CorpusHuman Anatomy
SkeletalBone group

Metacarpals

Ossa metacarpi

Also known as: metacarpal bones, knuckles

Five miniature long bones forming the skeleton of the palm, numbered I (thumb) to V (little finger). Their heads form the knuckles.

Show on body map

Overview

Each metacarpal has a proximal base (articulating with the distal carpal row and adjacent metacarpal bases), a shaft (slightly concave anteriorly) and a distal rounded head that articulates with the proximal phalanx at the metacarpophalangeal (MCP) joint and forms a knuckle when the fist is clenched. The 1st metacarpal is the shortest and stoutest and is the most mobile, with a saddle joint at its base and a flexion–rotation that orients the thumb pad toward the fingers. The 2nd is the longest and its base is grooved to lock with the trapezoid; the 2nd and 3rd form a rigid central unit, while the 4th and 5th have mobile CMC joints that allow cupping of the palm. The 3rd metacarpal has a styloid process at its base (extensor carpi radialis brevis).

The interosseous muscles arise from the shafts; extensor and flexor carpi tendons insert on the bases (extensor carpi radialis longus — 2nd, brevis — 3rd, ulnaris — 5th; flexor carpi radialis — 2nd/3rd).

Location

Palm of the hand, between the carpus and the proximal phalanges.

Parts & subdivisions

  1. Base
    Articulates with the distal carpal row (CMC joints).
  2. Shaft
    Origin of the palmar and dorsal interossei.
  3. Head
    Forms the knuckle; MCP joint with the proximal phalanx.
  4. 1st metacarpal
    Shortest, thickest, most mobile; saddle joint with the trapezium.

Anatomy

Articulations

Carpometacarpal joints (distal carpal row), intermetacarpal joints (bases), metacarpophalangeal joints (proximal phalanges).

Ossification

Primary centre in each shaft ≈week 9; secondary centres in the heads of metacarpals 2–5 but at the base of the 1st metacarpal (like a phalanx), appearing ≈2–3 years and fusing ≈15–19 years.

Function

  • Form the framework of the palm
  • Allow cupping of the hand and opposition of the thumb
  • Attachment for interossei, thenar/hypothenar and wrist muscles

Clinical significance

Boxer’s fracture

Fracture of the neck of the 5th metacarpal after punching a hard object; the head angulates volarly (loss of the knuckle). Check for rotational malalignment (scissoring) and "fight bite" wounds.

Bennett and Rolando fractures

Intra-articular fractures of the base of the 1st metacarpal: Bennett is a two-part fracture–subluxation (abductor pollicis longus pulls the shaft proximally); Rolando is comminuted (Y- or T-shaped). Both are unstable.

Compiled from standard anatomy and physiology references — see the Skeletal System sources. For education only; not medical advice.