Sternum

From ArticleWorld

The sternum is the long flattened bone extending from the sternal notch at its uppermost end to the xiphoid process at its lowermost end. It is located in the upper anterior thorax and partially covers the heart.

Anatomy

The sternum is about 17 cm long and consists of three articulated segments. The upper segment is called the manubrium. This bone forms articulations with the clavicle, with the first set of ribs and with the body of the sternum at its lower surface. A notch at each side of the lower border forms part of the articulation with the second ribs.

The body of the sternum is its longest portion. It articulates with the manubrium at its most superior part and with the xiphoid process at its most inferior aspect. Along the lateral border of the body, articulations exist for the second rib cartilage at the notch on the top lateral aspect, articulations for the fourth through sixth ribs and a small notch which partially articulates with the seventh rib.

The xiphoid process is the smallest portion of the sternum. It resides at the level of the inferior border of the heart and the superior border of the liver, marking the general place where the thorax and abdomen meet. The xiphoid process forms part of the articulation of the seventh ribs. As ribs 8-10 converge into the cartilage of the seventh rib, all of these ribs have some cartilaginous connection to the xiphoid process.

Function

The sternum provides support for the ribcage and clavicle and partially protects the heart and its main vessels. The sternum also provides muscular attachments as well. The sternocostal head of the pectoralis major muscle connects along the length of the sternum. This allows for the forward rotation of the shoulder. Along the lower part of the body, the transversus thoracis muscle originates. Several small neck muscles are attached to the manubrium of the sternum.

Conditions

The sternum is a strong bone that is rarely fractured. Some steering wheel traumas, however, can cause the sternum to fracture. Some children can be born with or develop a condition known as pectus excavatum. This is when the sternum is deeply indented along its length. Besides being an embarrassing abnormality, an individual with this condition can develop difficulty with pressure on the heart or lungs that is severe enough to require surgical correction.