Costochondritis Overview. Costochondritis is an inflammation of the junctions where the upper ribs join with the cartilage that holds them to the breastbone, or sternum. The condition causes localized chest pain that you can reproduce by pushing on the cartilage in the front of your ribcage.Costochondritis is a relatively harmless condition and usually goes away without treatment.The cause is usually unknown, but may happen from increased activity involving the arms. . Costochondritis (with unknown cause) is a common cause of chest pain in children and adolescents. 2  It accounts for 10% to 30% of all chest pain in children. 3  Annually, doctors evaluate about 650,000 cases of chest pain in young people ages 10 to 21. 4  The peak age for the condition is ages 12-14.