Sternum Fracture * Damage to your sternum can cause swelling or popping around the bone. * Fractures may require surgical intervention. Muscle Strain * Injuring the muscles around the sternum or clavicle (collarbone) can cause sternum popping. * These muscles include pectoralis major, sternocleidomastoid, pectoralis minor. * Minor muscle injuries will heal themselves, but major injuries may require visiting a doctor. Costochondritis * Costochondritis is inflammation of the cartilage around your sternum. * Sometimes costochondritis has no obvious cause. However, minor injury, overuse of your arms, or respiratory infections are potential causes. Bone Dislocation * A dislocation at the sternoclavicular joint between your clavicle (collarbone) and sternum can cause a popping sound. * A common cause of dislocation at this joint is falling and catching yourself with your hands. No Apparent Cause * Sometimes there’s no obvious cause as to why your sternum is popping. It could be your muscles rubbing against your joint or gas being released from a joint capsule. * If it causes pain or discomfort, you should talk to your doctor.