Estimating the risk of failure

In 2018 Ian Haley was among a group of 312 patients, who sued Depuy in the English High Court because they had an adverse reaction to metallic debris (ARMD) from the hip’s metallic bearing surfaces. So, they claimed that the Pinnacle Hips with a metal on metal (MoM) bearing were legally defective.

Their claim was based on Part 1 of the Consumer Protect Act implementing the European Product Liability Directive in British Law.

In Article 6 the Directive says:-

A product is defective when it does not provide the safety which a person is entitled to expect, taking all circumstances into account, 

Article 6 (1) of the European Product Liability Directive

The patients’ first claim against Depuy, alleging that the defect was the ‘production of metal wear particles from the bearing surfaces’, is discussed in my previous post.

So now we will turn our attention to the patients’ secondary claim that:-

…”the Pinnacle Ultamet prosthesis had “an abnormal potential for damage, compared with existing established non-MoM total hip replacement prostheses and/or that a large head MoM articulation had an abnormal potential for damage compared to alternative bearing surfaces within the Pinnacle modular system”

Pinnacle Judgement Paragraph 136

The Statistical Evidence

The Judge – Mrs Justice Andrews – established a two stage test for the claimants to satisfy in order to obtain compensation:-

• Firstly, they must show that the risk of revision surgery – to repair or replace their hip – within 10 years was significantly increased by the use of a Pinnacle MoM hip, compared with alternative products already accepted in the market place in 2002.
• Secondly, individual patients must show that, on the balance of probabilities their revision surgery was the result of the increased risk, associated with the development of ARMD

Discussing how the first test could be satisfied, Mrs Justice Andrews observed that:-

How to Prove Products are Defective

The 312 patients, including Ian Haley, seeking compensation from Depuy claimed that their Pinnacle Metal on Metal (MoM) hips were defective, because:-

• Metallic wear particles were shed from bearing surfaces
• Their immune systems reacted to the metallic debris, causing pseudo tumours to develop, damaging their muscle and bone structure – a process described as ARMD (Adverse Reaction to Metallic Debris)
• As a result of ARMD, they required revision surgery to remove and replace their Pinnacle MoM hips, in some cases leaving them with a permanent disability

They did not claim that Depuy had been negligent or failed in their Duty of Care. Instead their claim was made under Part 1 of the Consumer Protect Act (CPA), which implements the European Product Liability Directive in British law.

The Directive says that a producer is strictly – without fault – liable for any harm caused by defects in the products they supply to consumers, and defines a defect by saying:-

1) A product is defective when it does not provide the safety which a person is entitled to expect, taking all circumstances into account, including:-

a) the presentation of the product

b) the use to which it could reasonably be expected that the product would be put

c) the time when the product was put into circulation

2) A product shall not be considered defective for the sole reason that a better product is subsequently put into circulation

Article 6 of 85/374/EEC as amended by Directive 1999/34/EC

If the patients succeeded in proving that:-

• The product was defective
• They suffered the harm
• The defect cause the harm

Then Depuy would be liable for any damage caused by the defect, unless they could use one of the defence arguments permitted by Article 7 of the Directive.

So, the claimants presented two alternative explanations of the defect.

As discussed in my previous post in their primary claim, which was unsuccessful they argued that:-

• The defect was the production of metallic wear particles from the bearing surfaces of the hip joint,
• The harm caused was the need for revision surgery and any resultant disability, pain and discomfort

However, knowing that Depuy might object to that definition of the defect they also presented a second alternative claim, that:-

Legal Argument – What is a Defect?

In 2018 a group of 312 patients including Ian Haley, who had received artificial hips manufactured by Depuy, sued Depuy in the English High Court claiming that:-

• The Pinnacle Hips with a Metal on Metal (MoM) bearings were legally defective, because the patient’s immune system reacted to microscopic wear particles from the bearing surfaces of the joint.
• Typically, their Adverse Reaction to Metallic Debris (ARMD) caused the growth of pseudo tumors in the soft tissue around the joint, and damaged their muscles and bone structure – among other symptoms.
• Patients with severe ARMD required revision surgery to remove and replace their Pinnacle MoM hips. In some cases leaving them with reduced mobility or a permanent disability.

But, the patients did not attempt to prove that Depuy had been negligent, or failed to exercise their Duty of Care

Instead they based their claim against Depuy on the European Product Liability Directive, which has been implemented in British Law by Part 1 of the Consumer Protection Act (CPA).

So in her written judgement the Judge, the Honourable Mrs Justice Andrews analysed the law, explaining how it should be applied – creating a precedent or example that may be used in future.

The Product Liability Directive

The Product Liability Directive was introduced in 1985, because the European Council recognised that the patch work quilt of legislation across Europe needed to be harmonised to:-

• Balance the economic interests of consumers and producers
• Enhance consumer protection

Reading the EU Directive, you will find:-

• The preamble or Recitals, which explain the European Council’s policy objectives and the purpose of the Directive.
• Articles, which define the rules to be implemented in the domestic law of the member states.

Although we may be tempted to fast forward through the Recitals – that is a mistake. The Articles are intended achieve the policy objectives explained in the Recitals – so the Articles must be interpreted in a way that achieves, as far as possible, those policy objectives.

The Patient’s Complaint

Case studies, including this one, help us understand how the Courts have interpreted and applied law, to resolve real world disputes – creating precedents that may be followed in the future.

Depuy developed the Pinnacle metal on metal (MoM) hip, for younger and more active patients needing a ‘robust and durable’ hip replacement, as the result of traumatic injury or osteoarthritis.

Although most of the patients who received the Pinnacle MoM hip were pleased with them, a significant minority – including Ian Haley – developed an Adverse Reaction the Metal Debris (ARMD), as their immune system reacted to metallic wear particles from the hip’s bearing surfaces.

In 2018 a group of 312 patients, including Ian Haley, sued Depuy in the English High Court for compensation, claiming that they were harmed because the Pinnacle MoM hip was ‘legally defective’. So, what can learn from how they presented their case?

The Patient’s Experience

When delivering product liability training we use case studies help develop people’s understanding of the law, showing how it applies in the real world of product design, manufacturing and marketing.

My last post discussed the design and development of Depuy’s range of artificial hips, including the Pinnacle metal on metal (MoM) hip. Introduced to the market in 2000, the Pinnacle MoM hip was designed to be more robust and durable than alternative designs – making it suitable for younger and fitter patients with a more active lifestyle.

Sadly, the Pinnacle MoM hip’s real world performance was worse than predicted in laboratory tests, and it was withdrawn from the market in 2013.

By 2018 Depuy faced 312 claims for compensation from dissatisfied patients in the UK, who had suffered an Adverse Reaction to Metallic Debris (ARMD) – or wear particles – from the hips’s bearing surfaces. Their claims were heard in the High Court under a Group Litigation Order (GLO) by the Honourable Mrs Justice Andrews, and her written judgement reviews the medical history of the six lead claimants- including Mr Ian Haley

The Patients’ Experience

In 2005 when Ian Haley took early retirement from his job as an operations manager, aged 59, he was looking forward to a long and happy retirement on the golf course. He enjoyed playing golf most days, but had some pain and discomfort in his left hip – which got steadily worse. By 2007 the chronic pain in his hip had become unbearable and he was referred an orthopaedic surgeon in Darlington.

Product Liability Case Study

Design and Development of Pinnacle Hips

Depuy, now owned by Johnson and Johnson, developed the Pinnacle range of artificial hips for patients debilitated by osteoarthritis or traumatic injury. The Pinnacle design is a modular system, allowing surgeons to build the hip joint for each patient, using a selection of different bearing materials and components – rather like a medical Meccano kit

Key features of the design included:-

• A CORAIL stem inserted into the the patient’s femur, with cemented and uncemented options
• At the top of the stem, a ball and socket joint with a choice of different bearing materials, including a metallic or ceramic ball (femoral head) with a metallic, ceramic or plastic lined socket (antebellum). Allowing surgeons to select from of the following types of bearing;–.
• Metal on Metal (MoM)
• Metal on Plastic (MoP)
• Metal on Ceramic (MoC)
• Ceramic on Plastic (CoP)
• Ceramic on Ceramic (CoC)
• When using a plastic or ceramic lined socket, the surgeon could select a 28 mm or 32 mm diameter ball, but a larger 36 mm diameter ball was used with the thinner metallic liner – giving a larger bearing area.
• In some circumstances, the modular design also allowed the artificial hip joint to be repaired, rather than replaced, if it was damaged.

The target market for the Pinnacle MoM hips included patients who were unsuitable candidates for other older or weaker designs of hip, due to their age, life style or weight. From a design point of view these more demanding patients presented particular challenges with:-