Osteomyositis is most common in children and adolescents, preferably in males, and 60-75% have a history of trauma. The main clinical manifestations are localized lumps, accompanied by redness, heat and pain, and limited movement of the affected joints. It can be divided into 4 stages. (1) Reaction period: this period is usually 15-60 days after the trauma, and the swelling of the mass in this period becomes bigger, calcified and disappears faster. The size of the mass can be 5-12cm.(2) Active stage: fever and localized elevated skin temperature can occur, with tenderness and hardness on touch. (3) Mature stage: Shell-like bony cartilage may appear in this stage, and joint movement may be limited if joints are involved. (4) Recovery stage: the mass stops growing in this stage, and the mass may become smaller or even disappear after 1 year. However, most of them cannot disappear on their own, and are usually treated with medication or surgery after developing into the mature stage.