Reliability of microbiological diagnosis of prosthetic joint infection [PJI] strongly depends on the ability to dislodge microorganisms from biofilm and on the rate of contaminating samples during collection in the operating room and processing. The aim of a correct protocol is to avoid false negative and false positive results in order to adapt the correct therapy for each patient.

The object of the present study was to evaluate the impact of a novel closed bag system designed for samples collection and processing based on dithiothreitol (DTT), which is a sulfydryl compound able to remove bacteria from biofilm (MicroDTTect, 4i, Italy), on isolation of contaminant microorganisms in hip prostheses.

Specimens (prostheses, spacers, periprosthetic tissues) were aseptically collected according to a standard protocol into the device, which was transported to the laboratory for culture. Three different models of the system were prospectively evaluated, each being a development of the previous one. The first generation device consisted in an “open” system (DTT eluate was collected with a syringe and dispensed into sterile tubes), the second generation device in a “partially closed” system (DTT eluate collected directly in sterile vacuum tubes) and the third generation device in a “completely closed system” (DTT reservoir directly connected with sealed tubes inside the device). PJI was diagnosed following criteria established by MSIS.

The overall contamination rate, sensitivity and specificity of the first generation “open” system MicroDTTect were respectively 2.6% (1/39), 82.3% and 95.4% in 39 hips. The second generation “partially closed” device was characterized by a contamination rate of 1.96% (1/51), a sensitivity of 84% and a specificity of 96.1% in 51 hips. Contamination rate further decreased in the third generation “closed” system (1.89%, 2/106), while sensitivity (91.3%) and specificity (96.7%) improved in 106 hips. Differences have been also observed in hips (106) when compared to knees (70 cases) prosthetic infections (sensitivity 91.3% vs 89.3% and specificity 96.7% vs 100%).

Our data show as, thanks to its ease of use, low contamination rate and high sensitivity, MicroDTTect can represent a useful tool for improving the microbiological diagnosis of PJIs in hip revisions and has replaced sonication in our practice.