What parts of the elbow are affected?

The bones of the elbow are the humerus (the upper arm bone), the ulna (the larger bone of the forearm, on the opposite side of the thumb), and the radius (the smaller bone of the forearm on the same side as the thumb).

 The elbow itself is essentially a hinge joint, meaning it bends and straightens like a hinge. But there is a second joint where the end of the radius (the radial head) meets the humerus. This joint is complicated because the radius has to rotate so that you can turn your hand palm up and palm down. At the same time, it has to slide against the end of the humerus as the elbow bends and straightens.

The joint is even more complex because the radius has to slide against the ulna as it rotates the wrist as well. As a result, the end of the radius at the elbow is shaped like a smooth knob with a cup at the end to fit on the end of the humerus. The edges are also smooth where it glides against the ulna.

There are several important ligaments in the elbow. Ligaments are soft tissue structures that connect bones to bones. The ligaments around a joint usually combine together to form a joint capsule. A joint capsule is a watertight sac that surrounds a joint and contains lubricating fluid called synovial fluid.

In the elbow, two of the most important ligaments are the ulnar collateral ligament (UCL) and the lateral collateral ligament. The UCL is also known as the medial collateral ligament. The ulnar collateral ligament is on the medial (the side of the elbow that's next to the body) side of the elbow, and the lateral collateral is on the outside. The ulnar collateral ligament is a thick band of ligamentous tissue that forms a triangular shape along the medial elbow. It has an anterior bundle, posterior bundle, and a thinner, transverse ligament.

Together these two ligaments, the ulnar (or medial) collateral and the lateral collateral, connect the humerus to the ulna and keep it tightly in place as it slides through the groove at the end of the humerus. These ligaments are the main source of stability for the elbow. They can be torn when there is an injury or dislocation of the elbow. If they do not heal correctly the elbow can be too loose or unstable. The ulnar collateral ligament can also be damaged by overuse and repetitive stress, such as the throwing motion.

Valgus Testing of the Elbow