This article discusses the ligamentous structures of the metacarpophalangeal (MP) joints (see the first image below), proximal interphalangeal (PIP) joints, and distal interphalangeal (DIP) joints. Additionally, the thumb has 2 joints that will be discussed here, the MP joint and the interphalangeal (IP) joint (see the second image below).
Metacarpophalangeal ligaments and interphalangeal ligaments.
The fingers (index through small fingers) are composed of 3 bones each and are all associated with a single metacarpal. Thus, 3 joints per finger exist, all of which have significant motion and require stabilization to prevent subluxation and dislocation. The thumb has 2 bones and a metacarpal for an additional 2 joints. Stabilization is done with a combination of bony restraints, ligaments, and other static soft-tissue stabilizers, and the dynamic action of muscles.
Generally, ligaments are stabilizers of joints. Without them, many of our joints would dislocate or have far too much abnormal motion, leading to degeneration and pain. Providing stability to joints also allows for pressure to be exerted by limbs, fingers, etc, in planes other than the axial plane. Ligaments can be perfectly isometric, meaning they are equally tight throughout the entire arc of motion of a joint, or they can be functionally involved in only a portion of the arc of motion.