Proximal interphalangeal joints of hand

The proximal interphalangeal (PIP) joints of the hand are the articulations between the proximal and middle phalanges of each finger (index through small finger). Each hand has four PIP joints the thumb is excluded, as it has only two phalanges and a single interphalangeal joint.

Anatomy and Structure

The PIP joint is primarily a hinge joint (ginglymus), permitting flexion and extension in the sagittal plane. It has a typical range of motion from 0° extension to approximately 110° of flexion. The joint is a nonconforming articulation: the articular surface of the proximal end of the middle phalanx has lesser curvature than the condyles of the proximal phalanx, creating physiological incongruity that contributes to joint stability and kinematics.

Stabilizing Structures

The PIP joint derives stability from both bony and soft tissue elements:

• Bony contours The bicondylar shape of the proximal phalanx head and the corresponding concavity of the middle phalanx base resist lateral and rotational stress.

• Volar (palmar) plate A strong fibrocartilaginous structure attached to the base of the middle phalanx that limits hyperextension.

• Collateral ligaments The cord collateral and accessory collateral ligaments provide lateral and dorsal stability.

• Extensor apparatus The central slip and lateral bands contribute to dynamic stability and coordinated movement.