Rheumatoid arthritis is a painful, progressive condition that frequently causes significant difficulty with daily activities. Damage occurs as the immune system mistakenly attacks healthy joint tissues throughout the body, eventually affecting joint movement. Rheumatoid arthritis often affects the joints in the fingers and thumb, restricting movement.
The metacarpophalangeal (MCP) joints are the large knuckles at the base of the fingers. Each joint is supported by ligaments and surrounded by a joint capsule. Tendons that straighten the fingers travel along the center of the back of these knuckles to the tips of the fingers. Healthy MCP joints typically bend to approximately 90 degrees, though 60 to 70 degrees is considered functional range of motion. Rheumatoid arthritis makes the ligaments and joint capsule of the MCP joints loosen. The top bone in each joint moves forward and the tendons on the back of the joint slide to the pinkie side of the knuckles. This prevents the tendons from fully straightening the knuckles. As the MCP joints bend, the tendons pull the fingers even farther toward the pinkie side of the hand. The MCP joints can assume a permanent bent, angled position over time. Fine motor skills -- such as writing and using eating utensils -- become difficult because the fingertips cannot touch the thumb and larger objects cannot be cupped by the hand. Soft splints can be worn to hold the MCP joints in a straighter position before the deformity is permanent. Eventually, joint replacement using silicone implants may be required.
Swan-neck deformity is a common result of rheumatoid arthritis in the middle and last joints of the fingers. This deformity causes the middle joint to hyperextend backward, making the finger look like a swan's neck. Finger movement is severely restricted with this deformity. The middle knuckle is unable to bend, preventing the hand from making a fist to hold objects. Swan-neck can be present in one or more fingers. Oval ring splints can be worn to hold the middle knuckle in a straight position to improve function.
Boutonniere deformity is another common result of rheumatoid arthritis in the fingers. This causes the middle joint of the finger to stick in a downward bent position while the last joint hyperextends, meaning it bends back toward the knuckles. Function is usually retained with this deformity because the middle joint can bend to hold objects, although it does not straighten. Boutonniere deformity is more of a cosmetic problem than a functional limitation.
Rheumatoid arthritis in the thumb significantly impacts movement and function. The thumb is needed for pinching, gripping and fine motor skills. Swan-neck or boutonniere deformities can develop in the thumb. Depending on the deformity, the thumb joint can be hyperextended and unable to bend or stuck in a bent position. Oval ring splints can be worn to hold the thumb joint in a straight position to improve fine motor skills. Neoprene or thermoplastic splints can be worn to support the base of the thumb to improve pinch and grip functions.