The elbow is composed of three bones and the muscles, tendons and ligaments that connect them. The three bones are the radius and ulna, which make up the forearm, and the humerus, or upper arm bone. The elbow is used to carry heavy loads and to position the hand in space. These contrasting tasks require the elbow to be both stable and mobile.

The elbow is a hinge joint, the end of the humerus fits into a notch in the ulna. This allows stable flexion and extension of the elbow. The radius attaches to the humerus at a ball and socket joint, allowing rotation of the forearm and making the hand more mobile.

Four groups of muscles provide motion to the elbow. The flexor-pronator group attaches to the inside of the humerus and flexes the wrist and turns the palm of the hand down. The extensor-supinator group attaches to the outside of the humerus. Its function is to extend the wrist and turn the palm of the hand up. The triceps muscle acts to straighten the elbow, while the brachialis and the biceps muscles flex the elbow. Although the biceps is responsible for some elbow flexion, its primary job is to turn the palm of the hand up. It does this by rotating the radius when it contracts.

Mechanism of Injury

The elbow can be injured as a result of trauma, repetitive use, or degeneration that occurs with age. Trauma is a leading cause of injury in the young. Falls on to an outstretched hand, or falls that lead to a sudden twisting injury to the elbow can lead to fractures or dislocations. Repetitive use is a common cause of elbow injury. People whose occupations require repetitive work, such as carpenters, machinists and typists are particularly susceptible. Athletes who play sports that place stress across the elbow, such as baseball, tennis, golf and softball, can develop elbow pain. Finally, normal wear and tear on the joint can accumulate over a lifetime, and lead to tears of the tendons and ligaments without any specific injury.