Not all that’s new and shiny is good for healthcare
BMJ 2011; 343 doi: https://doi.org/10.1136/bmj.d7997 (Published 08 December 2011) Cite this as: BMJ 2011;343:d7997
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An editorial reflecting a review of different bearing couples in hip arthroplasty(1) sponsored by the FDA should be illuminating. Instead, significant errors render its conclusions perverse. “Implantable hip devices” is a new term to the arthroplasty literature, sounding all-encompassing. But the authors make no attempt to distinguish total hip arthroplasty (THA) from hip resurfacing arthroplasty(HRA), and make no mention of this safer, more conservative and more successful form of arthroplasty.
By failing to be discriminate between types of arthroplasty, and the fine detail of head size, type of trunion, exact type of bearing material, and manufacturing technique, the paper myopically and determinedly mixes the results of devices that have been withdrawn with those that are still in use with long term excellent function. This ‘bundling’ of devices into classes may make life easy for legislators (and editors) but is the opposite of being a discriminating consumer. They then repeat the nostrum of describing as ‘conventional’ any combination of metal on polyethylene bearing couple, failing to notice that the large metal heads against new thinner plastics bear scant resemblance to the bearings of the past. They describe as ‘alternative’ the hard bearings such as ceramic-on-ceramic and metal-on-metal, some of which have been successfully implanted for decades in successful combinations allowing patients to return to high levels of activity without fear of early revision.
When choosing outcome measures, the editor should also reflect on an issue that most patients care most about: mortality. THA has long been associated with a substantially higher mortality than HRA, both in our own (3)and other national registries(4). Instead the paper cited reports on the clinical scores developed to demonstrate the difference between an arthritic patient awaiting surgery and the postoperative state. Such scores typically have over 50% of hips achieving perfect or near perfect scores following surgery(22), so they are not capable of discerning excellent from good results. No amount of meta-analysis of papers using the same limited metrics lifts this ceiling.
In a paper to be presented to the American Academy of Orthopaedic Surgeons in 2012, we confirm what most patients with a well designed and made hip resurfacing have observed: that their function is substantially superior to patients whose hips have been replaced. In patients matched for age, sex, BMI, severity of disease and leg length, by using an instrumented treadmill, we have observed a 9% superiority in top walking speed among other variables (table 1).
This substantial functional superiority cannot be detected by scores designed for THA. These same scores are also unable to detect the higher level function over many years that is achievable with a ceramic on ceramic bearing: by warning people from taking exercise as John Charley did, surgeons using his metal on plastic bearings have a subtle but important impact on the quality of life, missed by hip scores: the patients don’t exercise for fear of premature revision, while ceramic bearings liberate people to do as they please knowing that excessive wear is unlikely to be cause failure.
Meta-analyses are blunt instruments. By focusing on insensitive outcome measures, and a myopic bundling of all bearings into ‘classes’, ignoring the essential details, the authors betray a particular mindset that has been repeated by the editor. Substantial improvements in life expectancy and quality of life are obtainable, using well proven devices of particular brands. This should interest the discriminating consumer, if not the FDA.
1. Sedrakyan A. Comparative assessment of implantable hip devices with different bearing surfaces: systematic appraisal of evidence. BMJ. 2011.
2. Wise J. NHS publishes new data on patient reported health outcomes. BMJ. 2010.
3. Porter Mea. Risk of death following hip arthroplasty. 2011; Available from: http://www.njrcentre.org.uk/NjrCentre/Portals/0/Documents/figure3.6.pdf.
4. Lie SA, Engesaeter LB, Havelin LI, Gjessing HK, Vollset SE. Mortality after total hip replacement: 0-10-year follow-up of 39,543 patients in the Norwegian Arthroplasty Register. Acta Orthop Scand. 2000 Feb;71(1):19-27.
Competing interests: No competing interests
Re: Not all that’s new and shiny is good for healthcare
We thank Mr. Cobb for a response and critique of our paper titled ‘Comparative assessment of implantable hip devices with different bearing surfaces: systematic appraisal of evidence’(1). However, the author failed to note important exclusion criterion for our study; we focused our evidence appraisal on conventional hip replacement and hip resurfacing has been excluded. This is clearly described in the methods section of our paper. We also would like to mention that the author’s view on hip resurfacing devices is not universally shared and resurfacing seems to work best in very selected populations(2).
Other factors that Mr. Cobb considered important such as head size, type of trunion and manufacturing techniques represent separate research questions and require focused investigations. For example, whether larger head sizes have advantage over smaller size (with or without metal-on-metal bearing or any other bearings) in terms of revision occurrence or functioning requires systematic evidence appraisal of all available evidence related to all bearings, type of trunions and manufacturing techniques. We do agree that some of the current bearings including larger heads with cross-linked polyethylene might have advantages over non cross-linked polyethylene(3). This question was also a subject to separate evidence synthesis investigation with meta-analyses(3). With the same line of thinking the author might reject the conclusions of any step by step systematic investigation of evidence just because it is not all inclusive or product specific. If there is an interaction between the type of bearing, the head size or type of trunion then this can be investigated in a large multicenter/multinational registries such as International Consortium of Orthopedic Registries (ICOR) that we mentioned in our manuscript. Inclusion of any variable will be subject to reaching consensus by leading registry researchers. This is certainly beyond the scope of the evidence review that summarized up to date available evidence related to various bearing surface. In fact, attempting to lump all these questions together is unnecessary complicated thinking that plagues orthopedic device research today.
We agree with the author that there is a need to design instruments or methods to overcome the limitations of current functioning measurements and discuss minimally important differences in orthopedic surgery (both change from baseline and comparative purposes). However, the surgeons and researchers that investigated implants with different bearings chose to rely on Harris Hip Score and other well known instruments. It is also clear from published evidence that the functional outcomes, that some might claim favor alternative bearings such as newer metal-on-metal bearings are not different from the well tested metal-on-polyethylene bearings. This is an important conclusion as it is based on all available evidence published up to date.
The issue of ‘class effects’ vs individual product effects is also important for a discussion. This has been an important issue for investigators, clinicians and regulators from the outset and is not specific to orthopedics. Are all drug eluting stents the same? Are all tissue cardiac valve implants the same? are all hip resurfacing devices that the author favors the same? The answer will depend on the ability to generalize (lumpers vs splitters) and should be subject to thorough investigation. There is certainly enough evidence related to metal ion release, sensitivity and tissue necrosis to conclude that these effects represent a class effect for all metal-on-metal devices. And the burden to prove otherwise should be on manufacturers, investigators and surgeons. Particularly those who get their products based on ‘non-inferiority’ but claim ‘potential for’ superiority when marketing or using these individual products. These studies needs to be large enough, well designed and comparative to convince the clinicians, researchers and regulators.
It is not clear how these major and paradigm based issues can serve as a critique of the systematic review and meta-analysis that serves a very different purpose; combine underpowered but substantially similar(homogenous) clinical studies, particularly in hard to study settings, to improve statistical power and ability to make better conclusions.
1. Sedrakyan A. Comparative assessment of implantable hip devices with different bearing surfaces: systematic appraisal of evidence. BMJ. 2011.
2. Prosser GH, .. Graves SE, et al. Outcome of primary resurfacing hip replacement: evaluation of risk factors for early revision. Acta Orthop. 2010 Feb;81(1):66-71.
3. Kuzyk PR. Cross-linked versus conventional polyethylene for total hip replacement: a meta-analysis of randomised controlled trials. J Bone Joint Surg Br. 2011 May;93(5):593-600.
Competing interests: No competing interests