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Metal on Metal hips and the Consumer Protection Act 1987 (Part Two) - James Bell, Hodge Jones & Allen

27/07/18. The statistical data arguments

The recorded 10-year CRR for the Pinnacle Ultamet Prosthesis in the NJR is 13.98% - which more than double the CRR in the NJR for all external comparators, including the latest and best MoP hips .This was described as the “high water mark of the claimant’s case”.

The 13.98% figure was over three times greater than the 4.18% failure rate for the best MoP hips in the 2017 NJR report.

But the next question was how much reliance could be placed on the figure of 13.98% in the NJR database as a true measure of the risk of revision of the Pinnacle Ultamet?

The court found that the 13.98% revision rate had been skewed due to the 2010/2011 “toxic hip” media panic. This hysterical media coverage was identified by the court as having had a very substantial effect on the revision rate of the Pinnacle hip.

The court found that “media reports of possible adverse consequences from MoM protheses had the potential to cause a so-called “nocebo” effect in some patients, whereby the expectation of symptoms becomes self-fulfilling. This could manifest itself in heightened anxiety, causing patients to monitor themselves more closely, and in patients noticing and remembering symptoms that they might otherwise have missed or disregarded. It could also lead to a subjective perception of increased pain and/or a loss of function; a misattribution of pain; and/or an increased willingness on the part of some patients to seek help, or to consent to revision surgery.”

Even worse, there was a ‘nocebo’ effect on the surgeons also – who were often quick to revise hips in 2010/2011 due to the fear of what damage could be caused by cobalt-chrome debris in an unrevised MoM hip. Accordingly, if a patient developed somatic pain as a result of reading the adverse media coverage, and reported it to their surgeon, it might well be enough to convince the surgeon, particularly an ultra-cautious one, to perform a revision.

Ironically, the design of the Pinnacle modular system which made it relatively straightforward to swap the head and/or liner also had a part to play in this.

Also four “outlier” surgeons were identified as being surgeons who had been very cautious indeed with their patients and had revised their patients Pinnacle hip patients at an early stage on a very frequent basis. The “surgeon outlier” effect alone would suggest that the Pinnacle had a CRR of somewhere between 10% and 11% rather than 13.98% as alleged.

Additionally the Pinnacle hips were designed for younger, active patients (i.e allowing for a good range of movement). The NJR also contains data for hip devices designed for and implanted into older, more sedentary patients that will almost certainly remain in situ for the patient’s entire lifetime.

The relevance of the 10% failure rate is that National Institute for Health and Care Excellence (NICE) guidance in April 2000 stated:

Using the most recent available evidence of clinical effectiveness, the best prostheses (using long term viability as the determinant) demonstrate a revision rate (the rate at which they need to be replaced) of 10% or less at 10 years. This should be regarded as the current “benchmark” in the selection of prostheses for primary Total Hip Replacement”.

But note that this was a benchmark for NHS surgeons– not a line upon which a product either should be labelled either as “defective” or “not defective”.

The figure of a CRR of 10% at 10 years took no account of the higher failure rates for implants in younger and more active patients.

The judge found that it “did not follow that a hip prosthesis that turned out to have a higher failure rate at 10 years than the target set by NICE fell below the entitled expectation of safety, even if the aim for the future was that clinicians working in the NHS would select for use the best prostheses….”

The judge ruled that if a product had a failure rate of 12% or 13% at 10 years that would not necessarily make it “defective” as defined by the CPA 1987. But the court suggested that “…if hip product A failed at 50% within 10 years because of some common characteristic that caused them to fail, and at least 90% of all other types of prosthesis that were available at the time that product A came on the market would last for 10 years or more, one could more easily reach the view that prosthesis A not only failed to meet performance expectations but also fell below the standard of safety that the public generally was entitled to expect.”

The engineering case

Finally, it was alleged by the claimants that there were design defects with the Pinnacle product. This was dealt with very briefly in the judgement. The judge found that “the Pinnacle system, taken from the evidence as a whole...was a well-designed product with many positive engineering features”.

At the start of the trial, the claimants relied upon expert engineering evidence that criticised various design features of components used within the Pinnacle system. Some of these criticisms turned out to have been based on a mistaken factual premise and were withdrawn. Those that remained were dismissed. The claimant’s engineering expert, Professor Gill was found to have given evidence, which “…when taken at face value, was seriously misleading.” The judge also commented that he did not have “any confidence in him as a reliable independent expert”.

The lead claimants

The medical records of six lead claimants were reviewed as part of the trial. These were patients who had their Pinnacle hips revised. Their case were analysed in close detail and four of the six were found to actually have not suffered ARMD, their hips having being revised based on an abundance of caution. This probably indicated to the judge the unreliability of using NJR data on wider scale.

What lessons can be learnt from this litigation?

It is not enough to assert that the harm produced by a product is in fact the defect complained of. The judgement ruled that the claimant’s argument (the propensity to cause ARMD being the defect) taken to its logical conclusion essentially meant that all MoM prostheses would be deemed defective, irrespective of design or the amount of metal debris they produced. Further, no manufacturer would be able to avail themselves of the development risk defence because the risk of metal debris was a known one.

A product has to be very much worse than comparator products before it can be defined as defective. A few percentage points worse over a period of 10 years is not enough.

This case has also shown the limitations of using national hip registers to win a legal case. Simply relying on bald CRR data alone cannot of itself prove that a hip prosthetic is defective unless the failure rate is much much higher than similar products.

The Pinnacle hip simply cannot be said to be defective product on the evidence available. It is not performing as well as a new hip prosthesis available in 2017 but of course hindsight cannot be part of the assessment of safety under the CPA 1987. As of 2002, when it was released to the market, the Pinnacle was performing broadly in line with the standards of the time. The product was judged on the standards applicable upon its release in 2002 – not the standards of 2013 when it was withdrawn from sale.

Also, it was simply not a provably bad product according the NJR and SHAR data collated over its market lifespan in the years 2002 – 2013. The NICE benchmark of a 10% risk of CRR over 10 years is nothing more than that - a benchmark. The NJR is not meant to be used a legal measure of defectiveness for the purposes of CPA 1987.

I would suggest that in order to win a defective hip or knee prosthetic case the claimant must to be able to prove that the device is very demonstrably poor according to NJR or SHAR data. Also, even in such cases, a suitable allowance must made for a large portion of the data to be deemed to be corrupt by the trial judge.

In future cases, the claimants will also need to show, with robust engineering evidence, that there is an identifiable design or manufacturing defect that has caused the harm alleged. Identifying the harm that has been caused as the defect complained of is not sufficient.

Ide v ATB Sales Ltd [2008] EWCA Civ 424 makes clear that this evidence of failure does not have to be beyond reasonable doubt clear cut evidence of negligent manufacturing. But there must be a good explanation of the mechanism of failure that is readily understandable and logical, backed up with good expert evidence with all other possibilities of non-defective failure excluded.

James Bell is a partner in the medical negligence team at Hodge Jones & Allen Solicitors.


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