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

25/06/18. Metal on Metal hips (MoMs) were introduced by the four leading orthopaedic prosthetic companies to the hip prosthetic market on a wide scale in the early 2000s.

Stryker, DePuy, Zimmer and Smith and Nephew all produced very similar MoM models as the industry moved to using all metal products after earlier attempts had tried and failed in the 1980s.

The distinguishing feature of these second generation MoM hips was that both the ball and socket of the hip prosthesis were to be made of an alloyed metal, namely cobalt–chrome.

They were marketed to surgeons as an improvement on the Metal on Polythene (MoP) ball and socket joints which had dominated the market during the 1990s.

Interestingly, the “problem” which MoMs sought to fix was the propensity of a MoP ball and socket to shed plastic and metal debris through normal wear on the moving parts. This could then lead to the destruction of the surrounding bone - a process called osteolysis. It was therefore reasonably thought that products utilising harder materials such as cobalt-chrome would reduce the incidence of wear and the need for revision due to excessive debris.

In 2002 a UK database (the National Joint Registry or NJR) of all implanted hips was created. The purpose of the database was to monitor the safety of prosthetic hips after they had been approved for use. The NJR was set up following a recommendation of a Royal College of Surgeons report into the high-profile failure of the 3M Capital Hip. This hip featured a plastic ball and socket joint with a metal stem.

Stem loosening led to 40% of 3M Capital hips failing within five years of implantation. This device failure alone led to the creation of the NJR whose intention was to monitor the early failures of hip and knee devices and attempt to identify similar problems at an early stage – to prevent another 3M situation.

For medico legal purposes a hip is deemed to have “failed” if the patient undergoes...

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