[Posterior shoulder luxations (author's transl)]

In one out of two cases, posterior shoulder luxation is a diagnostic, clinical, and radiological "trap", which we feel has no true justification. In fact, contrary to what is generally admitted, a good analysis of the frontal image can easily suggest the diagnosis in most cases. All that is required is knowledge of the two principal indirect signs of posterior luxation. Increase in size of the glenohumeral interline is almost constantly present (12 out of 14 cases), and the "compression-fracture" of the anterior face of the head is often visible (9 out of 14 cases). Furthermore, if a strictly frontal film of the glenohumeral interline is requested in all cases of shoulder injury, the diagnosis of luxation is evident as the head is projected into the glenoid cavity. Profile films must also be taken. When the luxation is of recent origin, axillary profile films are usually impossible to take, and trans-thoracic profile films of the upper end of the humerus are taken, even though these do not show the glenohumeral interline. For this reason, it is essential to request an immediate Bloom and Obatas' profile. This incidence confirms the presence of posterior luxation and enables the anterior face of the head and the posterior glenoid rim to be studied. The diagnostic value of the two principal indirect signs of posterior luxation, as seen in frontal films and Bloom and Obatas' glenohumeral profile, is undeniable. The joint prognosis depends, in fact, on how early treatment is applied.