Sternoclavicular Joint Separation

Sternoclavicular separation is an uncommon sprain of the ligaments of the sternoclavicular joint (the junction between the breastbone [sternum] and the collarbone [clavicle]). When a ligament is overstretched, it becomes taut and gives way at its weakest point, either where it attaches to the bone or within its midsubstance. The sprain may range from where the collarbone keeps its normal position with respect to the sternum (nondisplaced) to the collarbone losing contact with the sternum. The collarbone may move outward (anteriorly) to become more prominent, causing a bump on the chest, or backward, behind the sternum (posteriorly).