Along with a grinding feeling, you may also feel like your shoulder locks into place at times. This is a result of the function of the labrum, which is to keep the bones in their proper place. Typically, the humerus and scapula can move freely past each other because the labrum provides a buffer between the two bones.
When you suffer from a labrum tear, the bones are directly in contact with each other and this could cause them to get stuck. If your bones get stuck on each other you may feel like your shoulder is locked in place. If this happens you should not force your shoulder to move as you can cause even more damage.
Go to the emergency room right away so that a doctor can look over your injury. You will likely have the shoulder immobilized so that the bones do not cause more damage to each other.