QS Study

Sternal angle (Angle of Louis):

It is a transverse ridge about 5cm below the suprasternal notch, making the manubriostemal joint. It is this angle formed between the manubrium of the sternum and the body of the sternum. Surgically, anatomically and medically, it is a vital anatomical landmark.

Situation

It lies at the level of the second costal cartilage anteriorly and the disc between 4th & 5th thoracic vertebrae posteriorly. It’s important because we know that this level marks the level of the intervertebral discs which lies between thoracic vertebra T4 and T5. The 2nd rib combines with the sternum at the sternal angle and makes it an important site for determining rib number.

Importance – It’s an important structure because it marks the location of other structures in the body.

  • The ribs are counted from this level.
  • It marks the plane which separates the superior mediastinum from inferior mediastinum.
  • Situated at the line of junction between two discontinuous dermatomes, C4 segment above and T2 segment below.
  • Sternum moves forward and backward at the steno-manubrial joint during respiration.
  • The ascending aorta ends at this level & the arch of the aorta begins and also ends at this level.
  • The descending aorta begins at this level.
  • The trachea divides into two principal bronchi.
  • The pulmonary trunk divides into two pulmonary arteries just below this level.
  • It marks the upper limit of the base of the heart.
  • The cardiac plexuses are situated at the same level.
  • Superior vena cava pierces the fibrous pericardium, and arch of azygos vein terminates.
  • Anterior margins of both lungs and pleurae approximate at the sternal angle.
  • Thoracic duct deviates from right to left behind the oesophagus, close to this level.