New Test for Joint Infection
Posted 3/6/08
A potential diagnostic test that could help surgeons confirm or rule out the presence of infection-causing bacteria in prosthetic joints has been developed by researchers at the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS). Such a test could spare some people a time-consuming and costly treatment for infection. The test is described in the March issue of the Journal of Bone and Joint Surgery.
Each year, hundreds of thousands of joint replacement surgeries are performed in this country. And each year, thousands of them must be revised (the prosthetic joint must be removed and replaced) due to severe pain and swelling. These symptoms are often due to infection.
The standard treatment for suspected infection is to remove the joint prosthesis and replace it with a spacer that has been impregnated with antibiotics. After about six weeks, patients must undergo another surgery to remove the spacer. Only then can the surgeon implant the new prosthesis.
The problem with this approach is that confirming the presence of infection-causing bacteria is an inexact science. Currently, doctors check for infection by culturing a sample of the joint fluid. A positive culture confirms live bacteria, making spacer surgery a certainty. A negative culture, however, does not necessarily mean there is no infection. But because failure to treat an infected joint could lead to severe infection and limb amputation, spacer surgery is sometimes performed for safety's sake even when infection test results are inconclusive.
To get around the false-negative problem, Rocky S. Tuan, Ph.D., chief of NIAMS' Cartilage Biology and Orthopaedics Branch, and his colleagues developed a way to test for joint infections using reverse transcription polymerase chain reaction (RT-PCR) to test for bacterial messenger ribonucleic acid (mRNA).
Tuan's team now is recruiting 50 people who need joint revision for a clinical trial that will involve testing patients' joint fluid for bacteria and then following them for 6 months to a year after surgery. They hope that the results from this study will validate the protocol to identify or rule out infections before a person begins a surgical revision.
Tuan would like to be able to tell patients who need infection treatment, "There is a really bad infection and we know what to do. But we also want to tell the person without infection that it's O.K. to put in a revision joint. That saves the spacer, the additional surgery and its associated risk, and 6 weeks of being laid up," Tuan says.
Birmingham P et al. Simulated joint infection assessment by rapid detection of live bacteria with real-time reverse transcription polymerase chain reaction. J Bone Joint Surg Am 2008;90:602-08.
This article was adapted from a press release issued by the National Institute of Arthritis and Musculoskeletal and Skin Diseases.
