Sternal Angle Of Louis–
Surface landmark- It is felt 5 cm below the suprasternal notch as a tranverse prominence. It marks the joint between Manubrium and sternum- Manubriosternal joint. It lies at the level of 2nd costal cartilage anteriorly and between T4-5 vertebra posteriorly.
It is a significant landmarks as –
1. Ribs are counted from this level to downwards. 2nd rib lies at sterna angle.
2. It marks the plane of sepraration of superior and inferior mediastinum.
3. Ascending aorta ends, arch of aorta starts and ends and descending aorta begings at this level.
4. Trachea divides into 2 principle bronchi .
5. Azygous vein arches over the roof of the Rt. Lung and opens in SVC.
6. Pulmonary trunk divides into 2 pulmonary arteries below this level.
7. Thoracic duct crosses from right to left side and reaches left side at the level of sterna angle.
8. It marks the upper limit of the base of the heart.
9. Cardiac plexus are situated at the same level.
Source: BD Chaurasia Human Anatomy I