Metacarpals

Contents

Name of bone

Metacarpals

Location/Articulation

The metacarpals form a transverse arch to which the rigid row of distal carpal bones are fixed. The peripheral metacarpals (those of the thumb and little finger) form the sides of the cup of the palmar gutter, and as they are brought together, they deepen this concavity. The index metacarpal is the most firmly fixed, while the thumb metacarpal articulates with the trapezium and acts independently from the others. The middle metacarpals are tightly united to the carpus by intrinsic interlocking bone elements at their bases. The ring metacarpal forms a transitional element of the semi-independent last metacarpal.

Besides their phalangeal articulations, the metacarpal bones articulate as follows:

  • The first with the trapezium
  • The second with the trapezium, trapezoid, capitate and third metacarpal
  • The third with the capitate and second and fourth metacarpals
  • The fourth with the capitate, hamate, and third and fifth metacarpals
  • The fifth with the hamate and fourth metacarpal.


Figure 1. The five metacarpal bones

Muscle and ligament attachments

Surface anatomy

Each metacarpal consists of a body and two extremities.

Body

The body (corpus; shaft) is prismoid in form and curved, so as to be convex in the longitudinal direction behind, concave in front. It presents three surfaces: medial, lateral, and dorsal.

  • The medial and lateral surfaces are concave, for the attachment of the interosseus muscles, and separated from one another by a prominent anterior ridge.
  • The dorsal surface presents in its distal two thirds a smooth, triangular, flattened area which is covered in by the tendons of the extensor muscles. This surface is bounded by two lines, which commence in small tubercles situated on either side of the digital extremity, and, passing upward, converge and meet some distance above the center of the bone and form a ridge that runs along the rest of the dorsal surface to the carpal extremity. This ridge separates two sloping surfaces for the attachment of the interossei dorsales.

The collateral ligaments of the metacarpophalangeal joints are attached to the tubercles on the digital extremities.

Base

The base, or carpal extremity (basis), is of a cuboidal form, and broader behind than in front. It articulates with the carpus and with the adjoining metacarpal bones. Its dorsal and volar surfaces are rough, for the attachment of ligaments.

Head

The head, or digital extremity (capitulum), presents an oblong surface markedly convex from below backward, less so transversely, and flattened from side to side; it articulates with the proximal phalanx. The head is broader, and extends farther upward, on the volar than on the dorsal aspect, and it is longer in the antero-posterior than in the transverse diameter. On either side of the head is a tubercle for the attachment of the collateral ligament of the metacarpophalangeal joint.

The dorsal surface, broad and flat, supports the tendons of the extensor muscles. The volar surface is grooved in the middle line for the passage of the flexor tendons, and marked on either side by an articular eminence continuous with the terminal articular surface.

Radiography

Physical examination

Embryology

Anomalies

The fourth and fifth metacarpal bones are commonly “blunted,” or shortened, in pseudohypoparathyroidism and pseudopseudohypoparathyroidism. A blunted fourth metacarpal with a normal fifth metacarpal can signify Turner syndrome.

Injuries/Disorders

Attachments:


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