Study design:
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 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.
Table 1: 2018 Definition of periprosthetic hip and knee infection
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 . Metallosis, other inflammatory comorbidities, and previous or concomitant antibiotic therapy were considered as exclusion criteria.
Patients:
From July 2018 to June 2019, 47 patients identified as having an aseptic joint effusion according to the Definition of Parvizi et al. (2018) were included into the study. The group included 27 women and 20 men with a mean age of 66 ± 12.5 (38–88) years. There were 18 knees, 27 hips and 2 shoulders. The group consisted of 45 patients with polyethylene wear debris induced osteolysis and 2 hips with corrosion of modular head-neck junction. The mean BMI (Body Mass Index) was 26.7 ± 3.1 (22–37).
In the same period, 23 patients were classified as having a PJI according to the Definition of Parvizi et al. (2018). The group consisted of 15 women and 8 men with a mean age of 72 ± 11.3 (47–89) years. There were 3 knees, 17 hips and 3 shoulders. The mean BMI was 27.1 ± 7.3 (19–45). In 16 aspirations joint fluid was tested positive in microbiological culture. Bacteria were identified in 16 (70%) of 23 patients of the infection group. Staphylococci were found in 11 (69%), Propioni bacteria and and Enterococci in each two (13%) and Serratia marcescens were found in one (6%). In 7 patients (29%) in the infection group with positive histologic specimens for infection, no bacteria could be isolated after 14 days incubation.
Sample Preparation
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:
Serum 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%). Synovial 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)).
Statistical Analysis:
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, and their 95% confidence interval (CI) for any cut-off level were calculated.