Sternum

The National Cancer Institute (NCI) dictionary describes the sternum as the long flat bone that forms the center front of the chest wall, attached to the collarbone and the first seven ribs. The Real Academia Española dictionary defines the Spanish word, esternón, in similar terms: a flat bone located in the front part of the chest, with which the true ribs articulate at the front.

Pectus excavatum is a medical term that describes an abnormal formation of the rib cage that gives the chest a caved-in or sunken appearance. MedlinePlus explains that it is due to too much growth of the connective tissue that joins the ribs to the breastbone (sternum), which causes the sternum to grow inward. In its article on costochondritis (costocondritis), MedlinePlus en español says that all of the ribs except the last two are connected to the esternón by cartilage, and that the provider checks the area where the ribs meet the esternón.

Esternón is the word used by MedlinePlus en español, the National Cancer Institute's Spanish dictionary and the Real Academia Española dictionary. The RAE dictionary marks it as a masculine noun, so it takes el: el esternón, al esternón. It carries a written accent on the last syllable. The NCI dictionary adds that the bone is also called hueso esternal. English has two words for it in these sources, sternum and breastbone, and the NCI English entry treats them as the same bone.

The NCI Spanish entry supplies the neighbouring vocabulary: pared torácica (chest wall), clavícula (collarbone) and costillas (ribs). The RAE definition adds pecho (chest) and costillas verdaderas (true ribs). MedlinePlus en español, describing costochondritis, writes cartílago (cartilage) for the tissue that connects the ribs to the esternón, and describes a symptom as tenderness when pressing the area where a rib joins the esternón: la zona en la que la costilla se une al esternón.