NORMAL RIB DEVELOPMENT

The ribs develop from the mesenchymal costal process of the thoracic vertebrae during embryogenesis.

Chondrification of the ribs begin at about 6.5 weeks menstrual age with dorsoventral flattening of the thoracic cage starting 1 week later.

At the end of the embryonic period a well-formed cartilagenous thoracic cage is present. The ribs assume a horizontal position rather than the sloping orientation seen in adult life.

Primary ossification - Near the angle of the rib.
Secondary ossification centers appear at puberty.

Ventral ends of the cartilagenous ribs remain as the costal cartilage. When development is complete:

• 12 thoracic vertebrae, 12 pairs of ribs and costal cartilages.
• Anteriorly the superior seven costal cartilages articulate with the sternum.
• 8th, 9th and 10th cartilages articulate with the next cartilage above.
• 11th and 12th ribs are floating with no anterior articulation.

REFERENCES

1. Abuhamad AZ, Sedule-Murphy SJ, Kolm P et.al. Prenatal ultrasonographic fetal rib length measurement: correlation with gestational age. Ultrasound Obstet Gynecol 1996; :193-196.