The elbow, in essence, is a joint formed by the union of three major bones supported by ligaments. Connected to the bones by tendons, muscles move those bones in several ways.

The bones that create the elbow are:

  • Humerus: This long bone extends from the shoulder socket and joins the radius and ulna to form the elbow.
  • Radius: This forearm bone 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.

The elbow can move in three ways based on slight variations in the positions of the heads of the three bones. The first is the large hinge action that is used in most movements of the arms, such as holding bags of groceries or doing bicep curls. The other movements are so small that the untrained eye rarely notices the changes in position, but they are important for motor function of the hand and wrist. Inside and outside the elbow joint, there are points where tendons attach. These tendons allow for wrist and hand movements. For example, they allow the hand to rotate.  The elbow bones are held together primarily by fibrous tissue known as ligaments. The ulnar collateral ligament, or UCL, on the inner side of the joint closest to the body is the primary stabilizer. This thick triangle-shaped band connects the head of the humerus to the heads of the ulna and radius.

The UCL can be torn or completely ruptured, which would cause severe pain on the inside of the elbow, a popping noise, swelling, and bruising. Injuries to the UCL are common among baseball pitchers, football quarterbacks, ice hockey players, and racquet sport players due to the type of motion these sports involve.

The other ligament in the elbow is the radial collateral ligament. Located on the outside of the elbow, it prevents excessive extension of the elbow.

Bone fractures are among the most common short-term injuries of the elbow as it is a common point of contact during high-impact collisions such as automobile accidents, falls, and sport injuries.

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

Another common fracture occurs at the heads of the ulna, radius, and humerus at the elbow. Although a break here is not always a complete fracture, it can cause swelling and extreme pain.