LifeLongJoints aims to deliver next-generation, functional Silicon Nitride coatings for articulating surfaces and interfaces of total hip replacements (THR) to produce longer lasting implants.
It is anticipated that these coatings will significantly reduce the risk of implant failure associated with wear, synergistic wear/corrosion processes and the resultant debris release as well as provide significant economic and societal benefit to Europe and its citizens.
The highly significant economic and patient issues around early failure in metal-on-metal total hip and resurfacing replacements have been brought sharply into focus within the public media, for instance the BBC reported Metal-on-metal hip replacements ‘high failure rate’. Similarly the scientific and clinical communities have become acutely aware of this detrimental issue and are entering a debate which focuses on alternative materials and designs for replacement systems. Added to these issues are growing concerns from regulatory authorities on how to effectively test these devices before they are implanted into patients, as the current spate of metal-on-metal failures appear not to have come to light with current assessment methodologies.
More generally, other types of total joint replacements have been a remarkable success and provide many patients relatively pain-free lives with improved mobility and social functioning. However, there are still a considerable number of revision procedures that take place, annually, as a result of both the sheer volume of artificial joints implanted and low but significant failure rate of between 3% and 10% at 10 years. Kurtz et al (2009) predicted that in the US failures of artificial hip and knee joints would exceed 100,000 patients per year, which equates to an economic burden of over €1bn/annum. Stargardt (2008) reports that Europe’s healthcare systems are showing similar signs of economic stress. These observations suggests that improvements in implants performance are needed in two critical areas:
- Artificial joints need to survive longer (extending prosthesis lifetimes) and
- Replacement joints need to be more robust against the variability encountered in vivo (few failures at the early or mid-life time points)
This resilience must overcome variability in the prosthetic performance that arises from surgical technique (for instance, implant position), pathology, and patient characteristics, all of which have been shown to impact on the rates of failure.
The majority of failures beyond 3-5 years are largely the result of wear and the reaction of the body to the particles and corrosion products released during this process. The table below summarises the causes of loosening and related wear in total joint replacements. Past research has focused largely on reducing the overall levels of wear. However, if we accept the premise that wear cannot be eliminated entirely and is an inevitable consequence of motion at an interface, then alternative routes to improving both the long-term survival and resilience need to be sought to allow a greater proportion of patients a trouble-free existence following surgery.
| Material Debris
Size |
Pathology |
| Ultra-high-molecular-weight polyethylene (UHMWPE) particles:
Predominately 0.1 to 1 mm |
Induce predominantly inflammatory responses leading to osteolysis, aseptic loosening, and failure |
| Cobalt chrome (CoCr) particles
Predominately < 0.05 mm |
Two types of pathology can result from metal-on-metal hip prostheses;
Responses in (ii) are linked to tissue necrosis and formation of pseudotumours.
|
Our solution to the demanding issue of wear related failure is to produce a novel bearing coating utilising silicon nitride (for use at bearing surfaces and modular junctions as in the head-neck taper) that combines the following attributes:
- Uniquely this project will consider wear debris that are soluble and reduce the propensity for an inappropriate biological response once these particles are released into the joint space.
- Τhe release of ions that have been shown not to be cytotoxic when from either the coating or debris.
- An extremely low wearing coating that is comparable to contemporary bulk ceramic bearing systems (which can fail catastrophically and are expensive) and significantly better than rates of wear observed in metal-on-metal articulations (which also release deleterious cytotoxic debris and ions).
This combination of attributes moves away from focusing on developing extremely low wear systems in isolation, to one that takes a more holistic view of wear in THR looking at all stages in the failure process. If successful, these improved wear characteristics will lead to
- improved therapeutic outcomes through longer lasting and more robust implants and
- overall improvements in the quality of life of the patients
through reductions in implant failures and subsequent revisions.
Objectives
The programme of research will produce a biocompatible, low-wearing silicon nitride coating, functionally tested utilising cutting edge techniques with a view to preparing the necessary regulatory information, as appropriate.
- Development and characterisation of novel wear-resistant silicon nitride-based coatings for both articulating and non-articulating surfaces;
- Development of advanced simulation methodologies, in vitro, together with the dissemination of new guidance documents and standards for the functional assessment of novel silicon nitride coatings;
- Production of in silico tools for the prediction of wear, which reflects the variability of patient and surgical inputs with which to evaluate coating performance;
- Production and pre-clinical testing of a series of prototype devices in each of the scenarios for functional assessment and production evaluation;
- Finalise manufacturing scale-up through translation of the coating technology from a research to the industrial environment;
- Delivery of the necessary in vivo data through the use of applications-specific experiments to support the use of the coating in terms of cytotoxicity and joint functionality, and
- Deliver the necessary regulatory evidence to an advanced stage.
The total project funding for LifeLongJoints is in excess of €18M with the European Commission providing €13.317M and the remainder being contributed by the consortium members themselves. The consortium comprises 14 partners of which seven are publically funded organisations, which includes six Universities and one state-sponsored hospital, and an equal number of private sector organisations, of which one is a commercial health care provider. A real strength of the consortium is that they have numerous, pre-existing collaborations including Pan-European projects (e.g. SpineFX, VPHOP and an ERC advanced fellowship, FUNMAT) as well as national large scale programmes of research (see figure below). These linkages reduce both the risk and the learning curve associated with the development of this new initiative.
The management structure of the LifeLongJoints project has been designed to be commensurate with the size, duration, work package structure and scope of this highly ambitious project. The roles and responsibilities of the component committees are detailed in diagram below. The decision-making structures and tasks of the Consortium, and the responsibilities of Partners regarding the financial and scientific management of the project are formally enshrined in the LifeLongJoints Consortium Agreement (CA), which also sets out clear exploitation (use of knowledge), dissemination and regulatory plans.
