The sternum (aka breastbone) is a flat bone located at the anterior midline of the thorax.
It has a ‘T’ shape – almost like a sword! 🗡
Embryologically the sternum develops from a left and right cartilaginous plates that unite in the midline. It was named after the word ‘Sternon’ which means chest in 17th century Greek.
It articulates with the clavicle and the costal cartilages of the upper 7 ribs (true ribs), while the 8th, 9th and 10th ribs (false ribs) are indirectly attached with sternum via costal cartilage of the ribs above.
Parts of the Sternum
The manubrium is a large quadrangular shaped bone that lies superiorly to the body of the sternum.
The topmost part of the manubrium has a shallow, U-shaped border called the jugular or suprasternal notch. You can feel this at the anterior base of the neck, between the medial ends of the clavicles. Either side of the jugular notch, there is a large fossa – the clavicular notch that articulates with the medial ends of the clavicles, forming the sternoclavicular joints.
The costal cartilages of the first rib and part of the second rib also articulate with the manubrium, and they fit into facets on its lateral border.
The lower border of the manubrium articulates with the body of the sternum at the sternal angle. This is where the second pair of costal cartilage attaches to the sternum and at the level of the inferior border of T4.
Clinically this junction is known as the Angle of Louis.