The formation of ossifying myositis generally requires the following 4 factors: 1) trauma from external sources: about 70% of cases have a history of trauma, which can result in local hematomas, with only a collagen fiber layer and a small amount of skeletal muscle tears in mild cases, or severe muscle damage and extensive fractures in severe cases. 2) injury signal: this signal is likely to be secreted by the injured cells or by reactive inflammatory cells that reach around the injured tissue. 3) To have mesenchymal cells with defective or undefined gene expression. These cells can induce chondrogenesis or osteogenesis and differentiate into chondrocytes or osteoblasts after receiving appropriate signals.4) The presence of an environment in which continuous ossification of tissue occurs, of which signaling genes are the most critical. It is well documented that the signaling genes are the most critical, and Urist named them bone morpho genetic protein (BMP). The important ones include BMP type 1-12 and growth differentiation factor (GDF) type 5-7. Zheng Yinhua, Department of Rehabilitation, First Hospital of Jilin University, has also reported the formation of heterotopic ossification by the following factors in addition to trauma.1) Genetic: It is summarized into two major syndromes: fibrodysplasiaossificans progressive (FOP) and progressive osseous myositis hetero-plasia , POH), characterized by the accumulation of ectopic bone in multiple joints, patients eventually become severely disabled or even die. 2) neurogenic: in the extremities and skeletal muscle fibrous tissue more often, patients often have spinal cord injury or cranial injury, also seen in long-term coma disease. 3) post-arthroplasty: occurs in the soft tissues of the extremities, ectopic ossification can occur in both hands and feet. Pathologically, it usually goes through 3 stages: 1) Trauma and inflammation: necrosis and bleeding of muscle tissue or inflammation, with corresponding swelling and hyperplasia of surrounding soft tissue, but calcification and ossification have not yet formed. 2) Granulation tissue: the edges of lesioned tissue appear as bands, dots, eggshells and lace-like gradations. Aggravated ossification and calcification (also called centrifugal calcification), the process of ossification and calcification develops from the periphery to the center of the lesion, for 3-4 weeks after the trauma. around 5-6 weeks, regular or irregular ring-shaped ossification can be formed around the lesion, the peripheral band is mature bone tissue, the middle band is bone-like tissue, and the central band is proliferating active fibroblast, the mass can have enlargement in this period, but the soft tissue swelling is reduced. In this period, it is difficult to differentiate from sarcoma if the pathological tissue is taken from the middle band or center of the lesion. 3) Ectopic ossification: The entire lesion tissue is ossified in the later stage, due to reduced soft tissue swelling and plasticity into a diamond or oval bone mass due to the internal stress of muscle tissue. The ossifying myositis matures with a typical three-layer structure of the mass. Under electron microscopy, the central layer is the hemorrhagic layer, visible as mesophagocytes, stromal cells and iron-containing heme; the middle layer is the atrophic muscle fiber layer, dominated by endothelial cells and fibroblasts; the outer layer is the ossification layer, visible as osteoclasts and bone cells. This article is authorized by Dr. Yinhua Zheng.