FDA issues MoM hip safety update, proposes PMA application process

Peter R. Kay, FRCS

I think overall, from the U.K. perspective, metal-on-metal has been a real problem. [For] most surgeons in the United Kingdom, our usage of metal-on-metal hip replacements has dwindled to almost nothing because we cannot really find any advantage. The patients do not do any better in terms of function. There is some evidence the patient’s reported pain levels are higher anyway and the revision rate is higher, so it is not adding much value.

In terms of metal-on-metal, we [Medicines and Healthcare products Regulatory Agency] have gone a little bit further than the FDA because we also recommend having a metal ion level test. It is very hard to find a metal ion level where you can say whether patients are likely to run into problems, but one of the reasons we chose to go down that route was that the medical literature is not absolutely clear on whether aseptic lymphocytic vasculitis associated lesion reaction is a hypersensitivity reaction or just a reaction to high metal ion levels. Most patients will have a reaction if the level is quite high. So we chose this level of 7 parts per billion (ppb) for both cobalt and chrome. If you have a level of 7 ppb or above, chances are a fair number of people so far that have problems have levels of that or above that. So, that’s the sort of level where you start to feel more worried. If it’s below 7, what we have discovered is that low levels are rarely associated with a problem, especially levels below 3 ppb.

The difficulty is, the patients who are anxious seem to develop some of the symptoms that are put down as being due to high metal levels. They don’t feel right; maybe their eyes aren’t good; there is a buzzing in their ears. And it is very difficult to reassure that sort of patient. So we have gone a little bit further to suggest that there may be a place for doing a metal ion level test. Not that that metal ion level means you should revise at a particular level, but at a low level we feel we can reassure a patient, and at a higher level we think that can be a sign that things might be going the wrong way.

Lawrence D. Dorr, MD

After review of available data on metal-on-metal articulations with large-diameter heads (LDH) for total hip replacement (THR), the FDA has issued a warning to orthopedic surgeons to be cautious and careful in the use of these implants. The orthopedic community has recognized the increased risk of complications and failure with these articulation surfaces and the use of these implants has plummeted in the past 2 years. It is now recognized this hard-on-hard bearing surface is not forgiving of any impingement or edge loading with the consequence of increased wear and ion levels. The necessity to implant the cup in a narrow range of 15° to 20° anteversion and 35° to 45° inclination puts added pressure on the surgeon to achieve this position. Ian Clarke’s results presented at The Hip Society 2012 Summer Scientific Meeting showed overhang of the large head outside the cup increases the risk of edge loading rather than reducing the risk of impingement.

I have had extensive experience with and published superb results for Metasul THR articulations (Zimmer; Warsaw, Ind.) with 28 mm heads. These results have not been duplicated with LDH metal bearings for the reasons listed, as well as poor engineering and pre-release studies by the companies. At this time, there are better alternatives for the bearing surface for the orthopedic surgeon performing conventional total hip replacement than LDH metal-on-metal.

Reference:

Clarke IC. Paper #44. Presented at: Summer Meeting of the Hip Society; Sept. 13-15, 2012; Rochester, Minn.