Costochondritis is an inflammation of the cartilage that connects the inner end of each rib with the breastbone (sternum). It can occur in any age group and is most common in young adults. Exactly how common it is in the UK is not known but in the US costochondritis has been shown to account for 10 per cent of chest pain episodes in the community and 30 per cent of people with chest pain presenting as an emergency to hospital.