In a joint affected by RA, inflammatory cells of the immune system gather in the lining of the joint (called synovium), forming a fibrous layer of abnormal tissue (called pannus). The pannus releases substances that quicken bone erosion, cartilage destruction and damage to the surrounding ligaments. The involved joints lose their shape and alignment, resulting in deformities. Severe deformities lead to loss of joint function and the need for joint replacement surgery.

Risk factors for the development of deformities include high levels of C-reactive protein (CRP), a marker of inflammation in the body, and rheumatoid factor (RF), an antibody (a special protein made by the immune system) present in the blood of many people with RA.
Common Joint Deformities in RA

Boutonniere deformity: The middle finger joint bends toward the palm while the outer finger joint may bend opposite the palm.

Swan-neck deformity: The base of the finger and the outermost joint bend, while the middle joint straightens.

Hitchhiker’s thumb: The thumb flexes at the metacarpophalangeal joint and hyperextends at the interphalangeal joint below your thumb nail. It is also called Z-shaped deformity of the thumb.

Claw toe deformity: The toes are either bent upward from the joints at the ball of the foot, downward at the middle joints, or downward at the top toe joints and curl under the foot.

Treating Joint Deformities in RA
Once deformities occur, treatments include exercise and splinting. For patients with severe hand disease, an occupational therapist can design an exercise program, as well as splints, to improve function and often slow the progression of deformity. To stabilize finger deformities, specially designed rings can be used as finger splints. To correct more severe finger deformities, finger joint replacement surgery may be necessary. Replacing damaged finger joints with artificial ones does not cure RA, but recovers functionality of the joint.

When RA affects the feet, the toes may become misshapen. If this makes walking or wearing shoes difficult, the deformities may be corrected with surgery or orthotics (such as simple cushioned insoles or custom-made cast devices). However, surgery is no longer common in people with RA, because available therapies work quite well. In many cases, it is now possible to prevent deformities by using disease-modifying antirheumatic drugs (DMARDs) and biologic drugs before the loss of bone (bony erosions) occurs.