"Separation" of the acromioclavicular (AC) joint, where the end of the collarbone meets the shoulder blade, is actually a sprain of the ligaments that connect the two bones. "Separation" is an old medical term that has been applied to the widening of the space between the bones. Since this problem involves ligaments, it really should be called a sprain.

AC separation is typically an injury of young, active people who fall on the shoulder. Most commonly, it occurs when a person lands on the point...