No evidence of SARS-CoV-2 in the knee joint: A cadaver study

Grassi, M.; Giorgi, V.; Nebuloni, M.; Zerbi, P.; Gismondo, M. R.; Salaffi, F.; Sarzi-Puttini, P.; Rimoldi, S. G.; Manzotti, A.

Background: Despite the considerable research efforts being made to learn more about COVID-19, little is known about the presence of SARS-CoV-2 genetic material in biological fluids other than respiratory droplets, blood, and feces 1,2. In particular, little is known about the presence of SARS-CoV-2 in the joints either post mortem 3 or in vivo 4. To the best of our knowledge, only Lopéz-Gonzalez et al.5 have published a description of acute arthritides occurring during hospitalisation due to COVID-19, and they did not find any SARS-CoV-2 genetic material in the patients' synovial fluid samples. Objectives: The aim of this post mortem study was to assess the presence of SARS-CoV-2 RNA in the knee synovial fluid, synovial tissue, and bone tissue of COVID-19 patients in order to discover whether the joint is a possible route of transmission during orthopaedic surgical procedures, and clarify the possible role of SARS-CoV-2 as a directly arthritogenic virus. Methods: Post mortem synovial fluid, synovial tissue and bone tissue samples were collected from the knees of five patients who died of COVID-19 in our hospital between September and October 2020, and analysed for the presence of SARS-CoV-2 using a commercial real-time polymerase chain reaction (RT-PCR) panel. Quantitative RT-PCR was used to test post mortem nasopharyngeal swabs of all of the patients. Results: No SARS-CoV-2 RNA was detected in any of the knee samples, despite the positivity of the throat swab. Conclusion: Our findings indicate that SARS-CoV-2 was not detected in knee synovial fluid, synovial membrane or bone. Therefore, our results suggest that all healthcare professionals performing surgical procedures on the joints of COVID-19 patients are exposed to a risk of contagion due to exposure to respiratory droplets, blood and body fluids, but not to direct exposure to joint-or bone-related tissues. Furthermore, given that some case reports of arthritis in COVID-19 patients 5-8 show that it is possible that COVID-19 patients display viral-mediated arthralgias and arthritis, the absence of the virus in the knee highlighted by our study suggests that it is unlikely that SARS-CoV-2 has a direct inflammatory action on the joint, but it could induce an inflammation-related reaction, manifesting as a reactive arthritis 9.