Knee Osteotomy Decreases Joint Inflammation Based on Synovial Histology and Synovial Fluid Analysis

Purpose To examine the biological changes in the joints of patients with knee osteoarthritis (OA) before and after around‐knee osteotomy (AKO), focusing on synovial fluid (SF) and synovial pathological changes. Methods Patients who underwent AKO for medial compartment knee OA between 2019 and 2021 were examined. SF and synovium were obtained at the time of AKO and plate removal after bone union (mean, 16.8 months range: 11–38 months postoperatively). SF volume and interleukin (IL)‐6 concentrations in SF were assayed using enzyme‐linked immunosorbent assay. Synovitis was assessed histologically using a semiquantitative scoring system. Macrophage infiltration was assessed by immunohistochemistry using a semiquantitative score for F4/80 expression. The M1/M2 ratio was calculated using percentage of cells positive for CD80 and CD163. The expression of proinflammatory cytokines was assessed by the percentage of IL‐1β‐ and IL‐6‐positive cells. The number of vascular endothelial growth factor‐positive luminal structures was counted to assess angiogenesis. The change in each parameter was compared before and after AKO using the Wilcoxon matched‐pairs signed‐rank test. Results Twenty‐four knees of 21 patients were included. SF volume and IL‐6 concentration significantly decreased postoperatively (12.6 ± 2.1 mL vs 4.2 ± 0.6 mL; P < .0001 and 50.5 ± 8.6 pg/mL vs 20.7 ± 3.8 pg/mL; P = .0001, respectively). A significant reduction in synovitis score ( P = .0001), macrophage infiltration ( P < .0003), M1/M2 ratio ( P < .0007), angiogenesis ( P < .0001), and the percentage of IL‐1β‐ and IL‐6‐positive cells in the intima ( P < .008 and P < .002, respectively) was found after AKO. Conclusions SF volume and IL‐6 concentrations in the SF decreased and inflammatory synovium pathology improved after AKO. In addition to biomechanical changes, the biological environment of the joint can be improved after AKO. Level of Evidence Level IV, retrospective therapeutic case series.