Shoulder pain is common among people of all ages, but the cause of shoulder pain is not clear to most people, or even to more orthopedic surgeons, who use the term “frozen shoulder” to describe it, which often delays treatment. In fact, the most common cause of shoulder pain is acromioclavicular impingement syndrome. In other words, if you or someone close to you has shoulder pain, the first thing you should suspect is “acromioclavicular impingement syndrome”. Definition: A narrowing of the gap between the humeral head and the acromion, rostrocarpal ligament, and rostral process, possibly accompanied by bone spurs and synovial hyperplasia, in the outer upper part of the shoulder. Clinical manifestations: pain, pain during activity, awakening at night; difficulty in identifying a clear site of pain; difficulty in raising the arm over the head. It is more common in young athletes and middle-aged people. The symptoms may be mild at first, with pain on movement. The pain may radiate from the shoulder to the forearm, producing increased pain when lifting or holding objects; athletes may develop pain when throwing or playing tennis. As the pain progresses, nocturnal pain may develop. Strength or range of motion in the upper extremity may be reduced. Inability to put the hands behind the back and make movements to fasten and unfasten buttons. In severe cases loss of motion may cause frozen shoulder. In acute bursitis, there is significant tenderness in the shoulder. There is limited movement and pain in all directions of the shoulder joint. Diagnosis: An experienced physician can basically confirm the diagnosis by relying on symptoms and signs. Sometimes an x-ray or MRI is needed. Treatment: Conservative treatment: Some patients gradually improve and regain function through conservative treatment. This includes: rest and avoidance of supination; oral NSAIDs, physical therapy; local closure and acupuncture and tui-na may also be effective. The physical therapy process takes several weeks to several months. Surgical treatment: When conservative treatment is not effective, surgical treatment is required. The goal of surgical treatment is to remove the impingement and create a space for the humeral head to move freely. Surgical procedure: Arthroscopic subacromial decompression and acromioplasty. It is a minimally invasive procedure that requires 2-3 puncture holes, each of about 5mm, through which subacromial impingement decompression can be accomplished. The surgeon may also treat concomitant conditions such as acromioclavicular arthritis, biceps tendonitis or partial rotator cuff tears in conjunction with the treatment of acromioclavicular impingement. Rehabilitation: A post-operative neck and wrist sling is usually required for temporary support to promote healing. The joint function can be practiced the day after surgery and the sling can be removed within 2 weeks. The exact recovery depends on the condition and the surgical procedure. It usually takes 2-4 months to obtain complete pain relief and to restore range of motion and strength to the shoulder joint.