The hand contains more than 25 joints, and these joints are particularly susceptible to inflammation for people with rheumatoid arthritis (RA). In fact, inflammation, swelling, and stiffness in the knuckles and wrists can be the first signs of this chronic systemic autoimmune disease.
Painful symptoms appear when the immune system mistakenly attacks the joints of the hand. Simple tasks such as opening a jar or turning a key can become difficult.
Hand Joints Affected By RA
The disease often appears in one or more of the following joints in the hand:
- The metacarpophalangeal (MCP) joints, or large knuckles, where the fingers and thumb meet the hand
- The proximal interphalangeal (PIP) joints, or middle knuckles
- The joints of the wrist that connect the wrist’s eight carpal bones with each other and the bones of the forearm (the radius and ulna); these joints include the carpometacarpal joint, midcarpal joint, radiocarpal joint, and intercarpal joints
The distal interphalangeal (DIP) joints, or the outermost joint of the fingers and thumb, are affected by rheumatoid arthritis less frequently. When DIP joints are affected, it is typically only after symptoms appear in the MCP or PIP joints. It is more common for DIP joints to be affected by osteoarthritis than by RA.
How Rheumatoid Arthritis Causes Hand Pain
Like many joints in the body, the joints in the hand are synovial joints. These joints are flexible and surrounded by a thin, pliable membrane called synovium. The synovium produces synovial fluid, a thin, clear, viscous substance that normally nourishes and lubricates the joint, enabling movement.
In people who have rheumatoid arthritis, however, the joints of the hand can become inflamed when the body’s immune system malfunctions and attacks healthy tissue in the fingers and wrists.
- The immune system sends white blood cells, called leukocytes, to invade one or more hand joints.
- The white blood cells trigger inflammation in the hand joints’ synovium. When synovium is inflamed it is called synovitis.
- The inflamed synovial tissue may continue to react to the white blood cell invasion by adding layers of new synovial cells at a very rapid pace. This new, abnormal tissue is called pannus.
- The rheumatoid pannus tissue squeezes into the joint space between bones and releases proteins that degrade the hand joints’ articular cartilage and bone.
- The pannus may create excess fluid that contributes to wrist and knuckle swelling.
The biochemical changes in the joint capsules of the hand cause inflammation that can be seen and felt. Changes can also occur in parts of the hand and wrist, including the tendons.
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Tenosynovitis in the Hands
In addition to encapsulating joints, synovial tissue surrounds most tendons, structures that connect muscles to bones. Rheumatoid arthritis can cause a tendon’s synovial sheath to become inflamed, a condition called tenosynovitis. The inflammation is not always painful but can lead to tendon damage.
Tenosynovitis of flexor tendons in the hand is called trigger finger. Flexor tendons in the hand allow a person to bend his or her fingers, such as when making a fist. When a flexor tendon is inflamed it can cause “triggering” of that finger—the PIP joint gets stuck in a bent position, as if pulling the trigger of a gun.
At least one study suggests that tenosynovitis of flexor tendons is a strong predictor of rheumatoid arthritis.1
Over time, damage to joints, tendons, and ligaments (which connect bone to bone) can cause bones to become malaligned, resulting in hand deformities.