Arc of pain is a chronic shoulder pain syndrome caused by repeated friction and impingement between the structures in the subacromial space and the rostral shoulder arch during shoulder abduction activities. The common clinical feature is that there is an arc of pain during active abduction of the shoulder joint, while the pain is significantly reduced by passive activities or even no pain at all. The main symptom of this disease is shoulder pain, mainly around the acromion, sometimes involving the entire deltoid muscle, and the pain is worse at night. When the upper arm is abducted to 60°~80°, there is obvious pain, and sometimes the shoulder joint can feel stuck by the “object” and cannot be lifted. The pain arc is positive, that is, the pain only occurs in the range of 60° to 120°. If the shoulder joint is passively abducted, the pain arc sign is atypical; 4. In patients with long duration of disease, shoulder joint movement is limited, mainly in abduction, external rotation and posterior extension; 5. X-ray examination Most patients have normal X-ray examination, but in a few severe cases, the X-ray examination shows sclerosis of the greater tuberosity of the humerus, cystic change or formation of bone superfluity, sclerosis of the anterior border of the acromion, formation of bone spurs on the subacromial surface, partial calcification of the supraspinatus tendon at the attachment point of the greater tuberosity, traumatic arthritis of the acromioclavicular joint, displacement of the humeral head, and narrowing of the subacromial space. Shoulder arthrography is not used as a routine test for this disease, but is mainly used to identify whether the rotator cuff is partially torn or completely torn. The indications for shoulder arthrography are: 1) chronic pain in the shoulder over 40 years of age, with no reduction in symptoms after 3 months of conservative treatment and a positive impingement test; 2) sudden and severe weakness and limitation of shoulder movement due to trauma; 3) unstable dislocation of the acromioclavicular joint or shoulder dislocation with shoulder symptoms, over 40 years of age. If the traffic between the acromioclavicular joint and the subacromial bursa is found during the imaging, it is the basis for the diagnosis of complete rotator cuff tear.