Tendons are the structures that attach our muscles to our bones. When a muscle shortens, or flexes, it pulls on a tendon. The tendon moves the bone it is attached to, creating movement in our joints. When a tendon ruptures, the result is weakness of the joint that it is meant to move. In some cases, there is enough support provided by other tendons around a joint that the injury does not result in significant loss of strength or function. In other cases, catastrophic weakness may result.