Metacarpal bones
The five long bones of each hand’s palm connect the carpal bones at the wrist to the phalanges of the fingers and thumb.
Carpometacarpal joints: Joints between the distal carpal bones and the bases of the metacarpal bones. These joints anchor each metacarpal to the wrist, with mobility varying especially at the thumb.
Thumb opposition: A thumb movement that brings its tip across the palm toward the fingertips. Movement of the first metacarpal at its saddle-shaped base enables the thumb to oppose the fingers.
Boxer's fracture: A fracture of the neck of the fifth metacarpal, often caused by striking a hard object. It is a common injury to the metacarpals, with characteristic angulation at the little-finger knuckle.
Metatarsal bones: The five long bones of the foot that connect the tarsal bones to the toe phalanges. They occupy the foot’s mid-region, paralleling the metacarpals in the palm.
Metacarpophalangeal joints: Joints between the metacarpal heads and the proximal phalanges, forming the knuckles. Each metacarpal head forms the base joint of a finger or thumb.
Opponens pollicis: A thenar muscle that draws the first metacarpal across the palm and rotates it inward. It produces the metacarpal rotation central to thumb opposition.
Bennett fracture: An intra-articular fracture at the base of the first metacarpal, usually involving thumb carpometacarpal instability. This thumb-base fracture shows how a metacarpal injury can disrupt a highly mobile joint.
Phalanges: The bones forming the digits of the hands and feet. Unlike metacarpals, phalanges make up the fingers and toes beyond the palm and sole.
Phalanges of the hand: The bones of the fingers and thumb, arranged in proximal, middle, and distal segments. They continue each metacarpal into the digits, except that the thumb has two phalanges.
Interosseous muscles of the hand: Intrinsic hand muscles between the metacarpals that abduct or adduct the fingers and assist flexion. They arise around the metacarpals and control finger motion relative to the hand’s axis.