This type of damage is termed a fracture. The joint may also become unstable when the surrounding ligaments are damaged. A joint is formed where the bones come together. The bones are held together by tissue called ligaments. The ligaments allow for motion of the boned at the joint, but only within certain ranges of motion.
Sprains occur when the ligaments are stretched more then normal.
This results in a partial tear or complete tear of the ligament. This ligament damage results in the development of abnormal motion at the joint due to the loss of stability. The term sprain merely indicates that a ligament has been damaged. Sprains are divided into several groups depending on the severity of damage to the involved ligament. The ligaments connecting the ankle bones are often over-stretched, and damaged microscopically, but not actually torn.