Clinical and Histological Features of Prosthetic Joint Infections May Differ In Patients With Inflammatory Arthritis and Osteoarthritis

Abstract Background: Inflammatory arthritis (IA) patients are at increased risk for prosthetic joint infections (PJI); however, diagnosis is challenging because active IA patients have elevated inflammatory markers that may mimic joint infection and definitive microbiologic diagnosis may be delayed. The objective of this pilot study was to identify the clinical, microbiologic, and histopathologic features of culture positive (CP) and culture negative (CN) total hip (THA) and total knee arthroplasty (TKA) PJI in IA patients and obtain preliminary data to support a definitive study to determine the optimal method for PJI diagnosis in patients with inflammatory arthritis. Methods: A retrospective cohort of THA/TKA PJIs, from 2009 to 2016, were identified using an institutional PJI registry. H&E slides of OA and IA PJI cases matched by age, sex, and culture status were histologically reviewed. Clinical characteristics were evaluated using Fisher’s exact, Chi-Square tests, Students’ t test, and Mann Whitney U test where appropriate.Results: 807 PJI cases were identified including 36 IA and 771 OA. A higher proportion of IA PJI were CN (N=10, 27%) vs. OA PJI (N=109, 14%, p=0.02). IA PJI patients compared to OA patients presented younger (p<0.001), with a higher Charlson Comorbidity Index (p=0.002), had more frequent use of glucocorticoids (p<0.001) and a larger proportion were female (p<0.001). Of 88 PJIs reviewed for histopathology, within the IA cohort, a higher proportion of CP-IA had >10 PMN per HPF (p= 0.003) and met MSIS criteria (p=0.009) but presented with less chronic inflammation (p=0.017).Conclusions: This hypothesis-generating study suggests that culture negative PJI is more frequent in patients with IA than OA. Higher rates of prior PJI, differences in histopathology, and better clinical outcomes suggest biologic differences between CN and CP PJI that should be explored further in a prospective study.