Acute posterior dislocation of the shoulder joint accounts for 5% of dislocations. It is caused by direct violence to the anterior shoulder joint, indirect violence to the shoulder joint in internal position, indirect muscle pulling such as electric shock and epilepsy. It is clinically underdiagnosed in 95% of cases and should therefore be taken very seriously. Why is there a tendency to underdiagnosis? After a traumatic injury to the shoulder joint itself, the shoulder joint movement is limited and the shoulder joint appears painful with no specific symptoms. It is not easy to see the dislocation of the shoulder joint on orthogonal radiographs, and the shoulder joint is mainly dislocated in the anterior direction, so if we do not pay attention to it, posterior shoulder dislocation is very easy to be missed. What are the clinical manifestations of posterior shoulder dislocation? Posterior shoulder dislocation tends to appear as follows: limited external rotation of the shoulder joint; limited supination; anterior hollowing of the shoulder joint; a piece of bony prominence (rostral prominence) in front is more obvious; posterior fullness of the shoulder joint, etc. If, however, we value it and suspect its presence, a CT alone will tell us everything. See the picture. If we ignore it and miss the diagnosis, it will easily lead to a defect in the shoulder joint bone, which will make the treatment difficult and will have a great impact on the function of the patient’s shoulder joint, and in some cases, the artificial joint will even have to be replaced.