Shoulder instability occurs when the top of the upper arm bone is forced out of the shoulder socket. This can happen as a result of a sudden injury or from overuse. Once a shoulder has dislocated, it is vulnerable to repeat episodes. When the shoulder is loose and slips out of place repeatedly, it is called chronic shoulder instability.
Labral tears can occur from repetitive shoulder motion or when the tissue rim surrounding the socket experiences an injury. Often, throwing athletes or weightlifters experience glenoid labrum tears from repetitive shoulder motion. The labrum wears down over time, which can also cause tears.