Analysis of failed metal.ppt

Newcastle University CREST Extending prosthesis longevity through tribological understanding James Lord Dr Tom Joyce 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 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? Total hip replacement Hip resurfacing Types of hip prosthesis 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 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 Still many reported cases of early failure Fracture Infection Metal debris Metal-on-metal Bearing surfaces Many potential factors Manufacturing Surgical Patient Creates debris Osteolysis Metallosis Wear 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 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 Co-ordinate data from CMM Linear wear depths calculated Wear volumes calculated From 0.71 - 134.22mm3 Wear rates from 0.02 - 5.77mm3/month Volumetric wear Validation Gravimetric wear volume mm3 Calculated wear volume mm3 Differen