Histopathological evaluation of synovial tissue in advanced osteoarthritis: A retrospective study based on total knee arthroplasty specimens

Osteoarthritis (OA) is a chronic disease characterized by pain, swelling, and joint stiffness, affecting all components of the joint and periarticular tissues. This study aimed to evaluate the histomorphological features of synovial tissue obtained during total knee arthroplasty in patients with grade 4 primary OA and to explore the relationship between synovitis scores and associated pathological changes. This retrospective, single-center cohort study included 115 patients who underwent total knee arthroplasty for grade 4 primary OA between 2020 and 2023. Histological evaluations were performed on archived hematoxylin and eosin stained sections. Synovitis scores were calculated using a semiquantitative scoring system that assessed synovial lining hyperplasia, inflammatory infiltrate, and stromal fibrosis. Additional features such as vascularity, edema, multinucleated giant cells, and calcification were also evaluated. Statistical analyses included descriptive statistics, Chi-squared tests, and Spearman correlation. Synovial inflammation was classified as mild in 73 patients (63.5%), moderate in 37 (32.2%), and severe in 5 (4.3%). Fibrosis was the most prominent histological finding, with severe fibrosis observed in 67 patients (58.3%) and moderate fibrosis in 40 patients (34.8%). The mean synovitis score was 4.9. While inflammation was generally mild to moderate, fibrosis and stromal proliferation contributed significantly to the overall score. A significant correlation was found between synovitis score and age (P = .039; ρ = 0.193), as well as with the presence of multinucleated giant cells (P < .001). Synovial fibrosis appears to be a defining feature of advanced-stage OA and may significantly contribute to pain. However, synovial inflammation should also be recognized as a key component in the disease's pathophysiology. Standardized histopathological scoring systems improve the consistency of synovial assessment and can guide future research. Longitudinal studies investigating the progression of both fibrosis and inflammation across OA stages may support the development of targeted therapies.