Anatomy of the proximal interphalangeal joint.

The proximal interphalangeal joints (PIPs) of the fingers are crucial for normal digital and hand function. Studies of their anatomy reveal subtle bony differences that dictate the precise planes of motion allowed in the constrained joint. Soft tissue restraints guide the cartilaginous surfaces through permissible ranges of motion. Understanding these restraints and the precise orientation of other joint structures assists treatment of conditions affecting the PIP joint.