The best time to put a cast on a fracture is within a few hours to 3-4 days after the injury, because the soft tissues are not completely swollen within a few hours after the injury, and the cast is a protection for the fracture end at this time, in addition, about 3-4 days later is the peak of edema, the soft tissues are gradually swollen, so it should be regularly observed to see if the cast is too tight. 3-4 days later, the swelling begins to gradually reduce, and by about a week, the swelling begins to gradually subside. After 3-4 days, the swelling starts to decrease gradually, and the swelling starts to subside gradually in a week or so, and during this period, it is necessary to observe whether the cast is loose, and if it is loose, it needs to be replaced or adjusted in time. In addition, during this period of time, the soft tissue swelling may cause displacement of the fracture. Generally, it is necessary to review the X-ray film in about 7 days after the external fixation of the fracture cast to prevent the displacement of the fracture and the deformed healing.