In clinical practice, if a patient is given a cast for fixation after a fracture occurs, most of them can be performed without removing the cast for X-ray, CT film, MRI film and other examinations when the patient is reviewed. However, if the external fixation cast is too loose or too tight, it needs to be replaced in time, because too tight external fixation cast will compress the local area and affect the local blood circulation, which will easily develop tension blisters, or there will be swelling and pain at the end, which will easily develop necrosis of the end limb. If the external fixation cast is too loose, it will not play the role of fixation and will easily cause the fracture to be misaligned twice.