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
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
Newcastle
University
CREST
Types of hip prosthesis
• Total hip replacement
• Hip resurfacing
Newcastle
University
CREST
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
Newcastle
University
CREST
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
Newcastle
University
CREST
Metal-on-metal
• Still many reported cases of early failure
– Fracture
– Infection
– Metal debris
Newcastle
University
CREST
Wear
• Bearing surfaces
• Many potential factors
– Manufacturing
– Surgical
– Patient
• Creates debris
– Osteolysis
– Metallosis
Newcastle
University
CREST
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
Newcastle
University
CREST
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
Newcastle
University
CREST
Volumetric wear
• Co-ordinate data from CMM
Z
• Linear wear depths
calculated
20
10
0
• Wear volumes calculated
– From 0.71 - 134.22mm3
– Wear rates from 0.02 5.77mm3/month
Newcastle
University
20
10
20
10
0
0
-10
Y
-20
-10
-20
X
CREST
Validation
Gravimetric wear Calculated wear
volume (mm3)
volume (mm3)
Difference
(%)
Unworn
0
0
-
1st volume
removal
5.89
5.78
1.87
2nd volume
removal
12.09
11.99
0.83
Newcastle
University
CREST
Volumetric wear
• Surface coloured according
to linear wear depth
• Histogram of depths
250
200
150
100
50
0
-0.07
Newcastle
University
-0.06
-0.05
-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
CREST
Surface characterisation
• Interferometry - occurs on the nanometre scale
• Areas of interest informed by Matlab analysis
Wear scar
Transition
zone
Unworn
Newcastle
University
CREST
Qualitative characterisation
Newcastle
University
CREST
Qualitative characterisation
Newcastle
University
CREST
Qualitative characterisation
Newcastle
University
CREST
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
Newcastle
University
CREST
Analysis – Wear volumes
160
Wear volume / mm
3
140
120
100
80
60
40
20
0
0
20
40
60
80
100
120
Duration / months
Newcastle
University
CREST
Analysis – Failure mode
160
Wear volume / mm
3
140
120
100
ARMD
Early fracture
80
ARMD fracture
60
40
20
0
0
10
20
30
40
50
60
70
80
90
Implant duration / months
Newcastle
University
CREST
Analysis - Manufacturer
Wear volume / mm
3
30
25
20
36mm
BHR
15
Durom
Metasul
10
5
0
0
20
40
60
80
100
120
Duration / months
Newcastle
University
CREST
Analysis - Manufacturer
160
Wear volume / mm
3
140
120
36mm
100
ASR
BHR
80
Durom
60
Metasul
40
20
0
0
20
40
60
80
100
120
Duration / months
Newcastle
University
CREST
Analysis – Implantation angle
250
Volume (mm3)
200
150
100
50
0
0
10
20
30
40
50
60
70
80
90
100
Inclination angle (0)
Newcastle
University
CREST
Analysis – In vivo data
300
R2 = 0.9407
200
150
100
50
0
0
50
100
150
200
250
Combined volumetric wear / mm
300
350
3
80
R2 = 0.8906
70
Blood Co ions
Blood Cr ions
250
60
50
40
30
20
10
0
0
50
100
150
200
250
300
350
Combined volumetric wear / mm3
Newcastle
University
CREST
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
Newcastle
University
CREST
What’s next?
• Data collection
– Full data sets for current samples
– New samples
• Statistical analysis
– Significant factors affecting wear
– Roughness values
• Other prostheses
Newcastle
University
CREST
Questions?
Newcastle
University
CREST