Due to the ageing society, the number of arthroplasties as well as revision arthroplasties and periprosthetic joint infections (PJI) are increasing requiring an evidence based diagnostic and therapeutic regime [1,2]. Recently, a mortality rate of about 20% within 5 years was shown in patients suffering from PJI [3,4]. Nevertheless, there is no consistent definition of PJI yet. Most definitions rely on the combination of different parameters giving major and minor criteria in order to stratify the risk for PJI [5]. However, in addition to appropriate antibiotics the radical debridement is the most important step in the effective therapy of PJI [6]. Surgical therapy can be further divided into one-stage and multistage revisions with various periods of antibiotic therapy in-between [7]. In Germany, mostly a period of 4–8 weeks is set between removal and reimplantation of the prosthesis. Spacers made of bone cement containing antibiotics (PMMA spacers) can be used to fill the dead space in periods between removal of the infected prosthesis and reimplantation and are applied in 90% of two-stage revisions in EndoCert-Centers in Germany [5]. This is a very critical period since there is no valid method to clarify infection persistence. Additionally, the success rate of failed two-stage revision is poor with infection control in only 60% [8]. Therefore, a reliable diagnosis of persistent infection is mandatory for a positive outcome. Otherwise, an unnecessarily prolonged therapy regime with multiple revision surgeries and extended antibiotic therapy is not only a significant physical and psychological burden for the patient but also have serious economic consequences [9,10]. Currently, there is no single reliable method to identify infection persistence and to determine the adequate time for reimplantation. Usually, improvement of clinical symptoms and decrease of serological inflammatory parameters like CRP and ESR are used as values for infection eradication although they often remain elevated [11]. Equally, arthrocentesis is frequently performed before reimplantation of the prosthesis despite inconclusive evidence concerning the diagnosis of persistent infection [12,13]. Another option is the use of drain fluids in the detection of infection persistence. Drains are commonly used after revision arthroplasties and therefore do not require an additional invasive procedure. Furthermore, samples can be taken directly after the initial revision surgery allowing the detection of infection persistence in an early state. So far, studies relating to infection detection by the analysis of drain fluid or drain tips [14,15] are outdated since the microbiologic techniques have been continuously refined in the past decades [16].

In the current study, we performed a microbiologic analysis of drain fluid in the treatment procedure of PJI to validate their significance in the diagnosis of PJI persistence in multistage surgery. We hypothesize that the microbiological analysis of drain fluids after revision surgery is a reliable method to determine infection persistence in PJI.