Manubriosternal Joint Dislocation: An Unusual Risk of Trampolining

Background: Manubriosternal joint (MSJ) dislocation is a rare but potentially serious injury that can be associated with concurrent injuries to ribs, lungs, or myocardium. Two distinct types of MSJ dislocation have been described in the literature: type I, involving posterior dislocation of the sternum due solely to direct trauma; and type II, involving the sternum being pushed anteriorly as a result of indirect trauma. Until now, the relationship between the nature of the forces acting on the sternum and the type of MSJ dislocation that results has been absolute, whereby indirect forces never cause a type I dislocation, and direct forces never result in a type II dislocation. Objectives: To describe a case demonstrating that type I MSJ dislocation can occur without direct trauma. Case Report: A 14-year-old boy developed sternal pain accompanied by an audible crack while executing a maneuver on a trampoline that required hyperflexion of the thorax. A lateral chest radiograph demonstrated a type I manubriosternal dislocation normally associated with direct trauma, as opposed to the more typical type II dislocation pattern one would expect to find in a hyperflexion injury. Conclusion: MSJ dislocations are classified into two groups, depending on the position of the sternum in relation to the manubrium. Each type of dislocation has been ascribed to either direct forces (for type I dislocation) or indirect forces (for type II dislocation). This case highlights that it is possible to have a type I dislocation in the absence of any direct sternal trauma.