The metacarpophalangeal joint (MCP) is the joint between your fingers and palm. Injury to these joints can cause impaired function of your fingers. The most common, long term ailment of these joints is due to Rheumatoid Arthritis. In severe Rheumatoid Arthritis, the hands have extremely limited function due to stiffness, pain, and ulnar drift. Ulnar drift is when the swelling of the MCP joints cause the fingers to point toward the small finger side of the hand.