We Don't Know What We Don't Know: Hip Replacement Edition

A striking result from The Lancet has led researchers in Britain to urge banning metal-on-metal hip replacements in that country:

Data on more than 400,000 hip replacements found metal-on-metal implants needed revising more often than other types and that failure rates were higher in women.

It comes two weeks after the Medicines and Healthcare products Regulatory Agency (MHRA) issued new guidance on the implants, saying almost 50,000 patients in the UK will need annual blood or MRI checks.

That’s bad, of course, but the danger is mitigated in the U.K. by the fact that only about a tenth of hip replacements in that country are metal-on-metal—and it’s been decreasing, also. The process would seem to have worked—you’ve got data from a large registry; the data is worrying; you act upon it.

Contrast, of course, to the U.S. The study cites the rate of U.S. metal-on-metal hip replacements at 35%...in 2009. It appears the study has no more recent source of data, and I wasn’t able to find anything more recent in my own searches. That’s because we have no such registry and therefore aren’t able to track the failure rates of hip replacements in the field. As ever, we don’t know what we don’t know.