The shoulder joint (glenohumeral joint), which allows the loose, free movement of the upper limb, has the widest range of motion among the joints. It is a synovial ball and socket joint, formed by the head of the humerus and the glenoid cavity of the scapula which connecting with a thin cartilage ring. Due to the very loose joint capsule that gives a limited interface of the humerus and scapula, it is the most mobile joint of the human body.
The movement and stability of the shoulder joint are maintained by the surrounding muscles, mostly the rotator cuff. This group of four muscles and their tendons cover and stabilize the joint. Due to the overload of the muscles, the balance of the muscles disbands, which leads to shoulder pain.