The primary protein that makes up bone, collagen, has a higher tensile strength than steel, but it also has a flexibility that allows it to absorb tremendous pressure. A mineral, calcium phosphate, helps create hard bone. Because of this, bones are both strong and flexible.

This is important for the large bones in the arm as it is human instinct to throw our arms in front of us during moments of panic, whether it be a car accident or simply bumping into a wall.

The large bones of the arm include:

  • Humerus: This bone runs down from the shoulder socket and joins the radius and ulna at the elbow.
  • Radius: A forearm bone, it runs from the elbow to the thumb side of the wrist.
  • Ulna: This forearm bone runs from the elbow to the “pinkie” side of the wrist.

These three bones join to form the elbow. The elbow actually forms three different positions when the heads of the three bones vary slightly. These movements are so small that the untrained eye rarely notices the changes in position.

The ends of the radius and ulna join bones at the hand to form the wrist, which is formally known as the carpus. Together with the bones in the palm of the hand, these bones form three rows. The bones of the wrist are:

  • Scaphoid
  • Lunate
  • Triquetrum
  • Trapezium
  • Trapezoid
  • Capitate
  • Hamate

Including those of the wrist and palm, the hand has 27 bones. Each finger has three series of bones:

  • Proximal phalanges: The largest of the three, these extend directly from the palm. These are where rings rest.
  • Intermediate phalanges: These are situated between the two joints of the fingers.
  • Distal phalanges: These are your fingertips.

Bone fractures are among the most common short-term injuries of the arm. These typically occur during high-impact collisions such as automobile accidents, falls, and sports injuries. A fracture to one of the bones in the wrist is one of the most common bone breaks.

The radius and ulna — the bones of the forearm — are also commonly broken bones. They are often healed with casts to immobilize the bone, but compound fractures (multiple breaks) may require the surgical implantation of pins and other types of reinforcement.