How do ribs develop embryologically?

Ribs develop from costal processes of the thoracic vertebrae. These processes elongate to form cartilaginous arches, which later ossify into the bony ribs we see in adults.

What are accessory ribs and why are they clinically significant?

Accessory ribs are extra ribs that form from costal elements in non-thoracic regions. The most common is the accessory lumbar rib, which is usually asymptomatic. The accessory cervical rib can compress the brachial plexus or subclavian artery, potentially causing superior thoracic outlet syndrome.

How does the sternum form during development?

The sternum forms from two mesenchymal sternal bars on either side of the anterior body wall midline. These bars convert to cartilage and fuse craniocaudally to create the cartilaginous model, which later ossifies into the adult sternum.

When does ossification of the sternum occur?

Sternal ossification occurs in stages. The manubrium and body ossify from five double centers between the 5th and 9th months in utero, with complete fusion by age 25. The xiphoid process ossification center appears around age 3 and fuses with the sternum around age 40.

What are the main congenital anomalies of the sternum?

The main congenital sternal anomalies include sternal foramen/cleft (incomplete fusion of sternal bars), pectus excavatum (posterior sternal displacement compressing the heart), and pectus carinatum (anterior protrusion of the upper sternum).

What is the clinical significance of a cervical rib?

An accessory cervical rib can compress the lower trunk of the brachial plexus or the subclavian artery. This compression may lead to superior thoracic outlet syndrome, causing neurological or vascular symptoms in the upper limb.

Ribs & Sternum Development – Thoracic Cage