In orthopedic outpatient clinics, patients often ask: Which is better, MR, CT or X-ray? Or, if MRI is better than X-ray, why do I have to do both? Isn’t this an obvious duplication of tests? There are also patients who, in order to save trouble, often ask for CT instead of ordinary X-ray examination or ask for magnetic resonance imaging (MRI) instead of CT examination, thinking that MRI is clearer than CT and CT is clearer than X-ray. To replace X-ray and CT with MRI results, only 1 examination is required. In fact, these views are incorrect, the three means of examination can not replace each other. 1, X-ray X-ray is the first choice for the initial screening of disease, X-ray examination is inexpensive, suitable for most patients routine examination. It has good diagnostic value for diseases such as fracture dislocation, impermeable foreign body retention, cardiopulmonary organic disease, and digestive system obstruction. In addition, X-rays can detect diseases in which patients feel discomfort only when they change their position. Especially the power position examination, in the country is still very few can replace the X-ray examination with magnetic resonance. 2.CT CT can show the vascular lesions, CT examination in the display of cross-section is obviously better than the X-ray film, especially for the high density of the tissue image is clear, for the measurement of the distance between the bony structure of the high accuracy. CT can clearly show the direction of the blood vessels and vascular lesions, the sensitivity of the examination of the tumor is obviously higher than the ordinary X-ray film. Moreover, multi-row spiral CT is capable of three-dimensional imaging, which helps to show tissue and organ lesions in three dimensions. However, CT scanning is limited to the technician’s different levels of specialization and scanning level interval limitations, and cannot read the information of the examination area as a whole, resulting in a certain rate of missed diagnosis. In addition, CT on soft tissue imaging clarity and resolution is not high. 3, MRI MRI check soft tissue effect is better, MRI and X-ray and CT inspection is the biggest difference is that the inspection process is no X-ray radiation, the body damage is very small. It is mainly used to find soft tissue diseases, and in orthopedics, it is mainly used to find intervertebral disc lesions, crural lesions, meniscus lesions, inflammatory lesions and hemorrhagic lesions. Through the impassable processing technology can be early detection of cancellous bone fracture, such as: vertebral fracture, pelvic fracture; early detection of inflammatory diseases, such as: aseptic necrosis of the femoral head, bone tuberculosis, bone tumors, etc. MRI for vascular diseases with high sensitivity. However, there are also shortcomings: first, the general MRI examination cost is relatively expensive; second, each part of the examination time is long; third, the imaging accuracy of some bone tissues is not as good as CT; and the cost of dynamic MRI is 10 times more than that of dynamic X-ray film. Therefore, in the diagnosis, X-ray examination is preferred for crural fracture, crural slippage, crural deformity, crural instability and other diseases; MRI examination can be used for determining whether it is a fresh fracture or not; MRI is preferred for diagnosing intervertebral disc pathology, especially cervical spondylosis; and MRI is preferred for examining crural morphology, crural deformity, crural tumor, and crural tuberculosis; MRI is preferred for diagnosis of crural fracture, vertebral canal pathology, and articular synovial joint pathology; and MRI is preferred for diagnosis of crural fracture, spinal canal pathology, and articular synovial joint pathology. CT has irreplaceable advantages in the diagnosis of vertebral column fracture, spinal canal lesion, and articular synovial joint lesion. In conclusion, the three examinations are not interchangeable, and the more expensive the examination, the better it can detect the problem.