Tuesday 1 January 2013

What's the deal with those bad hip replacements?

Most people are aware that a year or two ago there were some new hip replacements that were recalled. The story behind it has all the ingredients to suit this blog: overestimation of benefit, underestimation of harm, regulation failure, and conflict of interest up the wazoo. The ‘deal’ as it were, was a bad one for patients, a bad one for the company (in the end), but a great one for the surgeons, as it became the gift that keeps giving.

Hip replacements have been around for about 50 years and millions have been implanted. Widespread uptake began after pioneering work by Sir John Charnley. After testing several techniques and materials, he settled on “metal on poly” – a metal ball and stem that articulates with a plastic (high density polyethylene – “poly”) cup. Although there have been modifications along the way, metal-on-poly is still the gold standard today and by far the commonest type of hip replacement used. It is the only type I use.

In 2005, the device manufacturer De Puy introduced the ASR metal-on-metal (MoM) hip replacement.

MoM hips actually pre-date metal-on-poly, but the originals from the 1950’s were a failure. Refinement in engineering saw MoM hips relaunched in the 1990’s, and the ASR was a “me-too” implant aimed at securing market share for the demand. The idea is that MoM will last longer, because the poly in metal-on-poly hips eventually wears out (although only by millimetres over decades, and newer “highly cross-linked” poly wears even less). Without any long term results or head-to-head tests, they were approved and introduced. They were mainly used in younger patients. There was no objection from the FDA, who basically rubber stamped it.

Yet there has never been good evidence supporting MoM hips over standard metal-on-poly hips (here).

The problem with MoM hips was the problem with so many other things in medicine: it sounded good, but was never properly tested. I have covered the reasons why surgeons do things that are not properly supported in a previous blog post here. All you need is the ‘wobbly tripod’ of evidence: 1. biological plausibility (metal is harder than plastic, so it will not wear out as fast), 2. some non-clinical results (it was harder, so it didn’t wear out as fast in the lab), and 3. personal experience (it seemed to work, at least in the short term).

And so MoM hips were used widely in many countries – on hundreds of thousands of patients. What happened? Well, they didn’t wear out; there wasn’t time for them to wear out because of all the other things that went wrong with them first. What happened is what often happens with something that sounds good on a superficial level: unintended consequences.

Even the little friction that was present in the design was enough to release metal ions in to the body. Unusual reactions to the metal led to pain and loosening from a type of immune response. There were also reports of systemic complications. There have been other problems reported from MoM implants. A good summary of the problems with MoM hips and some timelines are provided in this BMJ article.

The failure rate was reported as unacceptably high in some joint replacement registries, like the Australian National Joint Replacement Registry, from as early as 2007. It was withdrawn from the market in Australia by the regulators in 2009 because of the consistently high failure rate.

But it continued to be used in the USA. The company eventually recalled the implant until August 2010. In the meantime, they were paying “thought leaders” millions of dollars. Not surprisingly, these thought leaders were protesting that the ASR was fine and were denying the existence of any problems with the device; we just weren’t using it properly. One surgeon in particular penned articles supporting the MoM hips, and defended their use at meetings, where the audience were not always aware that he had received 3 million dollars from De Puy.

Who is the bad guy?
Everyone likes to blame device manufacturers for putting something on the market without evidence of superiority or long term evidence of, well, anything. But hey, they are just trying to make a buck and responding to surgeon demand. The regulators should have stopped them – there should be checks in place to stop this kind of thing, right? Well yes, but why is nobody blaming the surgeons for using these implants in the first place?

Surgeons are always keen to use something new, particularly if there appears to be a technological edge. Such new, expensive and (literally) shiny devices are appealing to to surgeons; they are assumed to be better. There are secondary gains: the surgeon can appear to be at the cutting edge, get an advantage over competitors, and might even be able to charge more.

The bottom line
De Puy lost out, and they are still paying millions in lawsuits. The regulators got through unscathed, and according to their own recollection of events, they are the hero (here).  The surgeons who put them in, however, are now being paid top dollar by De Puy to take them out again (click here and then click on “treatment” tab). So the surgeons who used these unproven devices in the first place have been rewarded with more surgery at the top rate, and none have been penalised. That’s why MoM is the gift that keeps giving.

Other links:
The most detailed review of the ASR recall is this BMJ article. An overview of the problems can be seen on the DrugWatch website, the Failed Implant Device Alliance site and on Wikipedia. This New York Times article looks at the costs of failed MoM hips (not just from De Puy).


  1. In medicine we are obsessed with being "up to date" Yet we confuse new with better. New treatments or devices are presented as breakthroughs but are often just another product. So playing to doctors desire to be "up to date" is highly effective marketing.

    1. Couldn't have put it better myself. This phenomenon is clearly demonstrated in joint replacement surgery where I have seen so many new, more expensive variations introduced over the years, only to see them come off the market soon after introduction.

  2. You failed to mention the legal concept of the Learned Intermediary. Medical Device Companies have no obligation to warn patients of the risks or benefits of any device such as MOM's they are only required to warn/inform our learned intermediary doctors who must then warn/inform patients. Letting surgeons off the hook on MOM's is completely unethical. Unfortunately an uninformed learned intermediary is no better than a learned idiot.

    1. Thanks, but while I did not specifically mention the term "Learned Intermediary", I certainly didn't let the surgeons off the hook. In fact, the whole point of the post was that surgeons are never blamed for things like this, only the companies and the regulators. The ASR problem would not have existed if there was no surgeon demand for the product.

      I think we are in agreement, however, that our intermediaries could be a little more 'learned'.

  3. Great post as usual. I love to see a surgeon think critically about surgery!!

  4. Hi Michael,

    I loved reading this piece! Well written!

    Merlen Hogg
    Dr Skeptic


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