BMJ’s reply to DePuy’s criticisms of article on safety of metal-on-metal hip implants

The response from DePuy representatives Graham Isaac and Simon Sinclair sidesteps the substantive concerns described in the BMJ feature on the safety of metal-on-metal hip implants.1 2 3

The main thrust of the article was the laxity of medical device regulation: a whole class of implant—in this case large diameter metal-on-metal total hip replacement—was allowed to enter the global market without any clinical studies to assess their safety and effectiveness.

The authors acknowledge that “constituents of cobalt and chromium would be released locally and systemically” after the devices were implanted.1 It is concerning that the manufacturers did not try to establish through clinical studies what levels would be considered safe for patients before rushing to market or modifying the design of the implants.

They say that the BMJ failed to quote the proper figures from the literature about metal ion levels.1 2 The article clearly described the range of 5-20% from the three referenced studies. The conclusion of one of these cited papers said that the authors “no longer recommended the use” of such metal hips.4

Our focus was not on cancer. We said that there was no evidence of a link, but highlighted how little was known about the long term effects of the metal ions.

As Isaac and Sinclair point out, Japanese surgeons identified problems with one of the stems used with the Pinnacle, but it took DePuy over two years to advise doctors in Japan not to use them.

The fact that these stems were 9/10 rather than 12/14 in the context of this article is irrelevant to the point being made.1 2 Concerns from the Japanese surgeons were included because they discussed the same patterns of failure as those being reported from Virginia in the US and North Tees in the UK since 2010.

Isaac and Sinclair say that the BMJ was wrong to claim that the design changes to the stem dated from around 2004. The Food and Drug Administration says that the Corail stem—the one most commonly used in the Pinnacle hip system—was cleared for use in 2004. That we cannot say precisely when these design changes were introduced into clinical practice is an indictment of the lack of transparency surrounding device regulation and the fact that individual components of a hip system can be cleared separately with no clinical testing.