Pectus excavatum is where excessively long ribs force the sternum deeper into the chest (nearer the spine) than is normal. This can cause the heart to be moved laterally within the thorax and thereby compromise surgical access to it.
It is caused by protein fibre deficiency which is a feature of many connective tissue disorders. It means bones are able to grow longer within the (weakened) soft tissue capsule, which limits their growth. In the case of the ribs, this can lead to excessive rib length which can cause pectus excavatum.
