A periosteal reaction is the formation of new bone in response to injury or other stimuli of the periosteum surrounding the bone.[1] It is most often identified on X-ray films of the bones.[citation needed]
The morphological appearance can be helpful in determining the cause of a periosteal reaction (for example, if other features of periostitis are present), but is usually not enough to be definitive. Diagnosis can be helped by establishing if bone formation is localized to a specific point or generalized to a broad area. The appearance of the adjacent bone will give clues as to which of these is the most likely cause.[citation needed]
Appearances include solid, laminated, spiculated, and the Codman triangle.[4]