If you've dislocated a joint, you can usually tell by looking at the joint that it's not right. The joint will look deformed compared to the same joint on the opposite side. You may see an indention or a bulge near or in the socket. You will have severe pain and will not be able to move that part of the shoulder, arm, or leg.
In many cases, the force of the injury stretches or tears the ligaments that hold the bone inside the joint and the bone is no longer seated properly in the joint.