In orthopedic clinics, some patients often ask for CT instead of plain X-ray or magnetic resonance imaging (MRI) instead of CT because of mobility problems or to save time, thinking that MRI imaging is clearer than CT and CT is clearer than X-ray. To replace X-rays and CT with MRI results, only 1 examination is required. This view is incorrect, and the three means of examination are not interchangeable substitutes. X-ray is the first choice for initial screening of diseases X-ray is inexpensive and suitable for routine examination of most patients, especially for initial screening of diseases. It has good diagnostic value for fracture displacement, bone disease with bone alteration, bony lesions in joint areas, opaque foreign body retention, organic heart and lung disease, and digestive system obstruction. In addition, radiographs can detect diseases in which the patient feels discomfort only when changing position. Especially power position film examination, there are still very few MRI can replace X-ray examination in China. CT can show vascular lesions CT examination is significantly better than X-ray in showing cross-section, especially for high-density tissues with clear image and high accuracy for measuring the distance between bony structures. CT can clearly show the direction of blood vessels and vascular lesions, and the sensitivity of examination of tumors is significantly higher than that of ordinary X-ray. Moreover, multi-row spiral CT can perform three-dimensional imaging, which helps to display tissue and organ lesions in three dimensions. However, CT scan is limited by the different professional level of technicians and the limitation of scanning level interval, which cannot read the information of the examination site as a whole, resulting in a certain rate of missed diagnosis. In addition, the clarity and resolution of CT imaging of soft tissues is not high. MRI has a better effect on soft tissues. The biggest difference between MRI and X-ray and CT examinations is that there is no X-ray radiation during the examination, and the damage to the body is minimal. It is mainly used to detect soft tissue diseases. In orthopedics, it is mainly used to detect disc lesions, spinal cord lesions, meniscal lesions, inflammatory lesions and hemorrhagic lesions. MRI has a high sensitivity for vascular diseases. However, MRI also has disadvantages: first, the cost of general MRI examination is relatively expensive; second, each part of the examination takes longer; third, the imaging accuracy of some bone tissues is not as accurate as CT; and the cost of dynamic MRI is several 10 times more than dynamic X-ray film. Therefore, in the diagnosis of spinal fracture, spinal slippage, spinal deformity, spinal instability and other diseases, radiography is preferred; in determining whether a fracture is fresh or not, skimmed-phase MRI can be used; in the diagnosis of intervertebral disc lesions, especially cervical spondylosis, MRI is preferred, and in the examination of spinal cord morphology, spinal cord deformity, spinal tumor, spinal tuberculosis and other diseases, MRI is also preferred. CT has an irreplaceable advantage in the diagnosis of spinal fractures, spinal canal lesions, and arthrogryposis. In conclusion, the three tests are not interchangeable, and the more expensive the test, the more problems can be detected.