Side impact syndrome of the shoulder is rare and usually associated with concomitant mid-shaft clavicle, rib and scapular fractures. Visceral complications involve pleural cavity and/or lung injuries. The authors report two rare instances of posterior sternoclavicular dislocations with this entity. This association is rare and diagnosis can be overlooked in multitrauma patients especially when blunt thoracic lesions can be life threatening. The absence of a fracture of the clavicle after a high-energy side impact to the shoulder should suggest this diagnosis, which can be facilitated by systematic total body CT scan with 3D reconstruction. Management is surgical.