The rotator cuff is composed of four sisters: the supraspinatus, infraspinatus, teres minor and subscapularis, which play an important role in the stability and function of the shoulder joint. The supraspinatus is located directly above the humeral head and is mainly responsible for the supination and abduction of the shoulder joint, which is the most important function; the infraspinatus, teres minor and subscapularis are responsible for external rotation and internal rotation. Under normal circumstances, there is enough space in the subacromial space for the contraction of the rotator cuff muscles to drive the humeral head into forward flexion, abduction, internal and external rotation, etc. The rostral arch is at the periphery and the rotator cuff is in the middle, and their centers of rotation merge with the center of rotation of the humeral head. The rotator cuff is a weak point in the rotator cuff. The tendon, which is very elastic when young, degenerates in old age and slowly loses its elasticity, plus the lack of blood supply at the end of the tendon, strain after repeated exercise, or trauma such as pulling or falling can cause it to tear. Sometimes, although the rotator cuff is still good, the osteophytes of the acromion develop bone spurs, which can also cause impingement, leading to acromion impingement syndrome. In some patients, the anterior part of the rotator cuff may become hooked, i.e. hooked rotator, with bone growth and swelling of the synovial membrane. From harmony to impingement, from smoothness to obscurity, the rotator cuff is caught between the rotator cuff and the humeral head, becoming a victim of tough fights, and the already fatigued and damaged rotator cuff tendon fibers are aggravated by repeated impingements, and the fissures become larger and larger, leading to the occurrence of rotator cuff injury. In the long run, the soft rotator cuff in the middle becomes the victim of a fight between the rotator cuff and the humeral head, resulting in rotator cuff injury. However, the patient is often unaware of this. She or he may be a housewife, a teacher, a white-collar worker, a surgeon, or an athlete, and she or he starts to have pain in the shoulder from one day to the next. At first, the pain was only when the arm was raised and abducted, but later it was also painful when sleeping, and no matter how to adjust the sleeping position, the shoulder pain was unbearable and seriously affected the sleep, often waking up late at night with pain and staying alone until morning. …… saw several doctors and was considered to be “frozen shoulder”. After listening to the advice of my neighbors to exercise, I went to practice climbing the wall, practicing pulley, and desperately practicing shoulder supination, but I never thought the situation would get worse. Therefore, acromioclavicular impingement and rotator cuff injury are conditions that are easily missed and overlooked. How to differentiate from frozen shoulder The full name of impingement is subacromial impingement syndrome. It is a condition in which the humeral head and greater tuberosity repeatedly strike the anterior border of the acromion and subacromial structures during shoulder abduction, causing local bone growth, sclerosis, and compression of the subacromial bursa and rotator cuff tissue, resulting in shoulder pain, weakness, and limited movement. Once combined, rotator cuff injuries tend to get progressively worse and do not heal on their own; 50% of patients can heal on their own within a year to a year and a half with conservative treatment. Therefore, if the shoulder pain does not improve for more than 1.5 years, most of the time it is not frozen shoulder but rotator cuff injury and impingement of the rotator cuff. In addition to the course of the disease, there is also a significant difference in the clinical manifestations of the two problems. In acromioclavicular impingement, there is an arc of pain during active abduction of the shoulder, i.e., significant pain can occur within the range of 60° to 120° of shoulder abduction, while the pain decreases during passive activities, and the acromioclavicular impingement test: Neer’s sign and Hawkins’ sign are positive. In combination with rotator cuff injury, there is a decrease in supraspinatus muscle strength, a positive supraspinatus stress test, and pressure points in the greater tuberosity. In contrast, in frozen shoulder, the active and passive movement of the shoulder joint is limited in all directions, especially passive external rotation of the shoulder joint, and the pressure points are often in the anterior aspect of the shoulder joint, lateral to the rostral process. In addition, an x-ray of acromion impingement is a simple and effective diagnostic tool, as it can reveal the acromion bones and the narrow gap between the acromion and the humeral head, while an MRI plain scan can directly and clearly show signs such as rotator cuff tendon tears and loss of the surrounding fatty band to help confirm the diagnosis. Imaging of frozen shoulder is often unremarkable. Arthrography can be helpful in the imaging diagnosis of frozen shoulder, often showing a significant reduction in the volume of the joint capsule. Rotator cuff injuries should be treated aggressively, but delayed treatment can be disabling. Rotator cuff injuries require early diagnosis and treatment. The purpose is to eliminate edema and congestion and to relieve local pain. Physical therapy, exercise modification, non-steroidal anti-inflammatory drugs and local closure therapy can be applied. These exercises are likely to cause repeated impingement of the humeral head and the acromion, aggravating the condition. If conservative treatment fails to improve shoulder discomfort, early hospitalization for arthroscopic subacromial decompression should be performed to avoid the development or aggravation of rotator cuff injury. Moderate to severe rotator cuff injuries or partial rotator cuff tears that do not resolve over a long period of time can lead to muscle atrophy, shoulder stiffness, and long-term pain that can also lead to depression and neurological deficits. An arthroscopic minimally invasive rotator cuff repair is required as soon as possible. The torn rotator cuff will be re-fixed to the bone surface in order to allow the rotator cuff to heal. After the surgery and then systematic rehabilitation, the patient can mostly recover the function. Otherwise, once a huge irreparable rotator cuff tear is formed, it can lead to disability of the affected limb, osteoarthritis of the shoulder joint, and many patients can only eventually receive artificial joint replacement to relieve their condition. To sum up, if you are over 40 years old, or if you have shoulder pain after repeatedly engaging in over-the-top sports or trauma, especially if the pain is aggravated by raising your hand over your head, accompanied by a feeling of weakness, you should first suspect rotator cuff injury and seek medical attention from a sports injury specialist as soon as possible.