The purpose of this study is to analyze pre- and intra-operative joint aspirates of native joints and joints with suspicion of periprosthetic joint infection (PJI) of the hip, knee and shoulder acquired in clinical routine. Joint aspirates are then analyzed with new diagnostic methods (microcalorimetry, PCR, alpha-defensin, etc.). Diagnostic speed and accuracy of these methods is compared to standard diagnostic methods in clinical routine, such as blood cultures of joint aspirates, cell count/differential, intra-operative tissue culture and histology and sonication.

In this study, joint aspirate of patients that undergo joint aspiration in the context of routine pre- and intra-operative clinical diagnosis of a hip, knee or shoulder joint is collected. Routine joint punctures at our clinic are regularly performed in the emergency room, in the outpatient clinic and intra-operatively during diagnostic and revision surgery. A minimum of 5 ml aspiration fluid was required for inclusion in this study. Empty or diluted aspirations were excluded.

Joint aspirations are performed by orthopaedic surgeons with an 18-gauge needle according to standardized aseptic technique. Intraoperative punctures are performed prior to arthrotomy. A minimum of 1ml of joint aspirate is immediately transferred to a native study vial for our study, a native vial for gram stain and culture and a native vial for polarization microscopy, respectively. A minimum of 1 ml joint aspirate is transferred to an ethylenediaminetetraacetic acid (EDTA) vial for the determination of leucocyte count. Finally, a minimum of 1 ml is inoculated into a paediatric blood culture bottle.

Standard microbiological methods are performed in an external laboratory that routinely collaborates with our clinic. Leucocyte count is performed automatically with the mentioned EDTA vial. Polarization microscopy is performed at our pathohistological department in order to detect crystals and signs of infection in joint aspirate.

If written informational consent has been signed by the patient, the study vial is immediately transported to our internal laboratory for analysis with new diagnostic methods (microcalorimetry, PCR, etc.). When an immediate transportation was not feasible, the vial is stored in a cooling fridge at +3° C until transportation was possible.

Each case is individually reviewed and classified by an experienced infectiologist taking the case's clinical history and laboratory results into account.

Inclusion Criteria:

• adult of 18 or more years
• written consent to participate in study
• suspicion of septic arthritis or periprosthetic joint infection
• joint aspirate minimum of 5 ml

Exclusion Criteria:

• is not able to understand the aim or purpose of this study
• empty joint aspirate

Any patient with suspicion of septic arthritis or periprosthetic joint infection of the hip, knee and shoulder being diagnosed or treated in our facility in a clinical routine scenario willing to participate in this study (written informational consent)