This article originally appeared in Issue 4 (March 2020).
Modern medicine increasingly makes use of sophisticated technology, from algorithms for assisting in diagnosis to robots for surgical procedures. But what happens when the technology goes wrong; who is liable and what standard are patients entitled to expect from medical devices? The Outer House of the Scottish Court of Session grappled with these questions in a significant judgment handed down on 26 November 2019.
A former forestry worker brought a claim against the manufacturers of a metal-on-metal total hip replacement (“MoM THR”) prosthesis. The device consisted of a Mitch/Stryker Howmedica uncemented acetabular cup, manufactured by the First Defendant (actually ‘defender’, as this was a Scottish case), and an Accolade V40 uncemented femoral stem, manufactured by the Second Defendant. As of April 2012, when a ‘field safety notice’ (effectively a recall notice) was issued regarding this particular prosthesis, it has no longer been used.
The Claimant (or ‘pursuer’) had a history of arthritis and on 4 March 2009, aged 54, underwent a left hip replacement using the MoM THR device. He then underwent the same procedure on his right hip a few months later, on 16 November 2009.
There was no suggestion that the hip replacement surgery was carried out negligently, nor that the particular prostheses themselves were made in a negligent or faulty manner. However, the MoM THR shed metal debris which meant the Claimant suffered an adverse reaction and had to have revision surgery on his left hip some three years later.
The claim was brought under the provisions of the Consumer Protection Act 1987, section 2 of which imposes no-fault liability on a manufacturer for damage caused wholly or partly by a defect in a product. Section 3 defines a product as defective if its safety is not such as persons generally are entitled to expect. The claim therefore proceeded to a preliminary issue hearing to resolve the question of whether certain propensities and risks inherent in the MoM THR prostheses meant that they were defective within the meaning of s.3 of the 1987 Act.
Very detailed evidence was provided by six factual witnesses from the Defendants about the development and manufacturing process of the MoM THR prostheses, and then from eight experts (four apiece for the Claimant and Defendants) in orthopaedic surgery, biomechanics, immunology/toxicology and histopathology. This is set out at length in the judgment, which also borrows heavily from the earlier case of Gee and others v Depuy International Ltd  EWHC 1208, in which Andrews J found in favour of the Defendant manufacturer in a similar challenge to a different type of hip prosthesis system.
It was accepted by the manufacturers that there was an inherent propensity of MoM THR devices of this type to shed metal debris and a risk that some patients may suffer an adverse reaction. The question for the court was whether this was significant enough to make the devices defective as at the date of supply, taking into account the knowledge of orthopaedic surgeons at the time, the information available, and any advice and warnings issued by the manufacturers, suppliers and regulatory authorities.
Lord Tyre held that they were not defective, applying a two-stage approach.
First, he considered what the “entitled expectation of safety was”. He emphasised that the level of safety which patients were entitled to expect, for the purposes of s.3 of the 1987 Act, is a legal concept not a medical term of art . Surgeons are more familiar with discussing ‘clinical efficacy’ or ‘known side-effects and risks’ rather than ‘safety’, but those are not the same. What the entitled expectation of safety meant was that (subject to de minimis considerations) the level of safety of MoM THR devices in 2009 was not worse than existing non-metal-on-metal products that could otherwise have been used.
Second, he considered whether the product failed to meet the entitled expectation of safety. The answer to this was ‘no’. Despite the fact that the Claimant’s experts were preferred on several matters, such that the Claimant had proved there might be a causal link between the shedding of metal debris and injury, this was only in a small number of cases and not necessarily for reasons specific to MoM THRs. The judge noted that the combination of a metal stem and metal cup had been used in other implants and prostheses without any significant damage. The particular combination of cup and stem which the Claimant received was only on the market for a short time, but the data did not suggest it had a materially lower survival rate than other available products. Overall, when he considered the revision rate for MoM THRs and the prospects of success of revision surgery compared with other prostheses, which were the two most important ‘safety’ criteria, he was not persuaded that these were worse for MoM THRs at the relevant time.
However, Lord Tyre did expressly leave the possibility open that another Claimant might be able to present evidence in relation to a different product or product combination which demonstrated a defect, so this judgment is not the end of the story for MoM THRs as an entire class of device.
This judgment contains a clear summary of the law on Consumer Protection Act claims as they relate to medical products. It also illustrates how detailed and complex the evidence in such a claim can be, particularly the expert evidence. Finally, it provides a stark example of how critical the state of knowledge and information about a product at the relevant time is for product liability cases. It is not enough to show that there are now concerns about a device or product; the key question is what the state of knowledge was (or should have been) at the time it is used, and this can be a difficult question to answer.