Overview
The canine sternum is made of eight segments, the sternebrae (sternebrae), joined by intersternebral cartilages. The first is the manubrium (described on its own), followed by six cylindrical sternebrae and the xiphoid process. It forms the floor of the thorax, rises cranially towards the thoracic inlet and gives origin to the pectoral muscles.
Key features
- Sternebrae 2–7: short, cylindrical bones of similar size, slightly compressed laterally.
- Intersternebral cartilages: join consecutive sternebrae; they ossify in old dogs.
- Costal notches (incisurae costales): articular surfaces at the intersternebral junctions. The first costal cartilage articulates with the manubrium, the following ones at the junctions between sternebrae, and the eighth and ninth together at the last junction.
- Xiphoid process (processus xiphoideus): the last sternebra, flattened dorsoventrally, continued by the thin xiphoid cartilage (cartilago xiphoidea), to which the linea alba attaches.
Clinical relevance
- Pectus excavatum: dorsal deviation of the caudal sternum and costal cartilages that narrows the thorax; seen in puppies of brachycephalic breeds and may compromise breathing.
- Median sternotomy gives surgical access to the whole thorax.
- The sternebrae and their junctions should not be mistaken for lesions on lateral thoracic radiographs; calcified intersternebral cartilages are a normal finding in older dogs.
In this model sternebrae 2–7 and the xiphoid process are reconstructed by deforming the scanned manubrium, and the xiphoid cartilage is schematic.