Figure 6. (a) Solid periosteal reaction which has absorbed onto the underlying cortex of the mid-tibia due to stress response. No fracture line is seen in the tibia but localized periosteal reaction at the superior aspect of the fibula indicates a fatigue fracture (arrow). (b) Langerhans cell histiocytosis distal humerus. There is a periosteal reaction indicated by a single lamella of bone, with a moth-eaten pattern of bone destruction. (c) Proximal tibial osteosarcoma. There is a spiculated periosteal reaction with a "hair-on-end" appearance at the posterior aspect of the diaphysis proximally, and diffuse medullary sclerosis with permeative destructive pattern indicates the underlying aggressive tumour.