What is the ulnar collateral ligament of the elbow? What does it do?

The ulnar collateral ligament (UCL) is the strongest and stiffest ligament crossing the elbow joint. It is located on the inside edge of the elbow.

Ligaments connect one bone to another. They are designed to keep the two bones from moving too far in one or more directions. Connecting the upper arm bone (humerus) to the inside bone of the forearm (ulna), the UCL is the main ligament protecting the elbow from angling too far out to the side.