Shoulder. Coloured X-ray of a healthy shoulder joint. The joint is a ball-and-socket joint, with the ball (lower right) of the upper arm bone (humerus) fitting into the socket (centre left) of the shoulder blade (scapula). Above these, at upper left, is part of the collarbone (clavicle), which supports the arm. This joint allows rotation and movement in any direction, unlike the hinge joints of the knees and elbows.