Extending prosthesis longevity through tribological understanding

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Extending prosthesis longevity through
tribological understanding

• James Lord
• Dr Tom Joyce

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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
• Whats next?
• Questions

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What are hip prostheses?

• 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

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Types of hip prosthesis

• Total hip replacement
• Hip resurfacing

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Metal-on-polyethylene

• 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

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Metal-on-metal

• 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

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Metal-on-metal

• Still many reported cases of early failure
• Fracture
• Infection
• Metal debris

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Wear

• Bearing surfaces
• Many potential factors
• Manufacturing
• Surgical
• Patient
• Creates debris
• Osteolysis
• Metallosis

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My work

• 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

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Volumetric wear

• 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

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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

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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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Volumetric wear

• Surface coloured according to linear wear depth
• Histogram of depths

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Surface characterisation

• Interferometry - occurs on the nanometre scale
• Areas of interest informed by Matlab analysis

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Qualitative characterisation
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Qualitative characterisation
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Qualitative characterisation
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Quantitative characterisation

• Unworn surface
• Ra 0.019µm
• Rms 0.039µm
• Transition zone
• Ra 0.028µm
• Rms 0.063µm
• Wear scar
• Ra 0.200µm
• Rms 0.280µm

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Analysis Wear volumes
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Analysis Failure mode
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Analysis - Manufacturer
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Analysis - Manufacturer
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Analysis Implantation angle
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Analysis In vivo data
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Analysis

• 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

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Whats next?

• Data collection
• Full data sets for current samples
• New samples
• Statistical analysis
• Significant factors affecting wear
• Roughness values
• Other prostheses

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Questions?