Angle of Louis

Angle of Louis, also known as the sternal angle, angle of Ludovic, or manubriosternal junction, is a significant anatomical landmark located on the anterior aspect of the thorax. It is formed by the junction between the manubrium and the body of the sternum. This bony prominence serves as a crucial reference point in clinical and anatomical settings for the identification of various thoracic structures.

Anatomy

The angle of Louis is located at the level of the second rib's costal cartilage and corresponds to the T4-T5 vertebral level. It marks the site where the second ribs attach to the sternum, making it an essential landmark for rib identification. The angle typically projects at about 160 degrees and can be palpated easily on most individuals. It is more pronounced in men than in women.

Clinical Significance

The angle of Louis has several clinical implications. It serves as a reference point for:

• Locating the aortic arch, the bifurcation of the trachea into the right and left main bronchi, and the start of the ascending aorta and the end of the descending aorta.
• Identifying the site for central venous catheter insertion in the internal jugular vein or subclavian vein.
• Counting the ribs and intercostal spaces, which is crucial in procedures such as thoracentesis and in the assessment of chest injuries.
• Determining the level of the diaphragm during respiratory assessment.

Educational Importance

In medical education, the angle of Louis is emphasized as a landmark for students to learn thoracic anatomy and to practice physical examination skills. Its recognition is vital in the accurate assessment of the chest and in performing procedures that require anatomical precision.

Historical Aspect

The angle of Louis is named after Antoine Louis (1723–1792), a French surgeon and anatomist. The naming honors his contributions to the field of medicine and his role in the development of anatomical nomenclature.