The large joints in the hand at the base of each finger are known as the metacarpophalangeal (MP, or MCP) joints. They act as complex hinge joints and are important for both power grip and pinch activities.
Arthritis is the wearing away of the cartilage at a joint. Cartilage is the coating layer of tissue on the end of a bone that acts as a shock-absorber. Loss of cartilage can lead to joint destruction and a shift in the finger position towards the small finger side, which is called ulnar drift. When arthritis affects the MP joints, the condition is called MP joint arthritis.
The MP joints are often affected by arthritis either from routine wear and tear, an injury, or medical conditions.
The most common medical condition causing arthritis at the joint is termed rheumatoid arthritis. Rheumatoid arthritis affects the inner coating of the joint, called the synovium, and can result in the loss of the cartilage between the joints. The cause of rheumatoid arthritis is not known.
Other conditions that can cause loss of the cartilage include previous injuries and other medical conditions such as gout, psoriasis, or infection.
Pain is the main problem with arthritis. At first, the pain usually only causes problems when you begin an activity. Once the activity gets underway, the pain eases. But after resting for several minutes the pain and stiffness increase. When the arthritis condition worsens, pain may be felt even at rest. The sensitive joint may feel enlarged and warm to the touch from inflammation.
In rheumatoid arthritis, the fingers often become deformed as the disease progresses. The MCP joints of the fingers may actually begin to point sideways (towards the little finger). This is called ulnar drift. Ulnar drift can cause weakness and pain, making it difficult to use your hand for daily activities.
Both rheumatoid arthritis and osteoarthritis can affect the IP joints of the fingers. The IP joints may begin to flex (bend) or hyperextend (over straighten), causing characteristic finger deformities. Swan neck deformity occurs when the middle finger joint (the PIP joint) becomes loose and hyperextended, while the DIP joint becomes flexed. When the PIP joint flexes and the DIP joint extends, a boutonniere deformity forms.
Procedural options include cortisone injections to the arthritic joint. Regenerative-type injections (such as platelet-rich plasma [PRP] therapy) can theoretically provide longer lasting pain relief and improved function by stimulating the body’s own natural healing response when conventional treatments have failed.