Difficulty of diagnostic accuracy of periprosthetic joint infection

\(\bf Background\) Diagnostic accuracy of periprosthetic joint infection still remains controversial and an unsolved problem with respect to clinical signs and laboratory measures. Influencing factors of diagnosis like age, sex, abnormal physical findings and comorbidities are published with different results. The aim of our study was to find factors strengthening the diagnosis. \(\bf Methods\) We therefore retrospectively investigated all revision surgeries of total knee arthroplasty and total hip arthroplasty in the years 2019 and 2020 in a tertiary hospital with special regard to diagnostic accuracy of periprosthetic joint infection and switch in diagnosis to aseptic mechanical loosening or vice versa. All patients were divided into 4 non-hierarchical groups: suspected and discharge diagnosis periprosthetic joint infection (P1), suspected and discharge diagnosis mechanical loosening (P2), suspected diagnosis mechanical loosening and discharge diagnosis periprosthetic joint infection (P3), suspected diagnosis PJI and discharge diagnosis mechanical loosening (P4). \(\bf Results\) In the years 2019–2020, 106 patients underwent revision surgery of total knee arthoplasty and total hip arthroplasty. 33 patients showed periprosthetic joint infection (31.1%) according to Infectious Diseases Society (IDSA) criteria, 73 patients showed mechanical loosening (68.9%). Of the periprosthetic joint infection -patients, 15 were men (46%) and 18 were women (54%). The patients with mechanical loosening were 27 men (37%) and 46 women (63%). In group P1 (25 patients), 22 could be classified according to the histopathological classification Krenn and Morawietz grade 2 and grade 3, 2 patients to grade 4 and one patient could not be classified. In group P3 (8 patients) all could be classified according to the classification Krenn and Morawietz grade 2 and 3. Groups P1 – P4 were correlated with categorial basic data: All Groups P1 – P4 showed a statistical correlation towards American Society of Anesthesiologists (ASA) categorization 3–4 versus ASA 2 (\(\it p\) = 0.01). In the pairwise comparison in the exact Fisher's exact test P1 and P2 showed a statistical correlation towards ASA categorization 3–4 versus ASA 2 (\(\it p\) = 0.01). Charlson Comorbidity Index (CCI) categories 5–7 versus 0,1–2 and 3–4 showed a statistical correlation towards groups P1-P4 (\(\it p\) = 0.007) and in the pairwise comparison in the exact Fisher's exact test a discrimination of P1 and P2 (\(\it p\) = 0.001) and P1 and P3 (\(\it p\) = 0.007). The preoperative corticoid therapy showed a statistical correlation to groups P1-P4 (\(\it p\) = 0.05) and in the pairwise comparison in the exact Fisher test a discrimination of P1 and P4 (\(\it p\) = 0.02). \(\bf Conclusion\) We therefore conclude that diagnosis of periprosthetic joint infection still remains difficult. Switches in diagnosis during hospital stay from periprosthetic joint infection to aseptic mechanical loosening and vice versa are not unusual and the role of different diagnostic tools needs further investigation. Patients categorized according to ASA and CCI as severely ill might be more likely to be diagnosed correctly with periprosthetic joint infection.