The metacarpophalangeal joints (MCP) are of the condyloid kind, formed by the reception of the rounded heads of the metacarpal bones into shallow cavities on the proximal ends of the first phalanges, with the exception of that of the thumb, which presents more of the characters of a ginglymoid joint. Arthritis of the MCP is a distinguishing feature of Rheumatoid Arthritis, as opposed to the distal interphalangeal joint in osteoarthritis. [WP,unvetted]. [ http://en.wikipedia.org/wiki/Metacarpophalangeal_joint ]