After reviewing the latest research, the British Hip Society has advised a ban on all large diameter metal-on-metal primary total hip replacements. This announcement comes only days after the Medicines and Healthcare Regulatory Agency (MHRA) released its’ updated guidelines for patients with metal-on-metal hip implants. Metal hips have been a controversial healthcare topic for the past few years, particularly after DePuy Orthopedics massive recall in 2010 of its ASR Acetabular Hip Replacement System and ASR Hip Resurfacing System.
For some time, metal-on-metal hip implants have been linked to increased levels of metal ions in the blood, which are potentially carcinogenic. Reportedly, the friction between the metal components causes debris, releasing chromium and cobalt ions into local tissues that subsequently undergo necrosis. According to studies cited by the New York Times, large diameter heads, meaning those that are 36 millimeters or greater, are of particular concern because the interaction between the enlarged head (femoral component) and socket (acetabular component) only further facilitates the release of harmful metallic debris.
Last year at the British Hip Society Annual Conference, large diameter metal hip replacements were a main concern. The British Orthopedic Association had released a statement discussing the high failure rate of the implant; data indicated that the rate of revision, in which patients needed additional surgery, could be as high as 49 percent after 6 years. Findings also suggested a higher failure rate in women. According to the statement, the failure is mostly attributed to loosening of the head or socket, or to a metal reaction that caused tissue damage. There was also concern over whether the trunnion, the part of the stem that connects to the head, was causing problems. In 2004, manufacturers had shortened the trunnions as part of a design tweak; because of a regulatory loophole, the modification was approved without any clinical studies, according to a BMJ article published last week.
Now, the British Hip Society’s latest announcement only confirms earlier suspicions. At last year’s conference, the association had said that “the use of large diameter metal on metal bearings in primary total hip replacement should be carefully considered and possibly avoided.” Now, the use of these implants is being stopped altogether in the UK. The most recent statement said that, “Large diameter metal-on-metal primary total hip replacements using bearings of 36 mm or above should no longer be performed until more evidence is available, except in properly conducted and ethically approved research studies”. They have not, however, released any updated guidelines concerning hip resurfacing, one of the products recalled by DePuy two years ago. The statement advocates the continuation of the latest MHRA guidelines, which recommend that those with large diameter head replacements undergo monitoring for the life of the implant. This recommendation was applied for all types of DePuy ASR hip replacements. Those with smaller replacements are advised to follow-up for at least five years. Professor Joe Dias told The Telegraph, “It is clear that as a class these large metal on metal implants, which were introduced to make the implant last longer in younger patients, are not fulfilling that aspiration. Because they are not fulfilling that aspiration, in that at the moment they are worse than metal on plastic, it does not make sense that surgeons continue to use them.”