Today my son, age 14, was sitting in the car and suddenly cried out in pain. He grabbed his chest and then lifted his shirt to reveal a lump right about where the bottom rib attaches to the sternum. The best way I can describe it is that the lump looked like a knuckle when bent. We quickly pulled over and he said he needed to stand up. He stood up and stretched a bit, then sat back down and said it felt all better. The knot/lump disappeared. He went on the rest of the day with no complaints of pain, but I am still concerned.
Cramps in the rib cage would commonly present with such an experience, however a lump is not likely. Need to suspect rib trauma. I would suggest an X-ray of abdomen and ultrasonography can help us to rule out grave causes. Regards