Chronic or persistent stage of rheumatoid arthritis
Joints deformities start in this stage after 1 year of rheumatoid arthritis. This stage has periods of activity and inactivity of the disease.
Chronic polyarthritis
In this stage, the disease is gradual and slowly progressing, affecting multiple joints, most commonly the small joints of hands and wrists on both sides of the body. The deformities of the joints start by inflammation and destruction of the synovial membrane, which is a tissue that surrounds the two bone ends and contains fluid to facilitate joint movements. The inflammatory cells in the disintegrated synovial membrane erode and destroy the cartilages at the end of the bone, followed by the destruction of the bone ends. In the end, the immune system forms fibrous tissue that limits and prevents joint movements.
There are common deformities affect joints such as
Swan’s neck deformity
This deformity affects the upper joint of the finger, causing its flexion and a hyperextension of the middle joint of the finger, which gives a swan’s neck appearance to the finger.
Boutonniere deformity
It is the opposite deformity to the swan’s neck, in which the upper joint of the finger is hyper-extended while the middle joint is flexed. These two deformities happened in 4 fingers, and they spare the thumb.
Z deformity
This deformity happens only in the thumb because it has 2 joints only. It is characterized by the upper joint is hyper-extended and the lower joint is flexed.