A periosteal reaction usually means that there is destruction or damage to the bone. Histologically, an increase in osteoblasts in the inner layer of the periosteum can be seen, resulting in the formation of new bone trabeculae. Periosteal new bone is produced by increased activity of osteoblasts in the inner layer of the periosteum in pathological conditions. Many diseases can have a periosteal reaction, such as acute septic osteomyelitis. Why does acute septic osteomyelitis cause a periosteal reaction? Etiology: Pathogenic bacterial infections (36%): Staphylococcus aureus haemolyticus is the most common causative agent, with Streptococcus b taking second place. Generally, the causative organism enters the blood circulation from the foci of infection located at the skin or mucous membranes when the primary foci are improperly treated or when the body’s resistance is reduced. And the bacterial tether is obstructed in the capillaries of the long bone epiphysis, where it is deposited and causes infection. Local trauma (25%): Local trauma may be the causative factor. It is a direct infection. Open fracture caused by firearm injury or other trauma, wound contamination, and infection without timely and thorough debridement is traumatic osteomyelitis. Inadequate aseptic operation during bone and joint hand master can also cause septic infection.