Sternum

Anatomical point

• The anterior surface of the manubrium sterni is convex from side to side and concave from above & down.
• The superior border of the manubrium sterni is thick.
• Juglar notch lies centrally.
• Three ill-defined transverse ridge lies anteriorly.

Parts of sternum

1. Upperpart is manubrium sterni
2. The middle part is the body
3. The lower part is the xiphoid process

Manubrium sterni

• It is roughly quadrilateral in shape.
• It lies opposite to 3^rd and 4^th thoracic vertebrae.
• It is the thickest and strongest part of the sternum.

Features

1. Two surfaces - Anterior surface and Posterior surface
2. Four borders- superior, inferior, and two lateral borders

Anterior surface

Attachment

1. Sternal head of the sternocleidomastoid and pectoralis major muscles are attached on each side.

Posterior surface

Attachment

1. Two muscles are attached on each side

• Sternohyoid at the level of the clavicular notch
• Sternothyroid at the level of the facet for the first costal cartilage

2. The lower half is related to the arch of aorta

• The upper half is related to three branches of the aorta

         i.e brachiocephalic artery left common carotid artery, left subclavian artery, and left brachiocephalic vein.

Upper border

• It represents a notch called suprasternal notch or jugular notch
• It provides attachment to the interclavicular ligament.
• Either side of the clavicular notch there is a suprasternal notch that articulates with the clavicle to form the sternoclavicular joint

Lateral border

• Upper facet articulates with the first costal cartilage to form the primary cartilaginous joint.
• Lower demi facet along with other demi facets in the body of the sternum articulates with the second costal cartilage to form secondary cartilaginous joints.

Lower border

• It articulates with the upper end of the sternum and forms manubriosternal joint which is a secondary cartilaginous joint.
• The manubrium makes a slight angle with the body at a junction called the sternal angle or angle of Louis.

Body                     

• The upper end forms the manubriosternal joint.
• Lower end articulates with the xiphoid process to form a secondary cartilaginous joint called the xiphisternal joint.
• On the anterior surface three faint transverse ridges present called sternebrae.
• Lower parts of its posterior surface give origin to the sternocostalis muscle.
• Its lateral border articulates with the 2^nd -7^th costal cartilage to form a plane type of synovial joint i.e. is chondrosternal joint.

Xiphoid process

• Its anterior surface provides insertion to the medial fibers of the rectus abdominis.
• Its posterior surface gives origin to the sternal fiber of the diaphragm.
• Its tip provides attachment to the upper end of the linea alba.

Importance of sternal angle

• It's an important surface bony landmark.
• Corresponding to this angle second costal cartilage articulate which helps in counting the ribs.
• It lies at the level of the intervertebral disc between the T4 and T5 vertebrae.
• Ascending aorta ends at this level
• Arch of aorta begins and ends at this level.
• Descending aorta begins at this level.
• The trachea bifurcates into the right and left principal bronchi at this level.
• Pulmonary trunk divides into the right and left pulmonary arteries at this level.