The arm will not be dislocated naturally, dislocation occurs, most of the cases are due to external injury, but if there is a habitual dislocation of the joint, it is possible that the entire external injury force is not particularly large, or even in the slight pulling force can be caused by dislocation of the joint. And there will be some pain after the dislocation, the range of motion is limited, and there is a clear sense of emptiness when touching the joint area. If there is a slight pulling action injury, without the symptoms described above is not necessarily a dislocation of the joint, it may be a simple muscle pulling injury, so you should go to the hospital to do a radiographic examination, to clarify whether there is a dislocation of the situation exists. If the joint has been dislocated before, you should pay attention to protect it as much as possible to avoid dislocating the joint again and forming habitual injury.