In a study published this week in the British Medical Journal, researchers have used statistical techniques to analyse data from almost 300,000 patients implanted with prosthetic hips, looking specifically for evidence of increased cancer risk in the metal-on-metal population. The Linkage study compares implant patients with a matched population extracted from Hospital Episode Statistics. The study suggests there is no increased risk of cancer in metal-on-metal patients compared with other bearing types and a slight reduction compared with a matched population.
In view of the claims being bandied about regarding the association between metal-on-metal hip prostheses and risk of diseases including cancer, this study was undertaken in order to interrogate the extensive data collected in the National Joint Registry for England and Wales and determine whether any link exists.
Specifically the analysis looked at whether metal-on-metal bearing surfaces are associated with an increased risk of a diagnosis of cancer in the early years after total hip replacement and specifically with an increase in malignant melanoma and haematological, prostate, and renal tract cancers.
The paper can be found here.
The data set comprised 40,576 patients with hip replacement with metal-on-metal bearing surfaces and 248,995 with alternative bearings.
Main outcome measures included Incidence of all cancers and incidence of malignant melanoma and prostate, renal tract, and haematological cancers.
For reasons that are not altogether easy to explain, the incidence of new diagnoses of cancer was lower after hip replacement than in an age and sex-matched normal population. This has also been found in another study cited in the paper.
Compared with alternative bearings, there was no evidence that metal-on-metal bearing surfaces were associated with an increased risk of any cancer diagnosis in the seven years after surgery.
While the authors agree that their analysis is reassuring, they also admit to the study’s limitations, not least its reliance on official Hospital Episode Statistics for a representative age and sex-matched population. When comparing bearing surface types, they admit that the study is limited by its duration, with the possibility that cancers with longer latency periods may not have been captured. Also the findings are observational rather than randomised and controlled. The abstract closes by stating that “it is important that we study the longer term outcomes and continue to investigate the effects of exposure to orthopaedic metals”.
This study may be completely meaningless or highly valuable or somewhere in between. It’s difficult to know, but it does seem to add to the knowledge base somewhat at least in helping to define what the real data requirements might be.
Source: British Medical Journal, (BMJ 2012; 344 doi: 10.1136/bmj.e2383 (Published 3 April 2012)