• Haider Mussawy, Jozef Zustin, Andreas M Luebke, André Strahl, Veit Krenn, Wolfgang Rüther, and Tim Rolvien.
• Division of Orthopaedics, Department of Trauma and Orthopaedic Surgery, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, 20246, Hamburg, Germany.
• Arch Orthop Trauma Surg. 2022 Nov 1; 142 (11): 2991-2997.

IntroductionOsteoarthritis (OA) and rheumatoid arthritis (RA) represent the most common forms of arthritis, which are mainly caused by mechanical and inflammatory components, respectively. Determination of synovial inflammation in synovial biopsies via the histopathological Krenn score may be crucial for correct diagnosis and treatment. Specifically, it remains unclear whether synovitis scores differ among multiple biopsy locations within a single joint.Materials And MethodsEighty synovial samples were taken from four standardized regions of the knee in 20 patients (ten primary OA, ten secondary OA) undergoing total knee arthroplasty (TKA) or total synovectomy. The Krenn synovitis score (grade 0-9) was determined in a blinded manner by two expert pathologists in all biopsies. Next to the inter-rater reliability, we evaluated the agreement of the determined scores among the four biopsy locations within each knee.ResultsThe inter-rater reliability between the two pathologists was very high (Cohen's kappa = 0.712; r = 0.946; ICC = 0.972). The mean synovitis score was significantly higher in knees with secondary than in primary OA (p = 0.026). Importantly, we found clear differences between the scores of the four different biopsy locations within the individual knee joints, with an average deviation of 10.6%. These deviations were comparable in knees with primary and secondary OA (p = 0.64).ConclusionsWhile we confirmed the synovitis score as a reliable and reproducible parameter to assess the histopathological synovitis grade in the knee, the considerable variability within the joint indicates that multiple synovial biopsies from different regions should be obtained to enable reliable results of the synovitis score.© 2021. The Author(s).

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