FDA panelists last week agreed that, although there are no circumstances in which metal-on-metal hip implants are better than the alternatives, the medical devices should be left in patients who aren’t experiencing any problems.
A number of recent publications, studies and registry reports have raised safety concerns for MoM total hip replacements, garnering wide media attention and public outcry. More than 750,000 people in the U.S. have the cobalt-chromium implants, panelists noted during the meeting June 27-28. The implants became the target of intense criticism after Johnson & Johnson (NYSE:JNJ) recalled hip systems made by its DePuy Orthopedics subsidiary over concerns that a higher-than-normal number of patients required surgeries to correct or remove defective implants.
The U.K.’s Medicines and Healthcare products Regulatory Agency published a Medical Device Alert last February, detailing the management and monitoring of patients implanted with MoM hip systems and recommending more aggressive follow-up of patients with larger total hip replacement systems (≥36mm).
While the data suggest that a large percentage of patients with MoM hip systems have successful outcomes, an article in The Lancet raised serious concerns about the failure rates of MoM hip systems in Great Britain. There was an increased failure rate after 5 years for MoM total hip replacements, related to larger head sizes and significantly higher risk for revision surgery in female patients. Revision rates for dislocation in men with MoM replacements were slightly lower, showing some benefit to larger head sizes, according to the article. An Australian registry reported higher revision rates for patients with large-diameter head implants (>28 mm).
The panel’s recommendations
Panelists on the Center for Devices & Radiological Health’s orthopedic devices advisory committee said most patients with MoM implants will not experience any problems shouldn’t fear that their device is a "ticking time bomb," but should be aware that problems associated with the devices have been reported, including local complications such as pseudotumors and aseptic lymphocytic vasculitis-associated lesions, early device failure and the need for revision surgery, and systemic complications from metal ion exposure. Patients should be monitored routinely post-operatively by the surgeons who placed the device, panelists advised.
The FDA asked the panel to discuss how the devices fail, metal ion testing, imaging methods, local and systemic complications, pre-operative and post-operative risk factors and clinical follow-up considerations.
Although hesitant to assign blame to any peers who may have already used the devices, "I can see no indication for which I would use a metal-on-metal hip implant over other options," panel chairman Dr. William Rohr said.
Patients with MoM total hip replacements who exhibit symptoms including pain, change in gait, swelling, new systemic signs/symptoms of metal toxicity, an orthopedic surgeon (preferably the one who placed the implant), rather than an internist, should evaluate the patient with X-rays and standard labs to rule out infections, the panelists agreed.
An MRI is indicated if lab work and X-rays suggest a problem with the implant, they said, but disagreed on the need for MRIs with all patients, regardless of symptoms. Some panelists argued that any MoM patient should be given the option of an MRI, but others said that there’s no need for such a costly diagnostic test in the absence of any symptoms.
There wasn’t enough data for a thorough analysis of metal ion testing data, according to the panel. Because these results are often confusing, there was no consensus on this diagnostic technique.
"Do you really need to have metal ion testing when you already have a diagnosis?" asked panelist Barbara Crouch of the University of Utah’s Poison Control Center. "Why get a test that may be confusing and muddy the picture?"
Metal-on-metal hips in the U.S.
Hip arthroplasty is intended to provide increased patient mobility and reduce pain by replacing damaged hip joints in patients who have enough sound bone to seat and support the components, according to the FDA.
There are 2 categories of MoM hip arthroplasty systems: Metal-on-metal total hip replacement systems, which consist of a metal ball to form the femoral head, a metal femoral stem in the thighbone, and a metal cup in the hip bone to make up the acetabular component; and metal-on-metal hip resurfacing systems, which consist of a trimmed femoral head capped with a metal covering and a metal cup in the hip bone to form the acetabular component.
Metal-on-metal total hip replacement systems are 1 of a variety of types of products available for hip replacement surgery and have been available in the U.S. for several decades, according to the agency. Metal-on-metal hip resurfacing devices have been available in the U.S. since 2006.
Five manufacturers currently market MoM total hip replacement systems in the U.S.: Johnson & Johnson‘s (NYSE:JNJ) DePuy Orthopaedics subsidiary, Biomet Inc., Encore Medical, Wright Medical (NSDQ:WMGI) and Zimmer (NYSE:ZMH).
Only 3 MoM resurfacing systems are currently approved in the U.S.: Smith & Nephew‘s (FTSE:SN, NYSE:SNN) Birmingham device, Corin Medical’s Cormet, and Wright Medical’s Conserve Plus.