Shoulder joint motion (gleno-humeral articulation) occurs when there is relative movement between the head of the humerus and the glenoid fossa of the scapula. Like all joints, real motion of either bone can occur, and often both bones are moving. The shoulder is described as not only tri-planar, but also tri-axial. Motion at the shoulder can occur in any of the three planes separately allowing for multiple three-dimensional combinations to facilitate complex functions.