Shoulder Joint

• This ball-and-socket articulation allows for free movement in all planes.

• Your 4 rotator cuff muscles act dynamically to keep this ball in its socket.

• The "ball" in this frontal view of the right shoulder is the head of the humerus, or upper arm bone. This fits neatly into the glenoid fossa, or "socket" of the shoulder joint which is a part of the scapula, or shoulder blade.