Ali taheriniya - Assistant professor of emergency medicine,Alborz university of medical science
Nasim beiranvand - medical intern of Alborz university of medical science

Abstract: Against anterior dislocation of shoulder, posterior dislocation of shoulder is rare condition that often missed to diagnosis. In other hand posterior dislocation of shoulder due to falling upon two hands is rare too. We present case with posterior dislocation of shoulder after falling and initial missed diagnosis. Introduction: Epidemiologic studies suggested that posterior shoulder dislocation accounts for approximately 1%–4 of all shoulder dislocations (1). Although shoulder dislocations are relatively common but posterior shoulder dislocations is rare and diagnosis of this condition often missed up to 80 (2, 3). It seems that the cause of miss diagnosis of posterior shoulder dislocation because of difficulty to diagnose it on the standard anteroposterior X-ray views (4). Seizures, electrocution and trauma are the common causes of posterior shoulder dislocation (5). rare complication in the setting of posterior shoulder dislocation is glenohumeral interposition of torn rotator cuff tendonsis that may lead to shoulder dysfunction (6). Other complications after posterior shoulder dislocation are osteoarthritis and avascular necrosis of the humeral head which occur due to chronic dislocations (3). Case report: We present 45 years old male teacher with chief complaint of mild pain of right shoulder. The pain was started from weeks ago and it was exist in active and passive motions of right shoulder and there was history of falling down upon two hands weeks ago due to an accident that patient discharged with no medication therapy. Past medical history was clear and patient did not take any drug. In physical examination vital sign was stable and no ecchymosis or ulcer exist. There was no tenderness and only external rotation was limited. Right shoulder x-ray was done (Figure 1). There was posterior dislocation of glenohumeral in x-ray. For confirming the diagnosis right shoulder CT scan with 3D reconstruction was done (Figure and 3). The diagnosis was confirmed .So close reduction in ED with sedation was done and right shoulder fixed with velpeau. Discussion: As we know Posterior dislocations can easily be missed on the anteroposterior X-ray projection, although initial diagnosis can be obtained with lateral (axillary) view. In other hand CT scan confirms the clinical suspect of posterior dislocation (7). Shoulder dislocations caused by lifting weight have been reported in the literature but shoulder dislocation due to falling upon hands is very rare condition. Our case had posterior dislocation of right shoulder due to falling upon two hands weeks ago which diagnosis was missed in initial evaluation. Conclusion: In patient with falling upon two hands with normal shoulder anteroposterior x-ray the posterior dislocation of shoulder should be rule out with lateral (axial) x-ray or CT scan in addition of good history taking and examination because of high rate of missing this diagnosis and its important complications like osteoarthritis and avascular necrosis of the humeral head. Therefore physicians should be aware of this diagnosis.