The shoulder joint is the body’s most mobile joint. It can turn in many directions. But, this advantage also makes the shoulder an easy joint to dislocate.A partial dislocation (subluxation) means the head of the upper arm bone (humerus) is partially out of the socket (glenoid). A complete dislocation means it is all the way out of the socket. Both partial and complete dislocation cause pain and unsteadiness in the shoulder.