Welcome to Just Answer and thanks for your question. That's a mouthful, isn't it? A "corticated ossific density" is a bone formation with an outer covering. The dorsal aspect is the back. The talonavicular joint is a little more complicated. The back side of the transverse tarsal joint of the ankle is composed of the talus and calcaneus bones, and the front side of the joint is composed of the navicular and cuboid bones. The area where the surfaces of the talus and navicular bones areopposed to one another is the talonavicular joint. See Fig. 14 in this link htttp://www.chionline.com/anatomy/anat3.html
This isn't a diagnosis, just a description of what was seen on the xray.
It doesn't address the issue of a case at all. The actual clinical examination and history will address whether a cast is needed or just immobilization for a time.