gms | German Medical Science

Objectives: An accurate diagnosis of periprosthetic joint infection (PJI) is essential for successful treatment. Joint aspiration is the standard pre-operative diagnostic procedure. However, conventional cultures are time-consuming and/or lack accuracy. Microcalorimetry, a detection method of microbial growth-related heat production, has been shown to improve the diagnosis of septic arthritis, but has not yet been evaluated in prosthetic joints with different microbiology and pathogenesis.

Methods: Synovial joint aspirates were prospectively obtained in patients with suspected PJI of the hip or knee from October 2015 until January 2015 in our facility. Diagnosis of PJI was established when at least one of following criteria applied: prosthesis explantation, acute inflammation in intraoperative periprosthetic tissue, growth in synovial fluid or intra-operative tissue culture, >2000 leukocytes/mm2 or >70% granulocytes in synovial fluid. Synovial fluid was aspirated before or during surgery and analyzed by gram stain, culture (incubation 14 days), leucocyte count and microcalorimetry (incubation minimum 5 days). Sensitivity, specificity, positive (PPV) and negative predictive value (NPV), accuracy of each test and the time to positivity for microcalorimetry was determined and a binomial test was employed to find significant differences between the test results.

Results and Conclusion: 66 patients were included in the prospective cohort, of which 30 (46%) were diagnosed with PJI. The following microorganisms were found: Staphylococcus aureus (n=1), Staphylococcus epidermidis (n=1), streptococci (n=3), E. coli (n=1) and enterococci (n=1). The synovial cell count demonstrated a high sensitivity (95%) and specificity (83%), PPV 78%, NPV 96%, accuracy 88%. Synovial fluid cultures vs. microcalorimety showed sensitivity 33% vs. 26%, specificity 95% vs. 100%, PPV 82% vs. 100%, NPV 67% vs. 66%, accuracy 70% vs. 70%, respectively. Prosthesis sonication vs. intraoperative tissue cultures showed sensitivity 70% vs. 43%, specificity 67% vs. 75%, PPV 88% vs. 69%, NPV 88% vs. 50%, accuracy 40% vs. 57%, respectively. When comparing microcalorimetry to aspiration culture with a binomial test, no significant differences (p=0,25) could be found between the obtained test results, while sensitivity was 78%, specificity 100%, PPV 100%, NPV 97%, and accuracy 97%. The median time until positivity of microcalorimetry was 8.6 hours.

In conclusion, this is the first report of microcalorimetry in prosthetic joints. The accuracy of microcalorimetry was comparable with that of aspiration culture (97%), while microcalorimetry was faster (<9 hours until positivity). Microcalorimetry of synovial fluid obtained promising results and allows rapid diagnosis of PPI. However, intraoperative tissue and sonication cultures remain superior to aspirated synovial fluid cultures.