Q-angle abnormality is one of the clinical symptoms of patellar instability, which is a common cause of anterior knee pain, a common disorder of the patellofemoral joint, and an important cause of chondromalacia or osteoarthritis of the patellofemoral joint.Q-angle abnormality can be divided into laboratory tests and other ancillary tests, for which there are no relevant laboratory tests. Other ancillary tests are described below. Patellofemoral radiography is commonly used to diagnose patellofemoral instability and usually includes frontal, lateral and axial images of the patellofemoral joint. The latter is more relevant in the diagnosis of patellofemoral joint disease. The patient is placed in a supine position with the feet together and the toes up, so that the quadriceps are completely relaxed, and an anteroposterior view is taken to observe: patellar position, patellar height, patella and condyle shape. The lateral position can show signs of subchondral sclerosis and osteoarthrosis of the patella, and is often used to determine the presence or absence of a high patella. It has clinical significance in detecting whether there is an abnormal Q-angle. The measurement of patellar height varies from scholar to scholar. 3, axial position (patellofemoral joint cut) Axial X-ray examination of patellofemoral joint stability is more important in the diagnosis, not only can be used to understand whether the patellofemoral relationship is suitable, the presence of Q angle abnormalities can also be used to determine whether the direction of the lateral patellar trabeculae changes, and whether there is an excessive lateral-pressure syndrome (etc.). For joints with patellar instability, double imaging of the knee joint can not only observe changes in the patellar cartilage, but also compare the supporting ligaments on both sides of the patella and diagnose synovial crease syndrome and Q-angle abnormalities.