Effects of Flexion and Extension on the Collateral and Accessory Ligaments of the MCP Joints of the Fingers.

In extension, the collateral and accessory ligaments are slightly slack and allow abduction and adduction at the MCP joints of the fingers. In flexion, the collateral and accessory ligaments are stretched and allow little abduction and adduction at the MCP joints of the fingers.

(From OatisCA., ed. Structure and function of the bones and joints of the wrist and hand. In: Kinesiology: The Mechanics and Pathomechanics of Human Movement. 2nd ed. Baltimore: Lippincott Williams & Wilkins; 2009:255–293.)