The shoulder is a ball-and-socket joint made up of three main bones: the humerus (long arm bone), the clavicle (at the collarbone), and the scapula (also known as the shoulder blade).
The shoulder girdle in its entirety consists of three joints: the shoulder joint proper (glenohumeral joint), the acromioclavicular (AC) joint, and the sternoclavicular (SC) joint. The shoulder joint/glenohumeral joint is the primary joint, where the long arm bone fits into the rounded socket of the scapula. The AC joint is located at the top of the shoulder. It is where the clavicle (collarbone) meets the acromion, a bony projection of the scapula. The SC joint is located in the front of your chest, where the collarbone meets the breastbone (sternum).
The glenohumeral joint is held together by the rotator cuff, which is a group of muscles and tendons that protects the humerus and allows arm movements. Additionally, various other ligaments, muscles, and tendons provide essential stability and movement to the shoulder, ensuring proper function and preventing dislocation.
Injury to any of these components of the shoulder can cause shoulder pain, typically due to overuse, injuries, and repetitive activities. Degenerative diseases may also cause shoulder pain that travels along nerves to the shoulder.