A shoulder dislocation occurs when the upper arm bone, or humerus, pops out of the glenoid, which is the socket in the shoulder blade. This injury can happen due to trauma, such as a fall or a sports accident, and can cause severe pain, swelling, and limited movement in the arm. There are two main types of shoulder dislocations: anterior, where the humerus moves forward, and posterior, where it moves backward. Treatment often involves repositioning the bone, followed by rest and rehabilitation exercises to restore strength and mobility in the shoulder joint.