First Rib

Key Features & Anatomical Relations

The first rib is one of the seven true ribs of the thoracic cage. It is the shortest, broadest, and most tightly curved of all the ribs. The first rib is also considered an atypical rib because it only has one articular facet on its head. It also has extra bony features that other ribs don’t have (i.e., the scalene tubercle and grooves for subclavian artery and vein).

The first rib is classified as a flat bone and includes the following bony features:

- parts: head, neck, tubercle, body, and costal end;

- surfaces: superior and inferior surfaces, and internal and external borders;

- landmarks: scalene tubercle, grooves for subclavian artery and vein, and articular facets on the head and tubercle.

More information regarding these and other bony features can be found in the Parts, Surfaces, and Landmarks tabs for this bone.

The first rib is located:

- superior to the second rib;

- inferior to the clavicle;

- lateral to the first costal cartilage and first thoracic vertebra.

It articulates with the:

- first costal cartilage at the first costochondral joint;

- first thoracic vertebra at the first costovertebral joint.

Ossification

Ossification of the first rib occurs at ossification centers found in the:

- body, which appears in utero during the twelfth week;

- head, which appears during puberty;

- tubercle, which appears during puberty.

The ossification centers for the head and tubercle fuse with the body of the first rib within the fourteenth to twentieth years (Cunningham, Scheuer and Black, 2016).

Variations

In some individuals:

- the first rib may be absent unilaterally or bilaterally;

- the first rib may have two heads, known as a bicipital rib, due to its fusion with either a cervical rib or the second rib (Tubbs, Shoja and Loukas, 2016).

Surface Anatomy

The superior surface of the first rib can usually be palpated at a location that lies posterior to the clavicle, anterior to the descending part of trapezius muscle and lateral to the sternocleidomastoid muscle.

List of Clinical Correlates

- Fracture of first rib

- Aplasia of first rib

- Asphyxiating thoracic dysplasia/Jeune syndrome

References

Cunningham, C., Scheuer, L. and Black, S. (2016) Developmental Juvenile Osteology. Elsevier Science.

Tubbs, R. S., Shoja, M. M. and Loukas, M. (2016) Bergman's Comprehensive Encyclopedia of Human Anatomic Variation. Wiley.