Breastbone

The sternum bone ([TA]: Sternum) or keel in some animals is a flat, odd, central thorax bone and symmetrical (usually), made up of several welded pieces (sternebrae). The sternum helps protect the heart and the anterior border of the lungs.

In humans

The sternum is made up of three parts, the handle or manubrium, the body and the xiphoid process or process i>, which has a highly variable shape. The manubrium and the body articulate in a symphysis forming the so-called sternal angle (Louis angle), which can ossify. The xiphoid appendix (or process) has an indefinite size (it can vary depending on the person, age...) and undergoes ossification from the age of 40, forming a symphysis where there was previously a sternoxyphoid synchondrosis. It has two faces, the front and back; two lateral edges; and two extremes, the upper or base and the lower or vertex.

The sternum is located in the middle and anterior part of the thorax, it articulates in its upper part with the clavicles and on its lateral edges the true ribs articulate through the sternocostoclavicular cartilage on the one hand while the false ones articulate on the other. by a single cartilage, which is attached to the 7th, 8th, 9th and 10th rib.

The articulation of the handle with the body is of the symphysis type and forms a fairly pronounced angle (approximately 35°) called the Louis angle at the level of the second rib, the most important articulation that It performs is with the first rib and with the clavicle forming the type of joint called sternocostoclavicular that in adult bones can become ossified and the first rib and the sternum are totally united, therefore the handle has two articular surfaces for said bones.

At the top of the sternum (base) is the sternal notch (or jugular), which serves as a free edge. It is possible to touch this edge of the breastbone just below where the neck ends. On the sides are the clavicular notches where the clavicles articulate, one on each side.

On the body there are 3 striations called cristae that are a trace of the embryonic ossification period.

Regarding the differences in sex, the male is usually larger, elongated and narrow. The notches are the junctional sites between the costal cartilages and the sternum.

Joints

Parts of the stern: manubrio (green), body (blue) and appendix xifoids (morado).

The costal cartilages of the first seven ribs unite with the sternum to form the sternocostal joints. The costal cartilage of the second rib articulates with the sternum at the sternal angle, making it easy to locate. The right clavicle articulates with the right sternal notch and the left clavicle articulates with the left sternal notch, respectively.

Malformations

There are two types of malformations of the sternum: keeled thorax and funnel-shaped thorax.

Retro-sternal pain

Retro-sternal pain is a type of pain characteristic of heart involvement (cardiac ischemia), consisting of oppressive pain, frequently radiating to the shoulder, arm, neck or epigastrium.

In animals

The sternum, in vertebrate anatomy, is a flat bone found in the front medial part of the rib cage. It is of endochondral origin. It probably first developed early in tetrapods as an extension of the shoulder girdle; it is not found in fish. In amphibians and reptiles it is typically a shield-shaped structure, often made entirely of cartilage. It is absent in turtles and snakes. In birds it is a relatively large bone and is usually in the form of a huge protruding keel, to which the muscles used in flight are attached. Only in mammals does the sternum take an elongated shape, and is segmented as in humans.

In chelicerates

In arachnids, the sternum is the ventral (lower) portion of the cephalothorax. It consists of a sclerite, located between the coxa, in front of the carapace.