What causes ankylosis in severe rheumatoid arthritis?

In severe rheumatoid arthritis, ankylosis—the firm union and immobilization of a joint—is primarily caused by the progressive destruction of articular cartilage due to chronic inflammation.12

As the disease advances, the synovial membranes thicken and produce a layer of granulation tissue known as pannus. This tissue protrudes over the cartilage, leading to its erosion and destruction. When the injury is severe, large areas of bone are denuded of cartilage, causing adhesions to form between the articular surfaces.21

These adhesions subsequently transform into mature fibrous or bony connective tissue, creating a firm union between the bony surfaces. Additionally, the joint may become fixed in place by the thick, hardened pannus itself. This process interferes with joint motion and can result in total immobility, particularly in the absence of proper physical therapy.12