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 a pain arc during active shoulder abduction, while the pain is significantly reduced or even completely absent during passive activities. What is the differential diagnosis of pain arc syndrome? The following is the differential diagnosis of pain arc sign: 1. Shoulder involvement pain: Due to visceral disease, causing shoulder pain, or nociceptive allergy, called involvement pain. The symptoms appear relatively slowly, dull pain, or discomfort, and do not exactly match the direction of the nerve, the area is blurred, and the pain is vague. 2.Limited shoulder joint movement: limited shoulder movement, mostly seen with periarthritis and shoulder joint dislocation. 3.Persistent and severe shoulder pain: Persistent and severe shoulder pain is often caused by shoulder dislocation. There is an obvious history of trauma. It is usually seen in middle-aged people and is typically characterized by a painful arc when the shoulder joint is actively abducted.