Metal-on-Metal Hip Replacements: Solving The Uncertainties Dec 2011


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Jun 8, 2007
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Orthopaedic Research UK

Metal-on-Metal Hip Replacements: Solving The Uncertainties.

14th December 2011 The Royal College of Surgeons
[This seminar was organised to discuss the serious problem of MoM issues on a 'most senior' level with many other disciplines involved]​

1. Mr Keith Tucker, FRCS Norfolk & Norwich University Hospital, UL National Joint Registry
Epidemiology of the problem
Summarised the statistics and pointed out that the ASR was being revised at a rate of 12% annually. He added that these statistics were largely unreliable because there were many questions we should have been asking (via the Joint Registry) but didn’t because they hadn’t been flagged as problems and that it therefore behoves us to start collection such data immediately though answers wouldn’t be forthcoming until some years had elapsed, possibly about 20. We also needed to be converting current statistics into cases per 100 years to get a significant picture.​

2. Professor Michael Morlock Institute of Biomechanics, Hamburg University of Technology
Contribution of the stem taper to failure
Reported that revisions for THR MoMs for large diameter heads were increasing in comparison for HR of the same size with the exclusion of the ASR. He also posed the question was it to do with the taper of the trunion as these heads were initially designed for larger trunion and maybe there was a degree of toggle inside the fitting which lead to failure. He reported that in his cases where he had used a 36 or less mm head, there had been no problems whatsoever.​

3. Professor Anne Neville, BEng (1st Class Hons), PhD, Mechanical Engineering, University of Glasgow + University of Leeds
The Role of Corrosion
Professor Neville is a corrosion expert and has been looking into the role of corrosion in this issue. She said that while the metals in question do not corrode, they do wear and the wear particles corrode, also that metal ions are only released from the product of erosion. She also explained that there is a natural film of lubrication on the implant bearing surface and that this is an important factor because if it dissipates, then corrosion can occur.​

4. Dr Richie Gill, B.Eng, DPhil, University Lecturer in Orthopaedic Engineering and Group Head (Engineering) of the Oxford Orthopaedic Engineering Centre, University of Oxford
Pseudotumour after MoM hip resurfacing
Principal causes of revision are aseptic loosening and dislocation​

5. Mr David Langton North Tees and Hartlepool University Hospital
Patients with high wear
Cobalt or chrome ions: normal levels of 0.04% are not uncommon
Cobalt is excreted from the body very well​

6. Dr Paul Bills and Professor Liam Blunt, University of Huddersfield
Wear measurement of MoM hips
Measuring wear in retrieved devices differs significantly from measuring wear in simulations
There are many methods of measuring wear
Most have errors larger than those stated
Many different definitions of an “unworn” surface
It is difficult to define standards between small and large heads
The value and quality of research done is very variable and therefore not comparable in revisions
Wear occurs in the following sites:
the stem
outside the sleeve
the trunnion
inside the sleeve

the head
the cup​

7. Mr Tony Nargol, FRCS North Tees and Hartlepool University Hospital
When to revise an MoM hip
When to revise MoM hips: as soon as they show signs and/or symptoms but not necessarily both. Some patients have signs of wear, pseudotumours, loosening and ‘fluid’ which might actually be liquefied fat. All patients should be referred sooner rather than later. Emphasised “pick them up early”​

8. Mr Ben Bolland, FRCS Southampton General Hospital
Modular versus resurfacing
MARS MRI or ultrasound scanning
MoM problems are often incorrectly diagnosed psoas tendonitis
Ion tests above 100ppb should be considered as abnormal​

9. Professor Tim Briggs, MB BS (Hons), MChOrth, FRCS (Ed.), FRCS (Eng.) Royal National Orthopaedic Hospital
The clinical relevance of chromosomal abnormalities
Revisions have increased in the last 6 years
When both hips are done non-sequentially, it is often the second hip that fails and this might be because the extra presence of metal tips the individuals tolerance over the edge of normal
Normal cobalt and/or chrome ion levels don’t always indicate absence of problems
Increased wear has more often been observed in the tapers (trunion) than the head or cup
ASR has the highest failure rate
Females would seem to be suffering a higher revision rate than males
Large heads have higher revision rates than smaller heads
Wear and motion at the trunion leads to corrosion​

10. Dr Patrick Case, University of Bristol
The systemic effects or risks of cancer
(This paper was somewhat beyond my level of comprehension but the following discussion raised the following issues)
It is being suspected that high ion levels might be responsible for issues in
- heart (cardiomyopathy)
- skin problems
- ophthalmic issues
- hearing problems
- kidney function
- liver function
- cognitive impairment
- suppressed immune system
- thyroid issues
- and many other areas
- reversal of such symptoms have appeared to be reversed after revision to a non-MoM device indicating the body is very capable of dealing with elevated ions
- it was suggested that many of these we don’t know about because the questions have never been posed. That we now need to refine our data collection and start collecting such data but results won’t be available for another 20 years or more!​

11. Professor Alfons Fischer, University Duisburg-Essen
The role of metallurgy
This speaker emphasized the fact that in 80% of successful revisions, the need for them cannot be adequately explained
It was then described how the polishing of the articular areas of the device creates a chemical film on the surface only nanometres thick which maintains the robustness of the metal
MoM reaction is actually a reaction of the two chemical films on the opposing devices. When this reaction destroys the film, then the bearing is very quickly down into the metal itself. This would still only be nanometres of depth into the metal.
The hardness phase of metal is influenced by the size range plus the shape plus the distribution of particles.​

12. Mr Derek McMinn, FRCS, The McMinn Centre, Birmingham
Complications of THR vs HR
This paper was a summary of the ‘no problem’ status of his clinic.
It would seem that this surgeon has not experienced any of the issues currently raising concern.
Go figure!​

13. Professor Markus Wimmer Rush University, Chicago
The variability of wear
Provided significant data regarding wear of different devices, materials
The presence of the chemical film was also mentioned in that it protects the metal against corrosion but also that it is not stable​

14. Mr Raghu Raman, MRCS, MRCS (Ed), FRCS (Tr&Orth) Hull and East Yorkshire Regional Arthroplasty Centre, Hull
Defined ways of diagnosing issues like fluid collections, in xrays
Cited that ‘fluid’ often turned out to be very viscous or even semi-solid material, the result of liquefied muscle fat​

15. Dr Keshthra Satchithananda, BDS, FDSRCS, MBBS, FRCS, FRCR London Bridge Hospital
MRI scanning
Defined the MARS (Metal Artefact Suppression Technique) MRI protocol for viewing metal devices

16. Mr Steve Jones, BSc(Hons), MBBCh, MRCS(Eng), MSc(Orth Eng), Cardiff University
Blood metal ions levels
Went over ground previously covered but in some technical detail
Cited that for him, the hip had to be a ‘forgotten hip’ to be okay​

17. Mr David Beverland, FRCS MB BCh Queens University Hospital, Belfast
The Belfast follow-up protocol
This speaker has done a lot of work and a lot of revisions on his patients
He estimates that only 50% of ASRs have been seen thus far​

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