1, Overview The subacromial bursa, also known as the subdeltoid bursa, is one of the largest bursae in the body and is located below the acromion, rostroscapular ligament and deep facet fascia of the deltoid muscle. It is located above the rotator cuff and the greater tuberosity of the humerus (Figure 1). When the shoulder is abducted and internally rotated, this bursa slides with the greater tuberosity into the underside of the acromion and cannot be palpated. The subacromial bursa has many protrusions, the most pronounced being the one that extends into the inferior portion of the acromion. In addition, this bursa attaches to the supraspinatus muscle with a small bursal base and a large free edge, which is very beneficial for shoulder motion. Therefore, the subacromial bursa is very important for the movement of the shoulder joint and is known as the second shoulder joint. 2.Etiology It can be caused by direct or indirect trauma, injury or degeneration of supraspinatus tendon, long-term compression and irritation. 3. Symptoms Clinical manifestations: 1. General symptoms Painful motion limitation and limited pressure pain are the main symptoms of subacromial bursitis. The pain is gradually aggravated and is more prominent at night. The pain increases with movement especially during abduction and external rotation (compression of the bursa). 2.Local symptoms There are pressure points in the shoulder joint under the acromion and the greater tuberosity, which can be displaced with the rotation of the humerus. When the bursa is swollen and fluid is accumulated, there is pressure pain in the whole shoulder joint area and the deltoid. To relieve the pain, the patient often puts the shoulder joint in the inversion and internal rotation position to reduce the extrusion and irritation on the bursa. With the thickening and adhesion of the bursa wall, the range of motion of the shoulder joint is gradually reduced to complete loss. Atrophy of the scapular band muscles can be seen in the late stage. 4. Laboratory tests: No relevant laboratory tests. Other auxiliary examinations: X-rays may reveal calcium salt deposits in the supraspinatus muscle. 5. Treatment First, identify the primary cause of health search and apply targeted treatment. Acute treatment includes rest, the administration of anti-inflammatory and analgesic drugs, physical therapy, acupuncture and the affected limb in an abducted and externally rotated position, steroid hormone local injection has a good effect. In the chronic phase, in addition to the above treatments, we should emphasize rehabilitation without increasing pain, mainly to restore the motor function of the shoulder joint in the three axes. If conservative treatment is ineffective, surgical treatment can be considered including bursal resection scraping of calcified foci of supraspinatus tendon, acromion and rostral-shoulder ligament resection and other molding procedures.