Published March 05, 2012
Infection poses one of the most serious risks to patients getting a hip or knee replaced, and a major U.S. drugmaker is developing a test to quickly identify the pathogens responsible so doctors can treat problems sooner.
Abbott Diagnostics Group, a unit of Abbott Laboratories, is working with privately held Genetics Laboratory Inc, whose expertise is in orthopedics, to develop the test.
It will be based on Abbott's PLEX-ID system for identifying microbes, and is expected to help doctors detect infections that become rooted in the body's joints long before they become apparent through physical symptoms.
"This is a completely new way of diagnosing infectious disease," Dave Ecker, divisional vice president at Abbott Molecular, said in an interview. "It is currently dominated by technology using cultures, which is a 150-year-old technology. We are long overdue for an advance."
Once Abbott and Genetics Laboratory build the test, an application specific to identifying orthopedic infection would require approval from the U.S. Food and Drug Administration, which could take 5 years, Ecker said.
"Orthopedics is one of the leading opportunities for this technology because of what it's able to do for patients who have orthopedic infections, which are difficult to diagnose by conventional methods," Ecker said in an interview.
"But it has broader applications. This is a one-stop shop for infectious disease," he said, referring to illnesses from blood stream and respiratory infections, to influenza.
About 800,000 knee and hip replacement procedures are performed annually in the United States, and complications related to infections occur in about two percent of those procedures, according to a 2009 study published in the New England Journal of Medicine.
More than 70,000 joint revisions are performed annually in the United States, with more than 15 percent of hip and 25 percent of knee revisions caused by infections. Revisions are often more expensive and complicated than the original surgery.
PLEX-ID was originally used by U.S. government biodefense researchers who wanted to rapidly identify pathogens used in a potential bioterrorism attack. The PLEX-ID system can identify a broad variety of pathogens within 5 to 6 hours by weighing the DNA of the microorganism.
In orthopedic cases, the standard method of identifying pathogens is by taking a culture, which can take several days to grow and produce a result. Blood tests and joint fluid analysis can also give clues about the presence of an infection, but results can take time and may be inconclusive.
Dr. Javad Parvizi, an orthopedic surgeon at the Rothman Institute in Philadelphia, noted that infections are a risk during surgery itself, but may also occur a decade after a knee or hip replacement. He is not involved in the Abbott venture.
About 4 percent of hip and knee replacement patients suffer infection within the first 10 years after the procedure. Prosthetic joint infection is the number one cause of knee replacement failures and the second most common cause of hip replacement failures, he said.
Infections in joint replacements have been on the rise, partly because of the growing number of people with prosthetic implants and the fact that detection has improved. But patients are also at higher risk because there are more antibiotic-resistant bacteria lurking around hospitals, said Parvizi.
Abbott's PLEX-ID can identify bacteria, viruses, fungi and certain parasites. It also provides information on drug resistance, virulence, and strain type. It is already used in the European Union to identify influenza after it has been grown in a culture.
During a procedure to replace a joint, the surgeon may take a tissue sample and test it for infection as a precautionary measure. After the procedure, if the patient has symptoms, such as swelling near the surgical site, the surgeon may extract fluid from the joint and test it for infection.
Bacteria -- particularly antibiotic-resistant types such as Methicillin-resistant Staphylococcus aureus, or MRSA -- can be tricky to detect because the bacteria form slimy colonies on the surface of the joint implant, said Dr. Gerhard Maale, an orthopedic oncologic surgeon based in Dallas, Texas. He will serve as the medical director for the collaboration.
These biofilms are difficult to identify with a traditional bacterial culture because the organisms clump together and do not grow well enough for positive identification, he said.