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Interview with Alister Hart

Listen to the full interview:

Who are you?

I’m Alister Hart, I’m a consultant orthopaedic surgeon and senior lecturer at Imperial College London.

What do you do?

My area of research is the biocompatibility of hip replacements.

What aspect of hip replacements are you looking into and why is it important?

I’m looking into the mechanism of failure of one particular type – a metal on metal hip replacement. Metal on metal hip replacement is a treatment for osteoarthritis. All hip replacements wear, but metal on metal hip replacements wear at the rate of one trillion nano particles per year, that is, one million nano particles per step and we walk one million steps per year.

Alister is supported by orthopaedic colleague John Skinner, clinical chemist Barry Sampson, immunologist Ferdinand Lali, engineers Philippa Cann and Richard Underwood, and particle biologist Jonathan Powell.

The research was funded by the Furlong Research Foundation, the British Orthopaedic Association and the British Hip Society.

Medical Case Study 1:
Longer Lasting Hip Replacements

Metal-on-metal hip replacement is a treatment for “wear and tear” arthritis (osteoarthritis) – one of the commonest diseases in the world. These hip replacements use cobalt chrome alloy for both bearing surfaces. They can be used to simply resurface both sides of the lining of the normal hip joint, which is called a hip resurfacing. The most commonly used type was developed 13 years ago in the UK and has been adopted world wide. One million people now have a metal-on-metal hip replacement. It was thought to be a solution to providing the everlasting hip for active and young patients with hip osteoarthritis but unfortunately we are now starting to realise that it has high failure rates. 

The failure is thought to be due to very small metal nano particles, released from the surface of the metal-on-metal hip, that cause an inflammatory reaction with fluid filled lumps up to 20cm in diameter.

How does Diamond enable you to find out more about these nano particles of metal being released?

Diamond enables us to map the metals within the tissue from patients with failed metal-on-metal hip replacements. It also enables us to characterise the type of metal within the tissue. Importantly it enables us to analyse the type of chemical in a situation that is as realistic as possible, that is without staining or without the use of a vacuum. It also allows us to analyse fresh frozen tissue sections with metals at quite low concentrations. These last advantages of the synchrotron beam line mean that we could not have achieved what we have found using other techniques.

Now you can visualise what metals are present in tissue, what have you found?

We have found that Chromium is the most abundant metal in tissue, which is surprising considering the implant is made of 60% cobalt, 30% chromium, and 7% molybdenum. We have also found that the type of chromium in the tissues is chromium (III) and is bound with phosphate.

What is the next step?

We can now feed human cells in a test tube with chromium phosphate and all of the other metal species that we’ve found present in the tissues from Diamond Light Source. If this recreates the same response that we see in humans, then we will have created a more valid biocompatibility test.  This could then go on to be used for testing other types of material and try to predict whether the same type of inflammation is likely to occur: before use in humans. This type of testing will hopefully accelerate new technologies rather than stifle them.

We hope to produce valid biocompatibility tests so that there is safer introduction of new materials to humans.

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