The shoulder is the most flexible joint in the b ody making it the most susceptible to instability and injury. It is a ‘ball-and-socket’ joint. A ‘ball’ at the top of the upper arm bone, humerus, fits neatly into a ‘socket’, called the glenoid, which is part of the shoulder blade, scapula. The shoulder joint is made up several bones and soft tissues. It has three bones, the collarbone (clavicle), scapula, and humerus.
Humerus provides attachment to muscles of the upper arm. Scapula is the bone that connects the upper arm bone with the collarbone.