The shoulder girdle contains three anatomical joints where bones meet and two physiological joints created by muscle or ligament attachments to bone. The most familiar of these joints is the glenohumeral joint, a ball-and-socket joint that joins the upper arm to the shoulder.
The acromioclavicular joint joins the lateral end of the collarbone or clavicle to a structure called the anterior acromium atop the shoulder blade. It is a plane joint with limited mobility and serves to transmit forces from the upper arm and shoulder to the skeleton of the trunk. The sternoclavicular joint joins the other end of the collarbone to the sternum or breastbone. It is a saddle joint that functions as a plane joint and is important in thrusting and throwing movements. The scapulocostal, or scapulothoracic, joint is a physiological joint formed by muscles and allows movement of the shoulder blade, or scapula. The suprahumeral joint is formed by the gap between the humerus, or upper arm bone, and the acromion and plays a role in movements of the arm when it is fully flexed at the glenohumeral joint.