GROSS FEATURES OF STERNUM

Introduction

The sternum, also known as the breastbone, is a flat, elongated bone located in the center of the chest, connecting the ribs and forming the front part of the rib cage. It is a vital bone in the human body, providing attachment for muscles, cartilages, and ligaments that play crucial roles in breathing, movement, and stability of the thorax. In this answer, we will describe the location and shape of the sternum in detail.

A) Location of the Sternum:

The sternum is located in the center of the chest, between the two clavicles (collarbones) and the seven pairs of ribs. It extends from the base of the neck to the xiphoid process, a small bony projection at the lower end of the sternum that points towards the navel. The sternum is situated over the heart, lungs, and major blood vessels, protecting these vital organs and providing a bony framework for the attachment of muscles that move the arms and shoulder blades.

B) Shape of the Sternum:

The sternum is a flat, elongated bone with a curved shape, resembling a flat, horizontal rectangle with rounded ends.

 

Parts of the sternum

The sternum consists of three main parts: the manubrium, the body, and the xiphoid process.

1. Manubrium: The manubrium is the uppermost part of the sternum and is shaped like a trapezoid. It is wider at its superior end and narrows down towards its inferior end where it articulates with the body of the sternum. The superior surface of the manubrium contains a shallow concavity called the suprasternal notch or jugular notch, which can be easily felt at the base of the neck. This notch serves as an attachment site for various muscles and ligaments.

2. Body: The body of the sternum, also known as the gladiolus, is the largest and longest part. It is roughly rectangular in shape and extends inferiorly from the manubrium to the xiphoid process. The body consists of four segments called sternebrae, which are separated by transverse lines known as sternal angles or sternal notches. These notches mark the points of articulation with the costal cartilages of ribs 2 to 7.

3. Xiphoid Process: The xiphoid process is the smallest and most inferior part of the sternum. It is thin and elongated, resembling a sword or dagger in shape. The xiphoid process is made up of hyaline cartilage during childhood but gradually ossifies and becomes bony in adulthood. It serves as an attachment site for some abdominal muscles and acts as a landmark for various medical procedures such as CPR (cardiopulmonary resuscitation).

In addition to these three main parts, the sternum also has several important features and landmarks. These include the clavicular notches on the superior border of the manubrium, which articulate with the clavicles (collarbones), and the costal notches on the lateral sides of the body, which articulate with the costal cartilages of ribs 2 to 7.

The sternum is a vital bone that provides structural support to the chest and plays a crucial role in respiration by serving as an attachment site for various muscles involved in breathing. It also protects the underlying organs from external trauma.

 

Articulations and muscle attachments of the sternum

The sternum, also known as the breastbone, is a flat bone located in the center of the chest. It plays a crucial role in protecting the vital organs in the thoracic cavity, such as the heart and lungs. The sternum consists of three main parts: the manubrium, the body, and the xiphoid process. Each part has specific articulations and muscle attachments that contribute to its function and stability.

1. Manubrium:
The manubrium is the superior portion of the sternum and is shaped like a trapezoid. It articulates with two main structures: the clavicles (collarbones) and the first rib. The articulation with the clavicles forms the sternoclavicular joints, which are synovial joints that allow for movement of the upper limbs. The articulation with the first rib forms the sternocostal joint, which is a cartilaginous joint that provides stability to the rib cage.

Muscle attachments on the manubrium include:

• Sternocleidomastoid muscle: This muscle attaches to the superior surface of the manubrium and plays a role in flexing and rotating the head.
• Pectoralis major muscle: The clavicular head of this muscle originates from the anterior surface of the medial half of the clavicle and attaches to the lateral aspect of the manubrium. It contributes to movements of the shoulder joint.
• Subclavius muscle: This small muscle originates from the first rib and inserts onto the inferior surface of the clavicle near its junction with the manubrium. It helps stabilize and depresses the clavicle.

2. Body:
The body of the sternum is elongated and forms the largest portion of this bone. It consists of four segments called sternebrae, which are separated by transverse ridges. The body articulates with the second to seventh ribs through costal cartilages, forming the sternocostal joints. These joints are important for the flexibility and movement of the rib cage during respiration.

Muscle attachments on the body of the sternum include:

• Rectus abdominis muscle: This muscle attaches to the inferior surface of the body of the sternum and plays a role in flexing the trunk.
• Transversus thoracis muscle: This muscle originates from the posterior surface of the lower sternum and inserts onto the internal surface of costal cartilages 2-6. It helps depress the ribs during expiration.

3. Xiphoid process:
The xiphoid process is the smallest and most inferior part of the sternum. It is a thin, cartilaginous structure that ossifies with age. Although it does not have any articulations, it serves as an attachment site for several muscles and ligaments.

Muscle attachments on the xiphoid process include:

• Rectus abdominis muscle: The inferior fibers of this muscle attach to the superior surface of the xiphoid process.
• Diaphragm: The central tendon of the diaphragm attaches to the posterior surface of the xiphoid process. The diaphragm is a crucial muscle involved in respiration.

In summary, the sternum has various articulations and muscle attachments that contribute to its function and stability. The manubrium articulates with the clavicles and first rib, while the body articulates with the second to seventh ribs. The xiphoid process does not have any articulations but serves as an attachment site for muscles such as rectus abdominis and diaphragm.

 

The relations of the sternum

The relations of the sternum are important in various clinical contexts. Firstly, it serves as an attachment site for several muscles involved in respiration and movement of the upper limbs. The pectoralis major and pectoralis minor muscles attach to the sternum, providing stability and strength during activities such as lifting or pushing. Additionally, the sternocleidomastoid muscle attaches to the manubrium and clavicle, allowing for movements of the head and neck.

Furthermore, understanding the applied anatomy of the sternum is crucial in medical procedures such as cardiac surgeries and chest compressions during cardiopulmonary resuscitation (CPR). During open-heart surgeries, the sternum is often divided longitudinally (median sternotomy) to gain access to the heart. After surgery, wires or plates may be used to stabilize and close the sternum.

In CPR, chest compressions are performed on the sternum to manually circulate blood when a person’s heart has stopped beating effectively. Proper hand placement on the sternum is essential for effective compressions and to avoid injury to underlying structures.

The sternum also has clinical importance in the diagnosis and evaluation of certain medical conditions. For example, sternal tenderness or pain may be indicative of conditions such as costochondritis (inflammation of the cartilage connecting the ribs to the sternum), sternal fractures (often caused by trauma), or infections such as osteomyelitis.

In addition, abnormalities or variations in the shape or structure of the sternum can be associated with congenital conditions such as pectus excavatum (sunken chest) or pectus carinatum (protruding chest). These conditions may cause cosmetic concerns or, in severe cases, affect respiratory function.

Overall, understanding the relations and clinical importance of the sternum is crucial for healthcare professionals in various medical specialties. It aids in accurate diagnosis, surgical procedures, and proper management of conditions affecting this vital structure.