• C Montoya-delaTorre, J A Fernández-Valencia, J C Martínez-Pastor, L Morata, A Soriano, and E Muñoz-Mahamud.
• Department of Orthopedic Surgery and Traumatology, Hospital Clinic, University of Barcelona, Barcelona, Spain. caromontoyadelatorre@gmail.com.
• Arch Orthop Trauma Surg. 2021 Mar 25.

IntroductionIt remains unclear whether rheumatoid arthritis might be a cause of false positive of the histology for the diagnosis of prosthetic joint infection. Our aim was to evaluate the usefulness of the histology for the diagnosis of infection during hip and knee prosthesis revision in patients with rheumatoid arthritis.Materials And MethodsAll patients with the diagnosis of rheumatoid arthritis (RA) undergoing hip or knee revision surgery (total or partial) were retrospectively reviewed. Positive histology was considered when ≥ 5 neutrophils per high-power field (400×) were found in at least five separate microscopic fields. Patients who presented ≥ 2 positive cultures for the same microorganism or the presence of fistula were considered as "true positives".ResultsThirty-two hip (n = 12) and knee (n = 20) revision procedures were performed. Sensitivity, specificity, positive and negative predictive value of the histology were 50%, 78.6%, 25% and 91.7%, respectively. Six out of the eight patients presenting with positive histology had negative cultures (75.0% of false positives).ConclusionsOur results suggest that, in the context of RA, negative histological results have a very high negative predictive value. RA poses false positive histology results for the diagnosis of infection during hip and knee revision when conventional cultures are used for diagnosis of infection.

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