A jammed finger is most commonly caused by an injury to the joint in the middle of the finger, where it bends in half. This joint is called the proximal interphalangeal joint (PIP).

Metacarpophalangeal joint (MCP): Also called the knuckle, this is where the proximal phalanx in each finger meets an adjacent hand bone (metacarpal bones).; Proximal interphalangeal joint (PIP ...