The shoulder consists of bone joints, joint capsules, ligaments and muscles that are connected to each other to form the shoulder. 1. Bone joint and joint capsule: the scapula, clavicle and proximal humerus are connected to form the sternoclavicular joint, acromioclavicular joint and acromioclavicular joint respectively. The shoulder joint is also the most typical ball and socket joint, with a large range of motion, and can be used for multi-axis motion and circular motion. Therefore, the shoulder joint is the most flexible joint in the whole body. 2. Ligaments: There are two important ligaments in the shoulder. One is the acromioclavicular ligament and the other is the rostral locking ligament. Through the two ligaments, the acromioclavicular joint can be kept in a normal position. 3. Muscles: The human shoulder muscles are mainly: deltoid, trapezius, supraspinatus, infraspinatus, teres major, teres minor and other muscles. Among them, the deltoid muscle is divided into three bundles: anterior, middle and posterior, which is the most obvious muscle of the shoulder and plays an important role in the width of the shoulder.