The manubriosternal joint (manubriosternal angle or angle of Louis) is a secondary cartilaginous joint (symphysis) between two parts of the sternum; the manubrium and the body of sternum. It is formed by the two irregular articular facets located on the inferior margin of the manubrium and the superior surface of the sternal body respectively. Between these two articular surfaces, there is a fibrocartilage disc that ossifies with age.
This joint allows a small amount of angulation between the longitudinal axes of the two sternal parts. This movement increases slightly the anteroposterior diameter of the thoracic cage facilitating the act of inspiration.
This article will discuss the anatomy and function of the manubriosternal joint
|Type||Secondary cartilaginous joint (symphysis)|
|Articular surfaces||Inferior margin of the manubrium of sternum, articular disc, superior margin of sternal body|
|Movements||Angulation, anteroposterior displacement|
The superior articular surface is located on the inferior border of the manubrium. The oval inferior margin is roughened for the attachment of the articular disc.
The inferior articular surface is located on the superior border of the body of sternum. Both articular surfaces are irregularly shaped and covered by hyaline cartilage.
Between these two facets, there is an articular disc composed of fibrocartilage. In most cases, it ossifies with age.
This joint is also known as the manubriosternal angle (angle of Louis) that serves as an important anatomical landmark. It is located approximately 7 cm below the upper margin of the manubrium. Being the location of the medial end of the second costal cartilage, this manubriosternal angle is a point at which clinicians can start palpating and counting ribs. For example, cardiologists use this anatomical landmark as the starting point for the physical exam since the angle of Louis is 5 cm above the right atrium. Also, the horizontal plane that passes through the joint and the articular disc between the fourth and fifth thoracic vertebrae divides the mediastinum into superior and inferior parts.
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The manubriosternal joint is enveloped in the fibrous membrane. On the anterior aspect of the joint, there is one sheet of fibrous tissue that supports the joint, referred to as manubriosternal ligament.
A small amount of movement is allowed in the manubriosternal joint. The total range of motion is approximately 7°. Most of this range of motion belongs to the angulation between the axes of manubrium and the body of sternum, followed by an additional superior displacement of the body of the sternum. This movement slightly increases the anteroposterior diameter of the thoracic cage facilitating the act of inspiration.
Learn more about the general features of the sternum by exploring articles, diagrams, videos and quizzes.