Dislocation of the acromioclavicular joint can occur due to direct violence from the upper part of the shoulder impacting downward on the acromion, or indirect violence causing dislocation by excessive traction on the shoulder joint downward, or the upper limb falling against the chest wall and the end of the shoulder hitting the ground either in front or behind. The force is applied to the end of the shoulder peak, causing the scapula to move forward or downward (or backward) and causing dislocation. In mild cases, only the head of the joint is torn and there is no deformity displacement. In severe cases, the acromioclavicular ligament and rostral ligament are ruptured, and the external end of the clavicle is misaligned downward and inward due to the action of the trapezius muscle, resulting in a deformed displacement of the acromioclavicular joint. There are three types of dislocation: 1. Type 1: Sprain of the acromioclavicular joint capsule and ligaments without exact ligament rupture; acromioclavicular joint dislocation 2. Type 2: Rupture of the acromioclavicular joint capsule and ligaments, and “semi-dislocation” of the lateral end of the clavicle; 3. Type 3: Rupture of the acromioclavicular ligament and rostral ligament, and “true dislocation” of the lateral end of the clavicle. The lateral end of the clavicle is “true dislocation”. Symptoms and signs Dislocation of the acromioclavicular joint is very common. It is mostly seen in young people with sports trauma. In type I, there is mild swelling and pressure pain at the acromioclavicular joint, and neither clinical examination nor radiographs can reveal a “subluxation” or “true dislocation” of the lateral clavicle. In the second type, there are the same signs at the shoulder-clavicular joint, and the lateral end of the clavicle is higher compared with the contralateral side, and there is a feeling of elasticity when pressing hard. In the third type, the lateral end of the clavicle has been raised above the acromion, and the local swelling is heavier than the above two types, and the shoulder joint movement is also affected. Pathophysiology The mechanism of dislocation can be caused by either direct or indirect violence, but direct violence is more common. Excessive violence may also rupture the raphe-clavicular ligament. There is another kind of indirect violence, in which the shoulder and elbow are in 90 degrees of flexion during the fall, when the humeral head is on top of the scapular glenoid and the acromion, and the violence transmitted posteriorly can rupture the acromioclavicular ligament and the raphe-clavicular ligament. Classification It can be divided into three types. 1. Type 1 The shoulder lock joint capsule and ligaments are sprained, and there is no exact ligament rupture. 2.Type 2: Rupture of the acromioclavicular capsule and ligaments, and “subluxation” of the lateral end of the clavicle. 3.Type 3 Rupture of both the acromioclavicular ligament and the raphe-clavicular ligament, and “true dislocation” of the lateral end of the clavicle. Diagnosis Etiology and examination Most often seen in young people with sports injuries. X-ray examination X-ray examination can show a subluxation or true dislocation of the acromioclavicular joint, which must be compared with the contralateral acromioclavicular joint. Treatment options 1.Type 1 No special treatment is necessary, and the patient should be suspended by a triangular scarf for several days. 2.Type 2 There are various opinions. a.Treat as type 1, the reason is that not every type 2 case will produce chronic pain. Once the pain occurs, it is not too late to operate; b. Forced repositioning of the lateral end of the clavicle using pressure pads and slings, which is only used in children; c. Closed repositioning and internal fixation under fluoroscopy: under local anesthesia, an assistant presses the lateral end of the four Gu’s for closed repositioning, and the surgeon inserts a kerfing needle into the medullary cavity of the clavicle via the acromion under fluoroscopic supervision; d. Incisional repositioning and reconstruction of the rostral ligament. 3.Type 3 should be treated surgically, and two surgical methods are more common. a, incisional repositioning with tension band method of fixation; b, additional rostral ligament reconstruction.