Fibrous dysplasia, monostotic: Excessive growth in a single bone of hard-fibrous tissue that replaces the normal bone tissue. Symptoms of monostotic fibrous dysplasia may include pain and fracture of the bone. Most cases are diagnosed in adolescence or young adulthood and remain unchanged throughout life. The outlook is usually very good. Monostotic fibrous dysplasia appears to be a different disorder from polyostotic fibrous dysplasia.