newcastle university crest extending prosthesis longevity through tribological understanding james...
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Newcastle University
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Extending prosthesis longevity through tribological understanding
James Lord&
Dr Tom Joyce
Newcastle University
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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
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• 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?
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• Total hip replacement
• Hip resurfacing
Types of hip prosthesis
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• 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
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• 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
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• Still many reported cases of early failure– Fracture– Infection– Metal debris
Metal-on-metal
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• Bearing surfaces• Many potential factors
– Manufacturing– Surgical– Patient
• Creates debris– Osteolysis– Metallosis
Wear
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• 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
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• 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
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• 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
-20-10
010
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-20-10
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Z
Volumetric wear
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Validation
Gravimetric wear volume (mm3)
Calculated wear volume (mm3)
Difference (%)
Unworn 0 0 -
1st volume removal
5.89 5.78 1.87
2nd volume removal
12.09 11.99 0.83
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• Surface coloured according to linear wear depth
• Histogram of depths
-0.07 -0.06 -0.05 -0.04 -0.03 -0.02 -0.01 0 0.01 0.020
50
100
150
200
250
Volumetric wear
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• Interferometry - occurs on the nanometre scale• Areas of interest informed by Matlab analysis
Wear scar
Transition zone
Unworn
Surface characterisation
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Qualitative characterisation
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Qualitative characterisation
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Qualitative characterisation
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• 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
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0
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0 20 40 60 80 100 120
Duration / months
We
ar
vo
lum
e /
mm
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Analysis – Wear volumes
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0 10 20 30 40 50 60 70 80 90
Implant duration / months
We
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lum
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mm
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ARMD
Early fracture
ARMD fracture
Analysis – Failure mode
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0 20 40 60 80 100 120
Duration / months
Wea
r vo
lum
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mm
3
36mm
BHR
Durom
Metasul
Analysis - Manufacturer
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0 20 40 60 80 100 120
Duration / months
We
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lum
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mm
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36mm
ASR
BHR
Durom
Metasul
Analysis - Manufacturer
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Analysis – Implantation angle
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R2 = 0.8906
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0 50 100 150 200 250 300 350
Combined volumetric wear / mm3
Blo
od
Co
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R2 = 0.9407
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0 50 100 150 200 250 300 350
Combined volumetric wear / mm3
Blo
od
Cr
ion
s
Analysis – In vivo data
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• 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
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• Data collection– Full data sets for current samples– New samples
• Statistical analysis– Significant factors affecting wear– Roughness values
• Other prostheses
What’s next?
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Questions?