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DTI
MEASUREMENT, TESTING AND STANDARDS PROGRAMME
- PROJECT DEVELOPMENT Characterisation Of Fixation Systems Rationale: A joint replacement prosthesis has to provide not only an articulation function but also a secure attachment to the bones into which it is implanted. To date implant metrology has focused on the physical and mechanical properties and performance of the implant itself or its components and for which test methods and standards are now available. Whilst this has led to device improvements, in situ lifetime performance may now be determined by the time to failure of the device itself. Typically there is a sequence of events from loosening, movement, osteolysis (bone erosion) and consequent implant failure. Clinically relevant life predictive models and test methods are required to characterise current and innovative alternative fixation systems. Test methodology to support the establishment of performance standards to promote the development of improved device fixation systems and biomaterials is needed. Objectives: 1. To characterise orthopaedic fixation systems. 2. To develop models of fixation systems. 3. To develop test methods which determine the effect of device surface finish and surface coatings in cemented and uncemented fixation systems. 4. To analyse theoretical model systems incorporating device / cement interface, cement layer and cement / bone interface. 5. To measure the initial bone attachment and bulk physical properties of the cement, and the subsequent effects of bone re-modelling and changes in the cement / device interface. 6. To measure interfacial micro motions and the effects of geometry and accuracy of fit of the implant in the bone in cemented and uncemented systems. 7. To develop a methodology to assess movement and fixation failure in vivo. 8. To develop a metrology to predict life time performance of fixation systems. Industrial Contribution: Industrial contributions are expected in the form of prostheses and cement materials for evaluation and testing, plus advice and information about in-vivo performance of devices. The value of this is estimated at about £120,000. Cash contributions are also expected. Output Targets: The deliverables from this work will be: • two new test methods, and accompanying guides as to their use and application; • two models of fixation systems disseminated to 300 materials suppliers, prosthetic manufacturers, research and technical support organisations and orthopaedic surgeons; • one protocol for the assessment of movement and failure in vivo; • one review for industry characterising fixation systems; • two seminars attended by 100 representatives from materials suppliers, prosthetic manufacturers, research and technical support organisations and orthopaedic departments; • four scientific papers and articles for the medical press. Beneficiaries: The principal beneficiaries of this work will be the manufacturers of orthopaedic devices, the suppliers of surface coatings and cements for prostheses, orthopaedic surgeons involved in prosthetic surgery and the UK National Health Service through the improved performance of prosthetic joints. There will also be a significant improvement in the quality of life of UK citizens in need of prosthetic surgery.
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