Sonication method improves diagnosis of prosthetic hip and knee infections

The new sonication method detected 14 more infections than standard tissue culturing.

Researchers at the Mayo Clinic in Rochester, Minn., have developed a new test that more accurately identifies the microbiologic cause of prosthetic joint infections.

The new test involves sampling bacteria from biofilms adhering to the prosthetic surface. After removing a prosthesis during revision arthroplasty, the device is placed into a container with 400 mL of Ringer's solution and subjected to a combination of vortexing and sonication.

The bacteria obtained from the sonication process are then incubated and quantitatively cultured, according to the study.

Andrej Trampuz, MD, and colleagues compared the efficacy of the new sonication method to conventional culturing for diagnosing the cause of periprosthetic joint infections in a study of 331 patients. The investigation included 207 revision total knee arthroplasty (TKA) and 124 revision total hip arthroplasty (THA) patients.

The researchers found that the new diagnostic test detected more cases of infection — 78.5% — compared to the conventional approach, which detected 60.8%, according to the study, which was published in the New England Journal of Medicine.

The sonication method detected 14 more cases of infection than the standard tissue culture method, the authors noted.

In addition, "In patients receiving antimicrobial therapy within 14 days before surgery, the sensitivities of periprosthetic tissue and sonicate-fluid culture were 45% and 75% (P<.001), respectively," they reported.

"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," Robin Patel, MD, Mayo Clinic professor of medicine and co-author of the study, said in a press release from the Mayo Clinic.

"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," she said.

For more information:
Trampuz A, Piper KE, Jacobson MJ, et al. Sonication of removed hip and knee prostheses for diagnosis of infection. N Engl J Med. 2007;357:654-663.