Periosteal reaction, also known as periosteal hyperplasia, is an increase in bone growth caused by stimulation of the periosteum and increased activity of osteoblasts in the inner layer of the periosteum, which usually indicates the presence of a lesion. Histologically, an increase in osteoblasts in the inner layer of the periosteum is seen, by new bone trabeculae. The periosteal reaction is not specific and is commonly seen in inflammation, tumors, trauma, and subperiosteal hemorrhage, as well as in normal growth and developmental stages. Differential diagnosis: diffuse periosteal thickening: pachydermoperiostosis is divided into two categories: primary and secondary. Primary is autosomal dominant. Secondary is often stimulated by liver, lung and gastrointestinal diseases or malignant tumors. The disease is more common in males. Proliferative periostitis: The periosteum is composed of dense connective tissue that covers the surface of the bone except for the articular surface and has many fibrous bundles that extend into the bone. In addition, tendons and ligaments attached to the bone are woven together with the periosteum at the site of attachment. As a result, the periosteum is very firmly bound to the bone. The periosteum is rich in blood vessels and nerves, which are distributed to the bone and marrow through the trophoblastic pores of the bone. The inner layer of the periosteum and the endosteum have the ability to differentiate osteoblasts and osteoclasts in order to form new bone and to destroy and transform the generated bone, so it is important for the occurrence, growth and repair of bone. During childhood, osteoblasts in the periosteum can continuously produce new bone tissue, thicken the surface of bone, and make bone grow thicker. Healing after fracture – bone regeneration – also relies on osteoblasts in the periosteum. If the periosteum is stripped too much during surgery, the nutrition and regeneration of bone will be impaired, affecting the healing of the fracture end and even causing bone necrosis. In the elderly, the periosteum becomes thinner and the differentiation of osteoblasts and osteoclasts is weakened, thus reducing the repair function of bone. Periostitis: Periostitis is a stressful periosteal injury or infectious periosteal injury caused by septic bacterial invasion due to periosteal and periosteal vasodilatation congestion edema or subperiosteal hemorrhage hematoma mechanized periosteal hyperplasia and inflammatory desperate changes. There is no specific clinical drug treatment, the key to care is to reduce activity, as much rest as possible, physical therapy with oral fenugreek type drugs can be relatively fast treatment.