Newcastle University CREST Extending prosthesis longevity through tribological understanding James Lord & Dr Tom Joyce

Newcastle University CREST Contents What are hip prostheses? –Types –Metal-on-polyethylene vs. metal-on-metal Wear My work –Linear and volumetric wear –Surface characterisation –Analyses of important factors What’s next? Questions

Newcastle University CREST Attempts to replace the damaged hip joint with long-lasting biocompatible materials Reduce pain and restore function Can be traced back 120 years Traditionally metal-on-polyethylene articulation More recent shift to metal-on-metal articulation What are hip prostheses?

Newcastle University CREST Total hip replacement Hip resurfacing Types of hip prosthesis

Newcastle University CREST Charnley – 1960s & 1970s Survivorship can be around 80% after 20 years Reported cases of early failures Failures greater in younger patients –Kim, 2003 Polyethylene debris linked to osteolysis Metal-on-polyethylene

Newcastle University CREST MoM shown to produce smaller particles and less overall volumetric wear than MoP Machinability Generally good short-term results –Treacy et al, 2005 – 98% at 5 years –Khan et al, 2009 – 95.7% at 8 years Long-term studies less common Metal-on-metal

Newcastle University CREST Still many reported cases of early failure –Fracture –Infection –Metal debris Metal-on-metal

Newcastle University CREST Bearing surfaces Many potential factors –Manufacturing –Surgical –Patient Creates debris –Osteolysis –Metallosis Wear

Newcastle University CREST Extending prosthesis longevity through a reduction in wear Study of 150 retrieved components Volumetric wear of retrieved components Wear characterisation Influencing factors –Manufacturing –Surgical –Patient My work

Newcastle University CREST Co-ordinate measuring machine recommended by international standards Measures 3-dimensional Cartesian co-ordinates Ruby-tipped contact stylus 72 line scans ~2000 measured points Self-centring scans Some analysis Volumetric wear

Newcastle University CREST Co-ordinate data from CMM Linear wear depths calculated Wear volumes calculated –From mm 3 –Wear rates from mm 3 /month Volumetric wear

Newcastle University CREST Validation Gravimetric wear volume (mm 3 ) Calculated wear volume (mm 3 ) Difference (%) Unworn00- 1 st volume removal nd volume removal

Newcastle University CREST Surface coloured according to linear wear depth Histogram of depths Volumetric wear

Newcastle University CREST Interferometry - occurs on the nanometre scale Areas of interest informed by Matlab analysis Wear scar Transition zone Unworn Surface characterisation

Newcastle University CREST Qualitative characterisation

Newcastle University CREST Qualitative characterisation

Newcastle University CREST Qualitative characterisation

Newcastle University CREST Unworn surface –Ra: 0.019μm –Rms: 0.039μm Transition zone –Ra: 0.028μm –Rms: 0.063μm Wear scar –Ra: 0.200μm –Rms: 0.280μm Quantitative characterisation

Newcastle University CREST Analysis – Wear volumes

Newcastle University CREST Analysis – Failure mode

Newcastle University CREST Analysis - Manufacturer

Newcastle University CREST Analysis - Manufacturer

Newcastle University CREST Analysis – Implantation angle

Newcastle University CREST Analysis – In vivo data

Newcastle University CREST Wear volumes/rates –Failure modes –Different manufacturers –Implantation angle –Correlation to in vivo data Roughness values –Low/high wear samples –Self-polishing Tribology –Lubrication regime Analysis

Newcastle University CREST Data collection –Full data sets for current samples –New samples Statistical analysis –Significant factors affecting wear –Roughness values Other prostheses What’s next?

Newcastle University CREST Questions?