Study on metal-on-metal hip implants was halted a year before UK regulator banned their use

An unpublished trial of a metal-on-metal total hip replacement, funded by the US medical device company Stryker, was stopped early more than a year before the UK regulator told surgeons not to use the implant, the BMJ has learnt.

Earlier this month the Medicines and Healthcare Products Regulatory Agency (MHRA) told surgeons to stop using the MITCH TRH cup/heads, made by Finsbury Orthopaedics (now Depuy), in combination with Accolade femoral stems made by Stryker Orthopaedics.

The instruction came after the National Joint Registry for England and Wales showed a higher than acceptable revision rate of 10.7% at four years among 271 patients.

However, a Stryker funded trial conducted at the Freeman Hospital in Newcastle upon Tyne was stopped more than a year earlier after it showed that the hip prosthesis was failing two years after being implanted.

The trial recruited 73 participants from December 2007, 37 of whom were implanted with a metal-on-polyethylene total hip replacement and 36 with the metal-on-metal MITCH TRH total hip prosthesis.

The trial’s chief investigator, Nigel Brewster, an orthopaedic surgeon at the Freeman, told the BMJ that within two to three years 9% of patients in the MITCH TRH arm needed to have their hip revised. He scanned them after they came back to him with pain and found that tissue around the joint was inflamed and necrotic.

“The increased reaction to metal debris in these patients was completely unexpected and led me to discontinue the trial,” he said. He is currently following up the patients and publishing the results.

The BMJ asked Stryker whether it had conducted any studies on the implant, but the company declined to say and said it was the responsibility of Depuy (which bought Finsbury Orthopaedics in 2009) to oversee the safety of the implant—even though Stryker had been marketing it across Europe.

Both the MHRA and Stryker declined to tell the BMJ the reasons for the failure of the hip implant. Depuy told the BMJ that it was investigating.

The trial adds to the list of studies that have picked up problems with some types of metal-on-metal hip prostheses. It also challenges the MHRA’s stance that pre-market clinical trials would not pick up problems before hip implants are put on to the market.

“Long term performance of implants cannot be adequately studied in pre-market studies of feasible size,” the MHRA’s chief executive, Kent Woods, said in a letter to the BMJ last month (www.bmj.com/content/344/bmj.e1410/rr/573500).

Neither Depuy nor Stryker responded when the BMJ asked whether either had conducted any clinical studies on the MITCH TRH cup/head combined with the Accolade stem.

Art Sedrakyan, director of the comparative effectiveness programme at Weill Cornell Medical College in New York, said that a two to three year clinical study comparing the implant with a good control—namely, the best performing comparable implant—can highlight poorly performing devices before they enter the market but that companies are reluctant to conduct such studies because of the costs.

Rising concern about the safety of metal-on-metal hip implants led the MHRA in February to issue updated guidance on the lifelong follow-up of patients with large diameter implants, which indicated that a blood metal ion concentration of over seven parts per billion was a cause for concern because of the potential for soft tissue reaction (BMJ 2012;344:e1545, 29 Feb, doi:10.1136/bmj.e1545). However, Brewster’s trial found that patients who had reactions to the metal debris had metal ion concentrations under this threshold.

The MHRA guidance in February was prompted by a joint BMJ and BBC Newsnight investigation highlighting design changes that are thought to have led to a high failure rate in large diameter metal-on-metal total hip replacements (BMJ 2012;344:e1410, doi:10.1136/bmj.e1410).