New Diagnostic Test Detects Infections in Knee and Hip Replacements

On Monday the Mayo Clinic announced that a team of Mayo researchers has discovered a new, more accurate diagnostic method of testing prosthetic joints, specifically knees and hips, to detect infection and potentially lead to improved treatment options and patient outcomes.

Nearly 800,000 total hip and knee replacement surgeries are performed each year in the U.S. During a 2006 presentation at the American Academy of Orthopedic Surgeons, it was estimated that the number of replacement surgeries will likely increase to 2.5 million by 2030, given the aging of the population and the continued advancement in hip and knee replacement surgeries.

Although the vast majority of patients who have total knee and hip replacement surgery experience good results, some find it necessary to undergo additional surgery because the prosthetic joint loosens or they develop an infection.

The method that's been used for years to detect prosthetic joint infection is done by sampling tissue around the prosthetic knee or hip joint at the time surgery is done. The new method is quite different and more accurate.

Dr. Robin Patel, a professor of medicine at the Mayo Clinic, led the multidisciplinary team of orthopedic surgeons, infectious diseases physicians and laboratory researchers who conducted the study.

Regarding the usual method used to detect infection, Patel said: "The problem with the conventional method is that you need multiple tissue specimens, because the sensitivity of a single specimen is not good - in other words, the infection might be missed with just one sample. Another issue is that bacteria normally found on the skin can be picked up on the tissue specimen as it is extracted and passes through the skin, yielding a false-positive result. These same bacteria may actually cause the infection, so doctors can't always tell just by the type of bacteria detected whether the patient has an infection or not. If multiple specimens are positive for the bacteria, then this indicates that the bacteria are causing the infection."

The new method samples bacteria that adhere to the prosthetic surface. In the study, the method was tested on 331 patients with prosthetic hip or knee joints who were having their prosthetic joints removed because of either infection or another problem. Simply put, the prosthetic knee or hip joint was surgically removed. The prosthetic was then sent to the laboratory, where a solution was added to the container with the prosthetic. The container was shaken and exposed to ultrasound, which is known to remove biofilm bacteria. The bacteria remained in the solution and was then identified.

The new test detected 78 percent of the infected joints; the conventional method detected 61 percent. The findings of the study are published in the August 16 issue of the New England Journal of Medicine.

Dr. Patel said if one looks at the study, "you'll see we found a wide variety of different types of bacteria. This is important to recognize, because it is ideal for the doctors to know what type of infection they are dealing with in order to treat it properly - this determines what type of antibiotic to give, and in some cases, what type of surgery to perform."

Dr. Patel said that some people with prosthetic joints may not know they have an infection. Patel explained that "when people think of infection, they may think of fever or pus coming out of a wound. However, this is not the case with prosthetic joint infection. Patients will often experience pain, but not other symptoms usually associated with infection. Often what happens is that the bacteria that cause infection on prosthetic joints are the same as bacteria that live harmlessly on our skin. However, on a prosthetic joint they can stick, grow and cause problems over the long term. Many of these bacteria would not infect the joint were it not for the prosthesis."

This new diagnostic test is now standard procedure at Mayo Clinic, which has an unique Orthopedic Infectious Disease group that cares for and treats patients with prosthetic joint infections. Mayo Clinic also holds the patent for the new test.

Source:

Press release, Researchers Discover New Diagnostic Test for Detecting Infection in Prosthetic Joints; http://www.newswise.com/articles/view/532403/