampant innovation.

François Rebufat


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