The shoulder joint has always had a courtyard of deep mystery because of its complex anatomy, and even orthopedic surgeons, without specialized training in shoulder surgery, would not dare to enter it. Today, I will be your guide and show you around this big house. Structural diagram of the shoulder joint As the linking hub between the trunk and the upper limbs, the shoulder consists of three bones, the scapula, the humerus, and the clavicle. The scapula is the most complex in shape, with the body, neck, scapular glenoid, scapular gonad, acromion and rostral process; the proximal end of the humerus has a humeral head, major and minor tuberosities, and an inter-nodal groove. A famous French shoulder surgeon, Laurent Lafosse, compared the shoulder joint to a House with a first floor, a second floor, and a basement. The glenohumeral joint, formed by the femoral head and scapular glenoid, is the living room on the first floor, surrounded by the rotator cuff and joint capsule forming the walls, the supraspinatus is the ceiling, the anterior wall is the subscapularis tendon, the posterior wall is the infraspinatus tendon and the small round tendon, and the entire living room is covered with a layer of joint capsule like wallpaper on the articular side of the rotator cuff. The rotator cuff gap is the space between the subscapularis and supraspinatus muscles, which means there are no walls here, only wallpaper, including the superior glenohumeral ligament and rostrohumeral ligament and other capsular ligaments, which are like a curtain that divides the glenohumeral joint and sub rostrohumeral gap into a living room and a foyer. The biceps tendon originates from above the scapular glenoid and leaves the living room like a chimney through the interungual groove and through the ceiling to the foyer. The foyer has an important anatomical landmark, the rostral eminence, which is the attachment point for the pectoralis minor tendon and the union tendon, and is connected to the acromion and clavicle by the rostro-capital ligament and the rostro-clavicular ligament, which reinforce the anterosuperior stability of the shoulder joint. The sub rostral space is located anterior and medial to the glenohumeral joint. This is the foyer on the first floor, in which the rostral process is lateral to the anterior bursa of the subscapularis and medial to the brachial plexus nerve and blood vessels. This is a dangerous area for arthroscopic surgery, which is often referred to as a minefield. However, many experienced surgeons have now entered the danger zone to perform some necessary surgical operations, such as the exposure and release of the brachial plexus nerve. Behind the infraspinatus and teres minor, below the deltoid muscle, there is the last room on the first floor, the subdeltoid space, which is like a stairwell leading upward to the subacromial space on the second floor and downward to the basement containing the axillary nerve. The subacromial space is the second floor, where the supraspinatus and rostro-humeral ligaments become the floor, and the acromion, clavicle and deltoid form the roof. There are two rooms on the second floor, the subacromial bursa is the main bedroom, located below the acromion, and medially, below the clavicle is the suprascapular space, which is the guest bedroom and contains the rostroclavicular ligament, and the suprascapular nerve. Finally, there is the quadrilateral foramen located below the glenohumeral joint, which is the basement and is connected anteriorly to the inferior most part of the sub rostral space and posteriorly to the inferior deltoid space. The quadrilateral foramen is crossed by the axillary nerve, an important nerve that innervates the shoulder muscles. The entire room is reticulated and runs along the anterior part of the subscapularis tendon, successively crossing the deep surface of the subscapularis muscle into the quadrilateral foramen, terminating inside the deltoid and the greater circular muscle. The lower boundary of the quadrilateral foramen, which is also the floor of the basement, is the greater circular muscle and the latissimus dorsi tendon. At this point, the set will take you through the tour. You are not afraid if you are still a little confused, because the home is looked after by a professional shoulder doctor. Some people liken the shoulder doctor to a kitten that starts out timid and only dares to move around in a small basket, but as it grows, it begins to explore the entire kitchen, and once it steps out of the kitchen, the entire house and garden becomes its territory. When you have similar symptoms of shoulder discomfort, do not believe in “prescriptions” or “experience”, but go to a regular hospital and ask a specialist.