Topic Overview

Metacarpal Bones

General Features

• Five miniature long bones forming the skeleton of the palm.

• Numbered I to V (thumb to little finger).

• Each has:

  • Base (proximal end) → articulates with carpal bones.

  • Shaft → slightly curved, dorsal surface convex.

  • Head (distal end) → rounded, forms knuckles, articulates with phalanges.

Special Notes

• First metacarpal

  • Short, stout, more mobile.

  • Base is saddle-shaped → articulates with trapezium (carpometacarpal joint of thumb).

  • Responsible for opposability of thumb.

• Second metacarpal → largest.

• Third metacarpal → has styloid process on its base.

• Fifth metacarpal → base has facet for hamate.

Clinical Anatomy of Metacarpals

• Fractures

  • Boxer’s fracture → fracture of neck of 5th metacarpal (from punching injury).

  • Bennett’s fracture → fracture dislocation at base of 1st metacarpal (thumb), involves carpometacarpal joint.

  • Rolando’s fracture → comminuted intra-articular fracture at base of 1st metacarpal.

• Knuckle prominence → formed by heads of metacarpals, useful in surface anatomy.

• Congenital anomalies → shortening of 4th and 5th metacarpals in pseudohypoparathyroidism (Albright’s hereditary osteodystrophy).

Ossification of Metacarpals

• Each metacarpal ossifies from two centers (shaft and head/base).

• Primary center: shaft, appears in 9th week intrauterine life.

• Secondary centers:

  • For head in metacarpals II–V.

  • For base in metacarpal I (thumb).

• Time of appearance → around 2 years of age.

• Fusion with shaft → between 15–18 years.

• Thus, metacarpals have 2 centers each (except 1st, where secondary center is in base).