The shoulder joint is the most flexible joint in the body and has a complex anatomy of its components. The shoulder joint is composed of six joints. Because the humeral head is large and spherical, the joint pelvis is shallow and the small shoulder joint only wraps around 1/3 of the humeral head, and the joint capsule is thin and flaccid, the shoulder joint is the largest and most flexible joint in the body in terms of range of motion. It can do forward flexion, back extension, internal retraction, abduction, internal rotation, external rotation, and circular rotation. The specific causes of shoulder pain are the anatomical deconstruction described above. Next, I will summarize the common causes of shoulder joint pain: Acromioclavicular impingement sign: The shoulder joint pain is caused by degenerative changes in the shoulder joint, formation of subacromial bones and bursal hyperplasia, resulting in a smaller gap under the acromion, resulting in rotator cuff compression and impingement when abducting or raising the arm. It can occur at any age, with the majority of middle-aged and elderly people suffering from it. In reality, this type of disease is the most common cause of shoulder joint pain. Generally speaking, this disease is the culprit of daily shoulder pain. Calcific tendonitis: Calcium salts are deposited in the tendon, most commonly in the rotator cuff tendon of the shoulder joint. The cause of calcium salt deposition is not known, but may be related to tendon degeneration, ischemia and hypoxia, and increased local pressure. Pain due to this type of disorder often results in waking up with pain at night. Rostral impingement sign: Due to various reasons: degeneration, osteophytes, congenital anatomical abnormalities that narrow the anatomical gap between the rostral process and the shoulder joint, the rostral process and the shoulder joint will impinged in the abducted internal rotation position, which then leads to pain. Separation of the acromioclavicular joint: Usually the ligaments between the acromioclavicular joint are damaged due to trauma and the acromioclavicular joint becomes dislocated and separated, resulting in impaired movement of the acromioclavicular joint and pain. Shoulder instability: The most common cause of shoulder instability is a history of shoulder dislocation, irregular treatment of shoulder dislocation or lack of cooperation due to mental illness, which can lead to shoulder instability. This type of disorder causes severe shoulder pain and mobility problems. Rotator cuff injury: This is a tear in the rotator cuff tissue surrounding the humeral head and is mainly caused by impingement of the rotator cuff. Prolonged impingement causes degeneration of the rotator cuff, loss of tendon quality, and eventually tears. Glenoid labrum injury: The fibrocartilage disc that deepens the glenoid at the edge of the shoulder glenoid, or the “edge of the shoulder socket”. Tearing of the glenoid labrum can occur when the upper arm lands directly on the ground during a fall, or when the upper arm is struck directly and abnormal motion of the humerus occurs. Repeated impingement of the posterior glenoid labrum by the greater tuberosity and rotator cuff can also cause injury, which is called internal impingement (soft tissue compression) and is commonly seen in athletes with arms in overhead positions such as badminton, baseball, and tennis. It can also occur with forceful lifting and pulling movements and repeated throwing movements. The most common shoulder labral injury is a tear that occurs at the top of the glenoid labrum, extending anteriorly and posteriorly, called a SLAP tear. Biceps long head tendinitis: Inflammatory changes in the tendon sheath due to repetitive physical exertion resulting in wear and tear of the long head of the biceps tendon, causing congestion and edema. It occurs in middle-aged people and is mainly characterized by shoulder pain, but there is no restriction of movement in the direction of external rotation of the shoulder joint. Frozen shoulder: A type of adhesive capsulitis that causes stiffness of the glenohumeral joint and is characterized by pain around the shoulder joint and limitation of movement in all directions. It mainly affects middle-aged and elderly people around the age of 50 and used to be collectively called “frozen shoulder”. Infections of the shoulder joint, such as tuberculosis and various bacterial infections. The pain is specific to this type of condition due to the specific factors of the infection. Shoulder joint pain due to gallbladder disease: Some gallbladder lesions may cause pain radiating from the right subscapular region, which can be mistaken for shoulder joint pain. Shoulder pain due to heart disease: Some heart attack patients may have radiating pain in the left shoulder joint. Osteoarthritis of the shoulder joint: Due to various causes of damage to the shoulder joint cartilage, the glenohumeral joint may experience painful gap narrowing. Rheumatoid immune shoulder diseases: Various systemic rheumatoid immune diseases can develop synovial-like lesions in the shoulder joint, resulting in shoulder joint pain. Shoulder joint pain due to cervical spine lesions: Various cervical spine diseases such as cervical spondylosis, cervical tuberculosis, and cervical spine tumors can cause corresponding shoulder joint pain and upper extremity sensory abnormalities upper extremity weakness. For a patient with shoulder joint pain, it is generally necessary to make a preliminary judgment by careful history taking, routine shoulder joint photos and photos of special positions combined with professional physical examinations (there are dozens of such examinations, and only professionally trained joint surgeons have the expertise in this area), and if necessary, MRI of the shoulder joint must be performed. Do not jump to a conclusion about frozen shoulder. According to domestic and international statistics, the true “frozen shoulder” (previously known as frozen shoulder) accounts for a very small percentage of shoulder pain, and the most common causes of shoulder pain are acromioclavicular impingement and rotator cuff injury.