Ultrasound Improves Infection Diagnosis in Hip and Knee Prostheses

ROCHESTER, Minn., Aug. 16 -- For microbiologic diagnosis of an infected hip or knee prosthesis, low-energy ultrasound of the device itself may be the preferred approach.

In a study of 331 such patients, the sensitivity of sonicate-fluid culture proved superior to that of tissue culture, especially in patients previously treated with antibiotics, Robin Patel, M.D., of the Mayo Clinic here, and colleagues reported in the Aug. 16 issue of the New England Journal of Medicine.

Culturing samples of periprosthetic tissue, the standard method for the microbiologic diagnosis of prosthetic joint infections, is neither sensitive nor specific when the pathogens are harbored by the device itself, the researchers wrote.

In these infections, microorganisms are encased in a biofilm on the surface of the prosthesis, which suggested that using ultrasound to dislodge adherent bacteria would improve diagnosis. Sonication is kept at a low level to preserve microbial viability.

In a prospective trial of a more practical way to do this by the Mayo clinicians, comparing conventional culture with cultures of samples obtained by sonication, the researchers studied 207 patients with total knee prostheses and 124 with hip prostheses undergoing removal of the prosthesis for aseptic failure or presumed infection.

Of the patients, enrolled from Aug. 12, 2003 to Dec. 13, 2005, 252 had apparent aseptic failure (median age 70), and 79 had prosthetic-joint infection (median age 68).

Using standardized nonmicrobiologic criteria to define prosthetic joint infection, the researchers found the sensitivities of periprosthetic tissue cultures and sonicate-fluid cultures were 60.8% and 78.5% (P

Dr. Waldvogel listed three study limitations. First, he said, the diagnosis of aseptic failure was established by conventional criteria, but the sonication method may have been suboptimal in efficiency, he said, and the prostheses may have been misclassified.

Second, the researchers used conventional microbiologic techniques, but newer techniques have been used to detect bacteria in sonicate fluid from prosthetic hips, and the results have been impressive.

Third, clinicians are often confronted with the question of possible infection before, and not during, surgical intervention. Unfortunately no test is currently available to answer this important question.

Despite these limitations, Dr. Waldvogel wrote, the procedures already used for the diagnosis of catheter-related infections may soon become a standard approach for all infections suspected of being associated with prosthetic material.

"Ultrasound technology not only is diagnostic imaging -- sound for sight -- but also may improve microbiologic diagnosis of a vexing clinical problem: sound for bugs," he concluded.

Dr. Patel, and certain of the other co-authors reported having an unlicensed U.S. patent pending for a method and an apparatus for sonication. Dr. Patel reported receiving consulting fees from Celleration and Johnson & Johnson, test-development royalties and license fees from Roche Diagnostics, and research support from Pfizer, Cubist, Celleration, Bristol-Myers Squibb, Arpida, Basilea, and Johnson & Johnson.

Other authors reported receiving research support, consulting fees, advisory board fees, royalties, institutional financial support, and other forms of remuneration from Hawkins, Cubist, 3M, Ortho-McNeil, Elan, Wyeth, Smith & Nephew, Roche Diagnostics, Virco, and bioMrieux. The Mayo Clinic reported receiving institutional financial support from Hawkins. No other potential conflict of interest relevant to this article was reported.

Dr. Waldvogel, the editorial writer, reported serving on the board of Novartis Venture Fund. No other potential conflicts of interest relevant to this article were reported.