Posterior sternoclavicular dislocations are very rare and pose immediate threat to mediastinal structures should a patient sustain this type of injury. This case report discusses the presentation and diagnosis of a young male who presented with isolated right arm swelling after blunt trauma one day prior while participating in a bull riding rodeo event. He was diagnosed with posterior right sternoclavicular joint dislocation with compression of the left brachiocephalic vein that was seen on computed tomography (CT) angiogram study. Patient was transferred to a tertiary care center for a higher level of care and definitive reduction management. Any history of blunt shoulder trauma or direct sternoclavicular trauma with symptoms to suggest compression of mediastinal structures should make one suspicious for posterior sternoclavicular dislocation. Evaluation is best made by computed tomography (CT) scan. Reduction should be performed by an orthopedic surgeon in the operating room with cardiothoracic surgery available for any vascular compromise that may occur.TopicsSternoclavicular joint dislocations, trauma, orthopedics.