FDA Panel Has No Answer for Metal-on-Metal Implant Problem
Metal-on-metal (MoM) hip implants have been under the microscope ever since 2010, when studies including one that appeared on the online version of the Journal of Bone and Joint Surgery indicated problems with cobalt toxicity. All-metal hip implants are commonly constructed of cobalt-chromium alloy. Around the same time, The Journal of Arthroplasty warned doctors to use the MoM devices only with “great caution, if at all.” Those most likely to suffer negative reactions to MoM implants are women and overweight patients.
In early 2010, the New York Times started reporting the reluctance of many orthopedic surgeons to perform MoM hip implants amid concerns of severe tissue and bone damage in some patients. There were rumblings in the orthopedic medical community in years preceding 2010 of the tendency of MoM hip implants to wear quickly, depositing large amounts of metal debris in the body, leading to toxicity.
Concern has continued to rise. In February, the United Kingdom’s Medicines and Healthcare products Regulatory Agency published a Medical Device Alert, advising that patients with MoM hip implants sized 36 mm or larger follow more aggressive follow-up schedules. In the United Kingdom, regulators advise patients with MoM implants to get yearly blood tests whether they are experiencing adverse symptoms or not.
There have been two major MoM total hip replacement device recalls in the United States. Zimmer Holdings voluntarily recalled its Durom Acetabular Component in 2008 because of inadequate directions on the labeling. Then in 2010, Johnson and Johnson subsidiary DePuy Orthopaedics recalled its ASR total hip systems due to a high number of revision rates from registries outside the United States. The Durom is now available with more detailed surgical technique instructions and a surgeon training program, but the ASR never returned to the market.
On June 28, the U.S. Food and Drug Administration (FDA) concluded a two-day expert advisory panel meeting evaluating the safety of the MoM implants. The 18-person panel discussed current knowledge about the safety and effectiveness of MoM hip arthroplasty systems. According to the FDA, the group was convened to seek expert scientific and clinical opinion on the risks and benefits of these types of devices based on available scientific data.
The American Academy of Orthopaedic Surgeons had representatives on the panel, as did the medical device manufacturing industry (Biomet’s Robert E. Durgin, J.D.) and consumers (Connie Whittington, M.S.N., R.N., of Peachtree Orthopaedic Clinic). Barbara Berney served as the patient representative present.
Despite the two 12-hour sessions, however, no conclusive advisories have been forthcoming.
Presented with a plethora of information, panel member Scot Evans, Ph.D., had this to say: “the issue is that it's from observational studies and registries that are not optimally designed to answer the very, very difficult questions we've been trying to hassle with today.” Evans is a Harvard University biostatistician.
Meeting Chair William Rohr, M.D., of Mendocino Coast District Hospital said, "I do not use metal-on-metal hips, and I can see no reason to do so."
Polymer and ceramic are the long-used traditional materials for hip implants. The reason surgeons moved to metal was because of the suggestion that they would be more durable. Their hardness has backfired, however, as they cause tissue damage for the very same reason some medical practitioners were attracted to them in the first place.
“No single bearing surface meets the needs of all patients,” said Paul Voorhors of DePuy Orthopaedics. “Not all metal-on-metal products are the same, and each should be evaluated on its own merits.”
“Metal-on-metal, ceramic-on-ceramic and metal-on-ceramic are unforgiving couples,” said panel member Michael B. Mayor, M.D., of Dartmouth Medical School’s Thayer School of Engineering. “They all show evidence of impact loads delivered by the edge of the acetabular component onto the surface of the head in the form of edge stops and gouges. Those are fairly severe alterations of articular surface.”
On the final day of the sessions, panel experts said that patients with MoM implants complaining of pain should get regular X-rays and blood tests for metal levels. However, as the panel acknowledged, there are problems with blood test accuracy and interpretation of the results. Currently, there are no standard tests for chromium.
In his concluding remarks, Rohr tried to consolidate the overall opinion of the panel. He recommended that the FDA look into additional labeling regarding the technical difficulty of implantation, as well as warnings to patients that both pseudo-tumors and elevated metal ion levels have been reported in both symptomatic and asymptomatic patients.
These recommendations are still less aggressive than many that are already in place overseas. The FDA has not yet implemented or endorsed any of these recommendations, suggesting that the administration may need to parse through the information and opinions presented by the professionals on the panel.