Twelfth Rib

Key Features & Anatomical Relations

The twelfth rib is one of the two floating ribs of the thoracic cage. It is shorter and less curved than the eleventh rib. It is considered an atypical rib because it has no neck or tubercle and has only one articular facet on its head.

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

- parts: head, body, and costal end;

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

- landmark: articular facet on head.

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

The twelfth rib is located:

- inferior to eleventh rib;

- lateral to the twelfth costal cartilage, twelfth thoracic vertebra, and first lumbar vertebra.

It articulates with the:

- twelfth costal cartilage at the twelfth costochondral joint;

- twelfth thoracic vertebra at the joint of head of twelfth rib.

Ossification

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

- body, which appears in utero during the second month;

- head, which appears during puberty.

The ossification center for the head fuses with the body of the twelfth rib within the fourteenth to twentieth years (Cunningham, Scheuer and Black, 2016).

Variations

In some individuals:

- the twelfth rib may be fused with adjacent ribs;

- the costal end of the twelfth rib may be bifid in appearance (Tubbs, Shoja and Loukas, 2016).

Surface Anatomy

The costal end of the twelfth rib is easily palpated and is located by palpating two ribs down from the tenth rib.

List of Clinical Correlates

- Fracture of twelfth rib

- Aplasia of twelfth rib

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.