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By Marilynn Larkin, Reuters Health
Certain metal-on-metal (MoM) hip replacement devices implanted after 2006 have an “unacceptably high” revision rate, due mainly to manufacturing problems, according to a new study.
“Although the use of MoM hip devices has declined dramatically in the past five years, hundreds of thousands remain in situ, with the long-term future uncertain,” Dr. David Langton, of University Hospital of North Tees in Stockton, UK, and colleagues wrote in an article online April 29 in BMJ Open.
To determine risk factors for revision in patients implanted with the commonly used DePuy Pinnacle MoM hip prostheses, the researchers identified all patients at the Stockton-based hospital who were implanted with a 36 mm MoM Pinnacle hip in conjunction with an S-ROM or Corail uncemented stem. They then identified only patients with components that had been implanted by either of the two senior authors of the study, Dr. Raj Logishetty or Dr. Antoni Viral Francis Nargol.
Implantations were performed from 2003-2009 and patients were monitored yearly. From 2007-2011, as awareness of the risk of adverse reactions to metal debris (ARMD) from MoMs increased, the hospital offered patients who developed symptoms blood metal ion testing and as-needed ultrasound scanning. From 2011 onward, given the widespread problems reported with MoMs, the hospital recalled all Pinnacle MoM patients for examination.
A total of 489 MoM Pinnacle hips had been implanted into 243 women and 191 men. Of these, 352 patients attended the MoM recall clinics and 64 died during the study period (mean follow-up, about 7.5 years). For the purposes of survival analyses, those who did not attend the recall clinics were assumed to have well-functioning prostheses.
A total of 71 hips were revised — an “unacceptably high” rate, according to the authors. All but one were carried out for ARMD, with one revision for a loose cup. Prosthetic survival rate for the cohort as a whole was 83.6% at nine years.
In 53 revisions (75%), “copious amounts” of fluid were found, and in 32 (45%), it was noted to be under pressure or had fistulated through the capsule. No abnormal fluid was identified at revision in only one case.
The researchers noted obvious damage to the abductor musculature in 38 cases. They documented a moderate-to-severe aseptic lymphocyte-dominated vasculitis-associated lesion on examination of retrieved tissues in 36 cases (51%). In 13 cases (19%), they found metallosis with no identified lymphocytic infiltration.
The majority of explanted devices showed signs of taper junction failure. A significant number of devices were found to be manufactured out of their specifications — a finding that was confirmed by an analysis of a wider data set from the Northern Retrieval Registry.
Risk factors for revision were bilateral MoM prostheses, smaller Pinnacle liners, and implantation in 2006 or later. Women were found to be at greater risk of early device failure. However, shell sizes and bearing diameters confounded the analyses, and liner size and/or earlier year of liner manufacture were determined to be greater threats to prosthetic survival than gender. The authors suggest that this analysis be repeated with input from an additional registry.
Dr. Langton, who is involved in litigation related to the Pinnacle device, told Reuters Health by email, “We have essentially shown that one of the major health care/orthopedic product manufacturers sold a product to surgeons and health care systems on the basis (that it was a) technologically advanced precision-engineered device, and it wasn’t precision-engineered.”
He added, “the product was produced in the same factories as (DePuy’s) other failed product, the ASR, which was . . . marketed on the same premise.” Mindy Tinsley, senior director, Communications and Public Affairs at DePuy Synthes Franchise, refuted the study findings. “We stand behind the strong record of safety and effectiveness of the (Pinnacle) ULTAMET Metal-on-Metal,” she told Reuters Health by email.
She added that “there are no manufacturing problems” with the device and noted that DePuy “questions the validity of the . . . paper given significant flaws in how it was conducted.” According to Tinsley, “measurements taken following an accepted international standard at the DePuy UK manufacturing facility” showed the device liners “were manufactured within specification.”
Dr. Mark W. Hungerford, director of Joint Replacement and Reconstruction at Mercy Medical Center in Baltimore, told Reuters Health by phone, “One study does not make or break anything in science. There have been issues in the field about MoM and early failure rates or not. That’s a serious issue being looked at by a lot of people. This is one more study showing a problem, but it’s not a definitive one.”
With respect to patients, “the obligation is no different than for any orthopedic device,” said Dr. Hungerford, who has not used the Pinnacle device. “All can fail, all need to be monitored for failure on a regular basis, and if problems arise, they need to be dealt with.”
The authors reported no funding. Dr. Langton, Dr. Nargol, and coauthors Dr. Thomas Joyce and Dr. Nick Cooke are retained experts for plaintiffs in ongoing MoM litigation. Dr. Langton and Dr. Nargol have worked with the U.S. Department of Justice in litigation involving DePuy.
For Further Information
More on the hip replacement device market in the United States can be found in a report suite published by iData Research entitled US Market for Orthopedic Large Joint Replacement Devices.