Joint · Hand

Proximal interphalangeal joints (hand)

The middle joint of each finger, between the first and second bones — the one that does most of the visible bending when you close your hand. It is built like the fingertip joint but larger and better restrained: a two-lobed head sitting in a matching groove, strong collateral ligaments either side, and a palmar plate underneath whose proximal edge carries two extra bands running back onto the first bone. Because those restraints stay taut in almost every position, this joint has less slack than any other in the hand. On its back runs the central slip of the extensor hood, and on its floor the two long flexor tendons pass one through the other — an unusual amount of hardware crossing one small joint.