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SICOT e-Newsletter

Issue No. 46 - July 2012

Worldwide News

Failure rates of stemmed metal-on-metal hip replacements: analysis of data from the National Joint Registry of England and Wales
Alison J Smith, Paul Dieppe, Kelly Vernon, Martyn Porter, Ashley W Blom; on behalf of the National Joint Registry of England and Wales, Lancet 2012; Mar 12 [Epub ahead of print]

Comment by Aad Dhollander

Summary:

Background
Total hip replacement (THR) is extremely common. Some prostheses fail, particularly in younger patients, and need to be revised, most commonly for loosening secondary to wear or dislocation. Surgeons have tried to address these problems by implanting large diameter metal-on-metal bearing surfaces. Our aim was to assess if metal-on-metal bearing surfaces lead to increased implant survival compared with other bearing surfaces in stemmed THR and, additionally, if larger head sizes result in improved implant survival.

Methods
We analysed the National Joint Registry of England and Wales for primary hip replacements (402051, of which 31171 were stemmed metal-on-metal) undertaken between 2003 and 2011. Our analysis was with a multivariable flexible parametric survival model to estimate the covariate-adjusted cumulative incidence of revision adjusting for the competing risk of death.

Findings
Metal-on-metal THR failed at high rates. Failure was related to head size, with larger heads failing earlier (3•2% cumulative incidence of revision [95% CI 2•5–4•1] for 28 mm and 5•1% [4•2–6•2] for 52 mm head at 5 years in men aged 60 years). 5 year revision rates in younger women were 6•1% (5•2–7•2) for 46 mm metal-on-metal compared with 1•6% (1•3–2•1) for 28 mm metal-on-polyethylene. By contrast, for ceramic-on-ceramic articulations larger head sizes were associated with improved survival (5 year revision rate of 3•3% [2•6–4•1] with 28 mm and 2•0% [1•5–2•7] with 40 mm for men aged 60 years).

Interpretation
Metal-on-metal stemmed articulations give poor implant survival compared with other options and should not be implanted. All patients with these bearings should be carefully monitored, particularly young women implanted with large diameter heads. Since large diameter ceramic-on-ceramic bearings seem to do well we support their continued use.

 

Comment:

Recently, controversy has arised about the use of metal-on-metal hip replacements. In February 2011, the U.S. Food and Drug Administration (FDA) issued a public health communication about hip replacement components that have both a metal ball and a metal socket (metal-on-metal hip devices). In this article data from the National Joint Registry of England and Wales - established in 2003 and the largest arthroplasty database in the world - were used to assess if metal-on-metal bearing surfaces lead to increased implant survival compared with other bearing surfaces in stemmed THRs.

This article was published in a very high-impact journal, 'The Lancet'. The conclusions were based on a large amount of data (31171 metal-on-metal hip protheses). The statistical analysis, results and conclusions were clearly presented.

However, the presented data were based on stemmed metal-on-metal THR’s only, no resurfacings were included. Furthermore, ASR implants were excluded from the metal-on-metal analysis. These two facts are very important in the metal-on-metal discussion and in this way the general perception created in this study should somehow be relativized. Moreover, the data were retrieved from one national joint registry only. One could question if the results of one registry are enough to draw any broad conclusions.