Abstract
Introduction
The utilization of sonicate fluid cultures (SFC) has been shown to increase the detection rate of periprosthetic joint infection (PJI) in comparison to the use of conventional microbiological methods, because sonication enables a sampling of the causative bacteria directly from the surface of the endoprosthetic components. The hypothesis of this study is that not only will the detection rate of PJI be improved, but also the detection rate of polymicrobial infection in patients with total knee arthroplasty (TKA) revision surgery.
Material and methods
74 patients which underwent TKA revision surgery received a synovial aspiration, intraoperative tissue cultures, histological sampling of the periprosthetic membrane, and sonication of the explanted endoprosthesis. A PJI was defined according to the following criteria: presence of intraarticular pus or a sinus tract, positive isolation of causative bacteria in ≥2 microbiological samples or a histological membrane indicative of infection (type II or III periprosthetic membrane).
Results
24 of the 74 patients had a defined PJI according to the above mentioned criteria. Through the use of multiple SFC it was possible to diagnose a PJI in three additional cases exclusively through SFC. In one case it was possible to achieve the required second bacterial isolation through SFC and fulfill the criteria for PJI. SFC achieved the highest sensitivity (88%) and specificity (74%) of all microbiological methods. The PM achieved a sensitivity of 79% and was also surpassed by SFC. When the results of the SFC and the PM were combined it was possible to correctly identify all cases of PJI.
Out of the 74 analyzed cases there were positive bacterial isolations in 40 cases. In 27 cases there were monomicrobial and in 13 cases polymicrobial isolations. From the 27 monomicrobial bacterial isolations 23 were detected through SFC and only 14 through conventional microbiological methods. 13 cases of monomicrobial bacterial isolations were exclusively identifiable through SFC. It is possible that these cases presented low grade infections and could therefore not fulfil the strict requirements for diagnosis of PJI.
In the 13 cases of polymicrobial bacterial isolations 2.6 bacterial species were isolated on average. 12 of these 13 cases were detectable through SFC and only 8 cases were detectable through conventional microbiological methods. 5 cases of polymicrobial isolations were detected exclusively through SFC. Additionally, it was only possible to detect the additionally isolated bacterial species through SFC in 4 cases.
Conclusion
In our study SFC was the most sensitive individual diagnostic method to diagnose PJI. The combination of SFC and PM achieved the highest sensitivity in our patient collective. The use of SFC increases the detection rate of polymicrobial PJI, which would be missed with the use of conventional microbiological methods.
