Arthritis of joints involves inflammation of the synovial membrane. Joints become swollen, tender and warm, and stiffness limits their movement. With time, multiple joints are affected (polyarthritis). Most commonly involved are the small joints of the hands, feet and cervical spine, but larger joints like the shoulder and knee can also be involved. Synovitis can lead to tethering of tissue with loss of movement and erosion of the joint surface causing deformity and loss of function. The fibroblast-like synoviocytes (FLS), highly specialized mesenchymal cells found in the synovial membrane, have an active and prominent role in these pathogenic processes of the rheumatic joints.