The sternal angle, also known as the angle of Louis, is a crucial anatomical landmark located at the junction between the manubrium and the body of the sternum. This landmark has several important clinical implications, particularly in relation to the great vessels and rib counting:
1. Site of Sternal Angle:
- The sternal angle is located at the level of the intervertebral disc between the fourth and fifth thoracic vertebrae.
- It is palpable as a horizontal ridge on the anterior surface of the sternum, where the manubrium articulates with the body of the sternum.
2. Relation to Great Vessels:
- Tracheal Bifurcation:
- The sternal angle is approximately at the level of the tracheal bifurcation into the right and left main bronchi.
- This makes it a clinically relevant landmark for airway management and procedures involving the trachea and main bronchi.
- Aortic Arch:
- The arch of the aorta is located behind the sternal angle at the level of the second intercostal space.
- Clinically, this is important for understanding the anatomical relationship between the aorta and the sternum.
- Superior Vena Cava (SVC):
- The sternal angle corresponds to the level where the superior vena cava pierces the pericardium to enter the right atrium of the heart.
- This anatomical relationship is significant in the context of central venous catheter placement.
- Innominate (Brachiocephalic) Artery:
- The innominate artery, a branch of the aortic arch, bifurcates into the right common carotid artery and right subclavian artery behind the right sternoclavicular joint, close to the sternal angle.
- This is relevant in the context of vascular surgeries and interventions.
3. Importance in Rib Counting:
- The second rib articulates with the sternum at the sternal angle.
- The sternal angle is used as a consistent reference point for counting ribs and intercostal spaces.
- Clinicians often begin counting ribs at the sternal angle, making it a standard starting point for rib numbering.
4. Cardiac Examination:
- The sternal angle provides an approximate reference for the level of the heart and great vessels.
- During cardiac examinations, clinicians may use the sternal angle as a guide for locating important anatomical structures.
5. Radiological Reference:
- In radiological studies, the sternal angle is used as a marker for identifying the level of the thoracic vertebrae and associated structures.
Understanding the significance of the sternal angle is crucial for healthcare professionals, particularly in fields such as surgery, cardiology, radiology, and emergency medicine. It serves as a reliable landmark for anatomical reference and plays a role in various clinical assessments and procedures.