Synovial mast cells from knee and hip osteoarthritis: histological study and clinical correlations

Purpose: The aim of this study was to investigate the presence of synovial mast cells (MCs) in hip and knee tissue from osteoarthritis (OA) patients and to correlate them with clinical and radiological data. Methods: Synovial tissue was obtained during arthroplasty from 60 patients, 30 with knee OA and 30 with hip OA. Control synovial tissue was obtained from 30 patients without OA, 15 undergoing above-knee amputation and 15 receiving a hip replacement for fracture. Before surgery, the radiographic findings were graded according to the Kellgren-Lawrence system and clinical data including pain (VAS) and functional information (KOOS and HOOS) was collected. The tissue was stained with hematoxylin–eosin and toluidine blue for histochemistry and incubated with CD117 and CD31 antibodies for immunohistochemistry. MC and vessel number and synovitis score were determined in all samples. Results: Mean MC number, synovitis score and vessel number were significantly higher in the OA samples (p < 0.05) than in control tissue. MC number correlated with the synovitis score and disease severity in both patient groups. Conclusions: The prevalence of MCs in synovium from OA patients and their association with synovial inflammation and pain suggest a role for them in OA pathophysiology.