Tuesday, January 16, 2018

A synovial fluid test for infected joint replacements

The Accuracy of the Alpha Defensin Lateral Flow Device for Diagnosis of Periprosthetic Joint Infection Comparison with a Gold Standard

These authors examined the accuracy for the detection of periprosthetic hip and knee infections (i.e. those meeting the criteria established by the Musculoskeletal Infection Society) of a rapid lateral flow version of the alpha defensin test in a aspirate of synovial fluid.

The study group included patients with pain after total hips or total knees. There were 119 joints with an aseptic revision and 76 joints with periprosthetic joint infection according to the MSIS criteria (Clin Orthop Relat Res (2011) 469:2992–2994)

The overall sensitivity of the Synovasure Alpha Defensin Test was 92.1%, the specificity was 100%, the positive predictive value was 100%, and the negative predictive value was 95.2%. The overall accuracy of the Synovasure test was 96.9%.

The culture results of the aspirates are shown below.

The authors conclude that the "Synovasure Alpha Defensin Test with a lateral fl ow device demonstrates encouraging results with high accuracy for diagnosing infection following total hip arthroplasty and total knee arthroplasty. However, the test is associated with high costs, which is a limiting factor. Further cost-benefit studies will determine if the high costs of this new tool are justifiable."

Comment: With respect to the use of such a study in the evaluation of patients with pain after a shoulder arthroplasty, we must recall that a high percentage of these patients have positive deep tissue and explant cultures for Propionibacterium but do not meet the MSIS criteria for a periprosthetic infection. It is well recognized that the stealth presentation of a failed shoulder arthroplasty with positive cultures can occur months or years after the joint replacement. It would be of interest to learn the sensitivity of this new test in the evaluation of these patients.