Why are joints stiff after waking in rheumatoid arthritis?

In rheumatoid arthritis, joint stiffness—particularly after waking—is primarily a result of inflammation of the synovial membranes, which are the tissues that line the joints and produce lubricating fluid.12

As this chronic connective tissue disease progresses, the synovial membranes become thickened, red, and swollen. This inflammatory process often leads to an increase in synovial fluid and the formation of a layer of granulation tissue known as pannus. Over time, this pannus can erode the cartilage and cause the joints to become fixed in place, a condition known as ankylosis. The stiffness experienced after periods of inactivity, such as sleep, is a clinical manifestation of this ongoing inflammatory activity and the resulting structural changes within the joint capsule.12