Analysis of failed metal on metal hip prostheses

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Analysis of failed metal on metal hip prostheses Powered By Docstoc
					      Extending prosthesis longevity through
            tribological understanding




                  James Lord
                      &
                 Dr Tom Joyce

Newcastle                                CREST
University
                                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                                    CREST
   University
                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                                              CREST
   University
                    Types of hip prosthesis

• Total hip replacement




• Hip resurfacing




   Newcastle                                  CREST
   University
                   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                                 CREST
   University
                           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                                            CREST
   University
                         Metal-on-metal

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




   Newcastle                                   CREST
   University
                           Wear

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




   Newcastle                      CREST
   University
                          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                                         CREST
   University
                     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                                      CREST
   University
                          Volumetric wear

• Co-ordinate data from CMM

                                  20
• Linear wear depths
                                  10




                              Z
  calculated
                                  0


• Wear volumes calculated          20
                                        10                                        20
   – From 0.71 - 134.22mm3                   0
                                                 -10                     0
                                                                             10

                                                                   -10
                                                       -20   -20
                                             Y                           X
   – Wear rates from 0.02 -
     5.77mm3/month




   Newcastle                                                                           CREST
   University
    Validation


              Gravimetric wear Calculated wear   Difference
               volume (mm3)     volume (mm3)         (%)
  Unworn             0                0              -
 1st volume        5.89             5.78            1.87
  removal
2nd volume         12.09            11.99           0.83
 removal




Newcastle                                                  CREST
University
                        Volumetric wear

• Surface coloured according
  to linear wear depth




• Histogram of depths          250



                               200



                               150



                               100



                               50



                                 0
                                -0.07   -0.06   -0.05   -0.04   -0.03   -0.02   -0.01   0   0.01   0.02




   Newcastle                                                                                              CREST
   University
                     Surface characterisation

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

                 Wear scar


            Transition
            zone



          Unworn



   Newcastle                                       CREST
   University
             Qualitative characterisation




Newcastle                                   CREST
University
             Qualitative characterisation




Newcastle                                   CREST
University
             Qualitative characterisation




Newcastle                                   CREST
University
             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                                      CREST
University
                               Analysis – Wear volumes

                     160

                     140
Wear volume / mm 3




                     120

                     100

                     80

                     60

                     40

                     20

                      0
                           0   20   40      60       80   100   120

                                     Duration / months


Newcastle                                                        CREST
University
                                    Analysis – Failure mode

                     160

                     140
Wear volume / mm 3




                     120

                     100
                                                                            ARMD
                     80                                                     Early fracture
                                                                            ARMD fracture
                     60

                     40

                     20

                      0
                           0   10   20   30   40   50   60   70   80   90

                                    Implant duration / months


Newcastle                                                                                CREST
University
                                  Analysis - Manufacturer

                    30


                    25
Wear volume / mm3




                    20
                                                                      36mm
                                                                      BHR
                    15
                                                                      Durom
                                                                      Metasul
                    10


                    5


                    0
                         0   20     40      60       80   100   120

                                     Duration / months



            Newcastle                                                   CREST
            University
                                    Analysis - Manufacturer

                     160

                     140
Wear volume / mm 3




                     120

                                                                       36mm
                     100
                                                                       ASR
                     80                                                BHR
                                                                       Durom
                     60
                                                                       Metasul
                     40

                     20

                      0
                           0   20      40     60      80   100   120

                                       Duration / months


Newcastle                                                                    CREST
University
                              Analysis – Implantation angle

               250




               200
Volume (mm3)




               150




               100




                50




                 0
                     0   10     20   30   40            50             60   70   80   90   100
                                               Inclination angle (0)




Newcastle                                                                                   CREST
University
                                                         Analysis – In vivo data

                300


                250
                                                         R2 = 0.9407
Blood Cr ions




                200


                150


                100


                50


                 0
                      0      50     100     150    200      250        300   350

                                                                  3                                80
                                  Combined volumetric wear / mm
                                                                                                   70
                                                                                                                                   R2 = 0.8906

                                                                                                   60




                                                                                   Blood Co ions
                                                                                                   50

                                                                                                   40

                                                                                                   30

                                                                                                   20

                                                                                                   10

                                                                                                   0
                                                                                                        0   50     100     150    200     250     300   350

                                                                                                                 Combined volumetric wear / mm3




                          Newcastle                                                                                                                     CREST
                          University
                                 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                                   CREST
University
                              What’s next?

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




   Newcastle                                 CREST
   University
             Questions?




Newcastle                 CREST
University

				
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posted:5/6/2011
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