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The University of Southampton

Research project: Better methods to measure wear of hip implants

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To make hip implants that last longer.

To better determine what is going wrong in implants, better methods are needed to measure wear. Correctly measuring the material loss caused in wear simulators is difficult. Traditionally this is done by what is called the gravimetric method; after so many cycles the implants are taken out of the machine and weighed. However, in many hard-on-hard implants such as metal-on-metal or ceramic-on-ceramic, the amount of wear produced can be very small, on the order of only .000 2 grams after hundreds of thousands of cycles of wear. The implants themselves can be relatively heavy weighing 150 to 200 grams. Detecting that small amount of weight change in a mass that large is operating at the very limit of what the best commercial balances can measure. Even such small amounts of wear can have catastrophic effects on patients; producing adverse tissue reactions, resorption of bone resulting in implant loosening and even pseudotumors. Simultaneously with the validation study we will be comparing three alternative methods to measure wear loss by surface analysis. They are coordinate measuring machine, CMM; roundness machine; and optical light profilometry with the commercial RedLux system.

as shown in a RedLux optical scan
Wear scar on a femoral head

We now have some preliminary data that indicates that the RedLux optical method may be able to measure the amount of wear as accurate as the old method but with more critical information on where the wear is occurring along with its depth and area profiles in high resolution.

Related research groups

national Centre for Advanced Tribology at Southampton (nCATS)
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