Metal on Metal Hip Replacement
Summary of Emerging Concerns

Introduction

The purpose of this page is to summarize the general concerns about metal on metal hip replacement.

These concerns are widely acknowledged with a lot of information published in the public domain in recent years on the higher than expected revision rates, for example at around the five year point, and numerous product recalls for metal on metal implant systems.

At the foot of the page I have provided links to some of the safety alerts and communications issued by the international regulatory agencies.

Metal on Metal Hip Replacement - Summary of the Main Concerns

There are risks associated with all artificial hip implants, including the risk of particle release due to friction as the components move and rub against each other. Metal on metal hip the implants carry some unique and specific risks in addition to the general risks associated with all artificial hip implants.

Specifically, with metal on metal hip replacement systems, the hip articulation involves two or more metal surfaces moving against each other as the patient moves, for example during walking, running, cycling or swimming. Typically, a metal ball at the top of the femur sits inside and slides against an acetabular metal cup.

Through time, as the component wears, very small metal particles and / or metal ions (chromium and cobalt) may be released into the hip area around the implant, and some of these metal particles may enter the bloodstream and thereafter circulate around the body.

Orthopaedic surgeons take great care when they plan and carry out metal on metal hip replacement surgery to try to minimize the potential for the metal components to wear.

For example, the correct sizing and relative positioning of the components can influence the way the ball and socket rub against each other. The extent to which this optimization can be achieved, among other factors such as patient activity levels and body weight, will influence the rate of wear and the level of metal particles released. Nevertheless, the release of some metal particles seems to be unavoidable.

Different people seem to react in different ways to these metal particles. There are many variables involved for any one patient and it is not possible to predict:

  • Whether a patient will experience a reaction
  • The type of reaction that might be experienced
  • When a reaction might occur (if it does),
  • The severity of the reaction

It is thought possible that at any given level of exposure to metal particles, some patients may experience a reaction whereas others may not.

The potential adverse effects of the release of metal particles from metal on metal hip replacement systems fall in to two broad categories:

A) Local - Adverse Local Tissue Reaction (ALTR) or Adverse Reaction to Metal Debris (ARMD) - essentially damage to the tissue and / or bone surrounding the implant. This may lead to pain, component loosening, joint failure and the potential need for revision surgery.

B) Systemic - A range of adverse effects caused by metal particles entering the blood. There is emerging evidence that suggests that some patients with metal on metal hip implants may have experienced adverse reactions to metal particles released by the implants, and that a range of medical problems might therefore be related to their metal on metal implants (see note 1 below) These problems include:

  • Neurological problems including sensory changes: visual impairment; auditory impairment
  • Skin rashes (hypersensitivity reaction)
  • Change in psychological status, including possibly cognitive impairment or depression
  • Thyroid problems which might result in: weight gain, tiredness, neck pain, feeling cold
  • Cardiomyopathy - heart muscle disease potentially resulting in a measurable deterioration in the performance of the heart muscle
  • Impairment of the renal (kidney) function

Note 1 : It is important to note that (as at Sept 2012) the evidence collected globally does not yet establish a definitive link between the use of metal-on-metal implants and the symptoms listed immediately above, but research is ongoing to establish whether there is a definitive (proven cause and effect) link.

Useful links

Regulatory bodies in various countries have issued communications and safety alerts related to metal on metal hip replacement. Links to a sample of these communications are provided below.

Please note : this is not a complete list of links covering all countries: you should do your own research to find the communications and safety alerts that apply to the country where you live.

Also, alerts such as those linked below are updated from time to time, so you should always check that you referring to the most recent information published by the appropriate regulatory body.


Australia : The Therapeutic Goods Administration of Australia - safety information on metal on metal hip replacement (September 2012)

Canada : Health Canada - Public Health Communication regarding metal on metal hip implants (May 2012)

United Kingdom : The Medicines & Healthcare products Regulatory Agency (MHRA) - medical device alert (June 2012)

USA : FDA Safety Communication: Metal on Metal hip implants (January 2013)