There are protruding bones of the tailbone, physiologic factors, and pathologic factors, such as developmental malformations, fractures, and localized masses. 1. Physiological factors: most of them are seen in people with thin body type, because of their thin body type, the tailbone lacks muscle coverage, and often the tailbone is more prominent in this position. 2. Pathologic factors (1) Congenital caudal developmental deformity: there is no obvious discomfort in this case, and generally do not need special treatment, mainly to avoid local compression, so as not to cause tail pain and other symptoms. (2) Fracture: if recently suffered trauma, it may cause fracture or misalignment, resulting in protrusion, usually accompanied by swelling and pain, and can be clarified by radiography and other examinations. (3) Localized swelling: for example, fibroma, lipoma, etc., which are generally benign lesions and do not cause pain and other uncomfortable symptoms, small swellings generally do not need to be dealt with, while large swellings can be surgically removed. There are many possible reasons for the protruding bone in the tailbone, it is recommended to consult a doctor for examination and treatment under the doctor’s guidance.