Tacoma Farms CBD Oil The shoulder is the maximum freely movable joint in our frame. Because of the variety of motion allowed, it is an volatile joint. It is without difficulty injured because the ball of the upper arm slightly fits in the shoulder socket designed to preserve it. For its handiest stability, the shoulder is anchored through ligaments, tendons, and muscle mass. Some shoulder troubles stand up from damage of these tender tissues because of overuse or weakness of the shoulder.