Direct impact to the bone frequently results in a sternum fracture, or break in the breastbone. The swelling of the joints caused by sternum fractures can also cause popping in this location. Using your hands to perform a push-up action can compress one of these bones, causing pain and injury. A blow to the chest that does not involve breaking the bone may result in pain at the site where the collarbone and rib cage join. The person might also feel pain in their shoulder or arm. Such injuries are usually treated by a doctor who will determine if surgery is needed to fix the broken bone or stitch up the wound. The sternum is the main support of the chest wall and acts as a protective barrier between the thoracic and abdominal cavities. It is made up of two parts: the manubrium (the upper part) and the xyphoid process (the lower part). The manubrium contains several large muscles that extend upward toward the neck; the xyphoid process has small irregular surfaces that help protect the spinal cord. The sternum and its associated tissues include many blood vessels, nerves, and lymph nodes. In general, the sternum is very resistant to trauma-related damage because it is made up of strong, thick plates of bone separated by tough ligaments.