Exostosis

An exostosis (plural: exostoses) is the formation of new bone on the surface of a bone. Exostoses can cause chronic pain ranging from mild to debilitatingly severe, depending on the shape, size, and location of the lesion. It is most commonly found in places like the ribs, where small bone growths form, but sometimes larger growths can grow on places like the ankles, knees, shoulders, elbows and hips. Very rarely are they on the skull.

They normally form on the bones of joints, and can grow upwards. For example, if an extra bone formed on the ankle, it might grow up to the shin.

When used in the phrases "Cartilaginous exostosis" or "Osteocartilaginous exostosis", it is considered synonymous with Osteochondroma. Some sources consider the terms to mean the same thing even without qualifiers, but this interpretation is not universal.

Fossil record

Evidence for exostosis found in the fossil record is studied by paleopathologists, specialists in ancient disease and injury. Exostosis has been reported in dinosaur fossils from several species, including Acrocanthosaurus atokensis, Albertosaurus sarcophagus, Allosaurus fragilis, Gorgosaurus libratus, and Poekilopleuron bucklandii.