After approval of the institutional review board (18-8042-BO), a prospective study was performed of data gathered from Department of Orthopedics and Trauma Surgery from University of Duisburg-Essen, Germany, in patients with persisting pain[i] after hip, knee and shoulder arthroplasty.
All patients signed informed consent forms prior to being enrolled. The study was conducted in accordance with the declaration of Helsinki.
Medical history, clinical examinations, laboratory values including C-reactive protein (CRP) and joint aspiration fluid were gathered preoperatively as routine diagnostic procedures. Based on the findings of the preoperative diagnostic tests, the patients were considered as aseptic or septic according to the 2018 Definition of periprosthetic hip and knee infection[ii].
The study focused on the differentiation between low-grade infects and aseptic cases. According to WAIOT definition patients without two or more signs or symptoms of local inflammation (pain, swelling, redness, warmth, function laesa) were classified as low-grade infects [iii]. In order to determine the impact of renal dysfunction on serum and synovial values of PCT, serum creatinine concentrations were gathered at the time of joint puncture.
Inclusion criteria were a sufficient amount of synovial fluid for all determinations, and full clinical and laboratory data to allow for diagnosis of periprosthetic infection (PJI). Patients were further excluded, if they showed signs of early postoperative PJI (8 weeks) due to lack of reliability of synovial and serologic markers shortly after surgery [iv][v]. Metallosis, other inflammatory comorbidities (HIV, rheumatic diseases), and previous or concomitant antibiotic therapy were considered as exclusion criteria.
All patients gave their written informed consent that surplus material of their blood and synovial samples which is not needed for standard diagnostics is used for research studies.
Blood was taken from the cubital vein the day before surgery. Synovial aspiration was executed avoiding an admixture of blood with an 18-gauge needle. Synovial fluid was aseptically aliquoted into sterile tubes and centrifuged for 8 minutes at 4°C with 2000 g. The synovial fluid samples were put on ice and transported within 60 minutes to Laboratory of Institute of Medical Psychology and Behavior Science University of Duisburg-Essen and frozen at −80° C.
Determination of the Levels of Serum and Synovial Fluid biomarkers:
S-PCT levels were quantified under the use of immunoassay (Centaur, Siemens, Germany) with lower limit of detection of 0.02 ng/mL (normal < 0.5 ng/mL). Serum CRP was analyzed by immune turbidimetry (Centaur, Siemens, Germany) (normal < 0.5 mg/dl). Synovial leukocyte level and percentage of polymorphic neutrophils was measured by flow cytometry with EDTA plasma (normal range, <3000/µl and <80%). SF-PCT levels were measured using a standard quantitative PCT enzyme immunoassay kit, according to the manufacturer´s instructions (Anti-Procalcitonin antibody ab166963, ABCAM, Cambridge,UK). Synovial alpha-1-Defensin was analyzed using a standard quantitative enzyme immunoassay kit (Human α-Defensin 1 Antibody, R&D Systems Bio-Techne, Minneapolis, USA)(cut-off level 4800 ng/mL). The results were given as standardized signal relative to a tolerance limit value (interpretation values: < 0.9 aseptic, 0.9–0.99 unspecific, ≥ 1.0 septic). Synovial CRP was analyzed under use of a quantitative enzyme-linked immunoassay (CRP ELISA (EU59131), IBL International GmbH, Hamburg, Germany)(cut-off level (> 6,9 mg / l)).
The data were processed with the statistical software package SPSS. Basic descriptive statistics were used to analyze clinical and laboratory values. Normally distributed continuous data were shown as mean ± standard deviation (SD) and compared using student's t-test. Non-normally distributed continuous data were shown as mean and compared using the Mann–Whitney U test. A p value < 0.05 was considered statistically significant. Sensitivity, specificity, area under the curve (AUC) and their 95% confidence interval (CI) for any cut-off level were calculated via receiver operating characteristic (ROC) analysis.