In the light of thousands of reports of injuries from metal-on-metal (MoM) hip implants, and the increasing number of lawsuits filed against such companies as DePuy Orthopaedics and Zimmer, Inc., the FDA’s Orthopaedic Surgery and Rehabilitation Devices Panel convened two days of public hearings.
The purpose of the meeting was to gather expert scientific and clinical opinions on the risks and benefits of these devices. The FDA hopes the meeting will provide the agency with guidance on future regulatory actions, as well as to provide healthcare professionals with guidance on managing patients who have received these devices.
The public has access to video of the actual meetings via an FDA website. The American Academy of Orthopedic Surgeons has also created a document that gives an overview of the scientific findings published as of July 15, 2011.
Summary of the Two-Day Meeting
The panel meeting took place at the Hilton in Gaithersburg, MD, from 7:30 a.m. to 7:00 p.m. on June 27th and 28th. On the first day, various experts agreed that revision of a failed MoM hip system is more challenging than revision of a failed metal-on-plastic replacement. Some panel members noted that the surgeon needs to be knowledgeable concerning the risks and benefits of all bearing surfaces, and needs to evaluate how these will apply to each individual patient. The panel also agreed that differences in gender – in that women respond differently to some implants than men – was a recurring concern.
On the second day, presentations focused on the challenges of evaluating patients with all-metal hips, since an early diagnosis of complications typically results in a more successful revision surgery. Tissue damage and pseudotumors are more prevalent in patients with these devices, and the experts debated on the best way to detect these issues early on.
In addition, the panel expressed concern about the limited data currently available to help doctors determine how the devices are performing, and whether or not they are causing metal contamination. They stressed the need for additional randomized controlled studies to help fill in the gaps.
Finally, at the conclusion of the second day, the panel discussed the importance of fully informing patients of the risks associated with MoM implants, as well as the importance of informing the surgeon of the difficulty of the procedure. Implanting a MoM device is reportedly much more difficult than implanting devices made of other materials.
Webcasts of the two-day meetings may be found at the following links:
An FDA Executive Summary Memorandum is also accessible, as well as the AAOS Technology Overview.
Problems with MoM Hips
According to the FDA summary, MoM systems are one of a variety of types of products available for hip replacement surgery. They were intended to provide longer-lasting joint replacements, but post-marketing reports found that during normal wear and tear MoM surfaces could shed metal ions of cobalt and chromium into the surrounding tissues and joint cavity. If the cup is not positioned exactly right, the risk of metal contamination goes up.
Patients can experience reactions to the metal ions, which can lead to tissue inflammation, tissue death, and bone loss. These, in turn, can culminate in pain, implant loosening, and device failure, leading to the necessity for revision surgery.
According to recent studies, MoM hips create a significantly higher risk of problems that lead to revision surgery than those made of other materials. Devices that may increase risk of metal contamination include the following:
- DePuy ASR hip system (recalled in August 2010)
- Zimmer Durom Cup (sales temporarily suspended in 2008)
- DePuy Pinnacle hip system (with metal insert)
- Biomet M2A Magnum
- Wright Conserve
- Wright Profemur Stem Designs
- Smith & Nephew Birmingham
- Proxima Hip
- Stryker MITCHTRH
- Stryker Rejuvenate and ABGII (these do not have a metal ball against a metal cup, like the others, but do place a metal modular neck inside a metal modular stem, creating the same risk of metal contamination)
- B. Braun Meisungen
- Revelation Lateral THR
- TriboFit Hip System
- MoM liners for use with FMP Acetabular System (made by Encore Medical, now DJO Surgical)
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