Corpus: Sternum

The sternum is a flat bone that forms the front border of the thorax. The ribs are attached to it directly or via cartilaginous connections.

2.1. Overview

The sternum can be divided into three sections:

• Manubrium of sternum: The "handle" of the sternum.
• Body of sternum
• Xiphoid process of sternum

These three sections are connected to each other via cartilage bridges known as:

• Manubriosternal symphysis and
• Xiphisternal symphysis.

The obtuse and easily palpable angle between the manubrium and body in the sagittal plane is called the sternal angle. The second rib attaches at this point.

2.2. Manubrium of sternum

The manubrium of the sternum is the widest and most cranial part of the sternum. It forms joints with the two clavicles at the sternoclavicular joints. At its cranial end, there is a trough-shaped depression called the jugular notch, which can be felt through the skin between the medial ends of the clavicles. The manubrium articulates with the first rib and the upper part of the second rib laterally. Between the cartilaginous depressions for these ribs, the lateral sides of the manubrium taper medially towards the body of the sternum. The superior sternopericardial ligament attaches to the posterior surface of the manubrium.

2.3. Body of sternum

The body of the sternum is the longest section, consisting of a flat bone that is marked by three transverse ridges at the levels of the third, fourth, and fifth ribs. These ridges serve as part of the origin for the pectoralis major muscle. On both sides of the body, there are depressions known as costal notches, which, together with the cartilages of the ribs (3rd to 6th), form the sternocostal joints. The second and seventh ribs each partially articulate with the body of the sternum. The bone between these hollows bulges outward. The cranial end of the body articulates with the manubrium, while the caudal end connects to the xiphoid process.

2.4. Xiphoid process

The xiphoid process is a sword-shaped cartilaginous process of the sternum, which is usually ossified in adults (> 40 years). It serves as the origin of the diaphragm and the rectus abdominis muscle. As a variant, the process can be split into two parts.

As the xiphoid process can easily break off and then be dislocated, during cardiopulmonary resuscitation the force of the cardiac massage should be applied above the xiphoid process in the caudal section of the body of sternum.

2.5. Positional designations

Positional terms related to the sternum include:

• Parasternal
• Suprasternal
• Infrasternal
• Substernal

Norm variants of the sternum include conditions such as hole sternum and cleft sternum.

Deformities include funnel chest (pectus excavatum), keel chest (pectus carinatum), and Harrenstein's deformity.

In adults, the sternum usually still contains red (hematopoietic) bone marrow, making it a site for bone marrow puncture. However, sternal punctures are now rarely performed due to the risk of puncturing the pericardium or ventricles. This procedure has largely been replaced by iliac crest puncture, which is less painful and carries fewer risks.

Thoracic trauma can result in a sternal fracture. Surgical transection of the sternum to access the chest cavity is referred to as a sternotomy. Pain in the sternum is often called chest pain or more specifically sternalgia.

In X-ray imaging, the space behind the sternum seen on a lateral X-ray of the thorax is referred to as the retrosternal space.