Costochondritis is inflammation of the junctions where the upper ribs join the cartilage that holds them to the breastbone (sternum). Costochondritis causes localized chest wall pain and tenderness that can be reproduced by pushing on the involved cartilage in the front of the rib cage.Costochondritis is a relatively harmless musculoskeletal chest pain and usually resolves without treatment.ostochondritis causes localized chest wall pain and tenderness that can be reproduced by pushing on the involved cartilage in the front of the rib cage. Costochondritis is a relatively harmless musculoskeletal chest pain and usually resolves without treatment.