Metal on Metal Hip Corrosion is Industry-Wide Problem No topic in orthopedic technology covered b

Metal on Metal Hip Corrosion is Industry-Wide Problem
No topic in orthopedic technology covered by the “popular press” (as Young-Min Kwon, M.D., calls it) has received greater attention over the past few years than metal on metal (MoM) implants. And while certain implants, such as DePuy Synthes’ ASR hip implant or Zimmer’s Durom hip, have gotten a bad rap, the problem is industry-wide and “we shouldn’t get caught up on any one particular implant,” according to Herbert J. Cooper, M.D., of New York, N.Y.

Kwon moderated a symposium at the 2014 Annual Meeting of the American Academy of Orthopaedic Surgeons (AAOS) on the clinical impact of MOM and modular corrosion.

In February, the New York Times proclaimed in a headline: “As seen on TV, a medical mystery regarding hip implants is solved.” The article reported that Juergen R. Schaefer, M.D., a University of Marburg, Germany physician, found the answer to an “arcane medical mystery” on an episode of House, a television show about a cantankerous “diagnostician” (not a real field of specialization) who diagnoses so-called undiagnosable patients by using Sherlock Holmes-like methods of deduction.

The real-life mystery was this: a German man started experiencing low thyroid hormone levels, inflammation of his esophagus and fever of unknown origin. His senses were impaired so badly that he was almost blind and deaf. Most troubling, his heart had weakened so much it could not pump hard enough to supply blood to his body. He was going from doctor to doctor, and no physician could find the root cause of his ailments. Coronary disease usually results in heart failure, but his arteries were fine and physicians had no idea why.

Dr. House had a middle-aged female patient who presented with very similar symptoms. House’s diagnosis? Cobalt poisoning from her artificial metal hip. After testing, Shaefer found that cobalt poisoning indeed was the reason for his patient’s mysterious ailments. His cobalt levels were more than 1,000 times higher than normal levels. However, the reason for the corrosion was attributed to a failed ceramic hip. It was removed and replaced with a metal hip, but tiny particles of the ceramic material were left behind in his hip socket. Those particles acted as sandpaper and wore away the cobalt, poisoning his entire body, not just the surrounding tissue.

The case shows that it’s not simply a MoM implant problem when it comes to metal poisoning. It also can be freak incidents from prior surgeries or surgeon error.

It is important to note that despite extensive media coverage and now, hundred of lawsuits, acute metal toxicity due to prosthesis malfunction is a very rare event.

Retrieving explanted orthopedic devices that failed due to corrosion for testing is invaluable, said Alister Hart, M.D., F.R.C.S., professor of orthopedic surgery at University College London (UCL) in the United Kingdom.

“They are like the black box of an aircraft,” Hart said. “They really help us understand the cause of failure. For instance, one percent of LIRC (London Implant Retrieval Centre) retrieval cases are a component size mismatch.”

In other words, surgeon error.

Hart co-founded UCL’s LIRC, which collects explanted devices to study reasons for failure. The LIRC evaluates implants with five levels of knowledge: possession of the implant only; possession of the implant plus intra-operative details; all of the above plus clinical and blood details of the patient; all of the above plus implanted device imaging details; and linkage to registry. At AAOS, Hart presented data from 2,500 implants retrieved since 2008.

“With more, we can say more,” Hart said with regards to the importance of implant and patient history. “I can assure you that the measurement of these devices is now highly reliable … so we can now say that there is some sort of patient susceptibility factor contributing to wear.”

Hart also noted that implant linkage to the registry “improves post market surveillance and the ability to safely innovate.”

“Of great interest is adverse local tissue response,” said Robert M. Urban, describing a study that compared adverse local tissue (ALT) MoM responses with ALT metal on polyethylene responses and found that tissue damage was similar. “Such intense inflammation always leads to necrosis. We see this in corrosion of head neck junctions. We must also be mindful of systemic dissemination—metal ions and particles in the liver and spleen, lymph nodes and bone marrow. Our present work is with bone marrow: we’ve been finding particles in the spine, sternum, ribs and ends of long bones.
However, it is important to note that distant organ dissemination only happens when there is a high concentration of particles.”

The panel also presented several case studies of corroded hip implants in patients of different demographics. More than 50 percent of retrieved failed titanium alloy neck stems of hip implants showed at least mild corrosion. The risk remains a concern for both patients and orthopedics patients, and surgeons in the audience agreed vociferously with the suggestion that surgeons should be extremely vigilant with MoM implants, making sure that any possible risk of failure through error or implantation into high-risk patients is minimized.

Craig J. Della Valle, M.D., of Chicago, Ill., noted that young female patients remain the most at-risk hip resurfacing patients. The potential for them to become pregnant puts them at great risk for failure, and studies conclude they should be more educated in the risk of hip implant procedures or avoid the procedure if possible.

The AAOS presentation abstract concluded that high level metal exposure following joint replacement is rare, associated with prosthesis malfunction, and very rarely is associated with acute illness, mainly affecting neurological, cardiac, and thyroid health. It is likely that metal levels well in excess are required (in otherwise healthy patients) before systemic manifestations are seen. Low elevated metal exposure is extremely common, and may associate with structural and functional differences affecting bone, the brain, and heart. However, these effects are subtle. Longer-term study is required in the patient group that has implanted metal hips to determine whether clinical disease could emerge over the full service lives of these products.

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