The shoulder is one of the most complex and moveable joints in the body. It is composed of the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone). Working in tandem with these bones are muscles, tendons, and ligaments, which anchor the shoulder in a stable position. When any of these areas are damaged, it can impact the entire joint and limit movability. Because of the complexity of the joint, it is frequently the site of injury. If you are experiencing stiffness, feel as if your shoulder could pop out of the socket, or are lacking strength in the shoulder, it is highly likely that you have an injured shoulder.