Nov 1, - The pain is located over the metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints of the index and middle fingers. Nonetheless, it is important to test for signs of median nerve compression. Studies to rule out other causes, such as a measurement of rheumatoid factor (D) would be. Nerve Injuries Carpal metacarpal arthritis is arthritis at the base of the thumb joint. In a normal joint, cartilage covers the ends of each bone providing smooth and.