Knee Alignment Correction by High Tibial Osteotomy Reduces Symptoms and Synovial Inflammation in Knee Osteoarthritis Accompanied by Macrophage Phenotypic Change From M1 to M2

This study aimed to determine whether alignment correction by high tibial osteotomy (HTO) can change the biologic intraarticular microenvironment of osteoarthritic (OA) knees.Synovial tissue (ST) and fluid (SF) were collected from the affected knees of 31 OA patients during initial HTO and plate removal surgeries. Changes in gene expression in ST were investigated by microarray and real-time polymerase chain reaction (PCR). ST specimens were also evaluated histologically using synovitis scores and immunofluorescence staining to determine macrophage polarity. Cytokines and chemokines in SF were analyzed by enzyme-linked immunosorbent assays. The mechanism of macrophage polarization was investigated in human peripheral blood mononuclear cell-derived macrophages and fibroblast-like synoviocytes (FLS) stimulated with cartilage fragments. We also evaluated Spearman correlations between Knee Injury and Osteoarthritis Outcome scores (KOOS) and macrophage-related gene expression.The microarray results indicated down-regulated inflammatory genes and pathways. Real-time PCR determined that genes expressing proinflammatory IL1B and IL6 were down-regulated and M2 macrophage-related IL1RA, IL10, CCL18, and CD206 were up-regulated. Histologic findings revealed attenuated synovitis scores and a shift from M1 to M2 macrophages. Interleukin-1β (IL-1β) concentrations in SF decreased after HTO. Cartilage fragments were responsible for M1 macrophage polarization and proinflammatory gene and protein expression in macrophages, whereas cartilage fragments up-regulated only IL-6 protein in FLS. Postoperative KOOS positively correlated with the expression of the M2-related genes CCL18 and CD206.Correction of lower limb alignment with HTO attenuated synovial inflammation and changed macrophage polarization from M1 to M2, suggesting an improved intraarticular environment in knee OA.