periosteal

This term is used exclusively within medical and anatomical registers, specifically in orthopedics, radiology, and pathology. It describes a precise anatomical relationship to the periosteum, the fibrous membrane covering the outer surface of bones. In clinical reports, it often appears in the context of "reaction," referring to the formation of new bone in response to injury, infection, or malignancy.

Because it is a technical adjective derived from a specific anatomical structure, it does not have a casual or metaphorical equivalent. It is strictly descriptive and neutral in tone, used to localize a condition or a physiological process to the outermost layer of the bone.