The upper limb has one bone in the arm, two in the forearm and 27 in the wrist and hand. This design lets the hand rotate and perform fine movements.
The humerus
The arm bone runs from the shoulder to the elbow. The radial nerve winds around its shaft, so a midshaft fracture can cause wrist drop.
Radius and ulna
The ulna forms the hinge of the elbow, and the radius rotates around it to turn the palm up and down. The radius is on the thumb side and widens at the wrist.
Wrist and hand
Eight carpal bones form the wrist, five metacarpals form the palm and 14 phalanges form the fingers. The scaphoid, at the base of the thumb, is the carpal bone most often broken.
Common fractures
A fall on an outstretched hand can break the distal radius, the scaphoid or the radial head. A punch can break the neck of the fifth metacarpal (boxer's fracture).
At the bedside
Tenderness in the anatomical snuffbox suggests a scaphoid fracture even when the first X-ray is normal, so splint and re-image. After any arm fracture, check the radial pulse and the radial, median and ulnar nerves.
Related guides
Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).