Passive axial rotation of the metacarpophalangeal joint.

We measured passive axial rotation at the metacarpophalangeal (MCP) joints of the index, long, ring and small fingers of both hands in 100 healthy subjects using a magnetic position and orientation system called an Isotrak. Large degrees of passive rotation were found, with the ring and small finger MCP joints displaying significantly greater ranges of supination than the other two joints. Supination ranges were also found to be significantly greater than the pronation values in each joint. These results support present anatomical understanding that, during prehensile activities, axial rotation of the MCP joints occurs to allow the hand to adapt to an object being held.