Many outpatients after the occurrence of sports injuries, knee pain, instability, walking difficulties, joint swelling, the local hospital visit diagnosis of anterior cruciate ligament injury, synovitis, meniscus injury, etc., the result of the treatment is not ideal, the patient to participate in the work and sports, the reappearance of joint pain and instability, recommended by the local hospital doctor to me, I based on the injury at the time of the MRI, consider acute traumatic Patellar dislocation, which is a type of patellofemoral joint instability. Patellofemoral joint instability means that the patella is excessively displaced outward in extension and flexion activities, and patellar instability can be diagnosed by pushing the patella outward for more than 1cm when the knee is flexed at 30 degrees, or by a difference of 2mm in the patellofemoral gap on both sides on the axial radiograph. There are many reasons for patellofemoral joint instability, including anatomical variations, internal rotation of tibia, external rotation of femur, external rotation of knee, dysplasia of trolley, elevated patella, increased angle of patellar tilt, ligamentous laxity, abnormal position of obliquity head of medial femoral muscle, outward displacement of tibial tubercle, and tightness of lateral supportive band, etc., and it results in patellar dislocation or semi-dislocation to the outside of the knee when it starts flexion. Patellar dislocations not only cause soft tissue damage, but many also result in osteochondral defects due to the medial aspect of the patella impinging on the lateral aspect of the femoral condyle. Many patients are seen because of joint strangulation of the intra-articular free body, but by this time irreversible damage to the intra-articular cartilage and subchondral bone has already occurred. Patients with acute initial traumatic patellar dislocation can be treated conservatively, but developmental deformities of the joint should be excluded, as deformed joints are prone to re-dislocation, and the integrity of the medial patellofemoral ligament should be judged. For those patients with fixed patellar dislocation (patella can be in the dislocated position in any body position), it is difficult for us as experienced doctors to guarantee the postoperative results. In my case, many patients and their families have re-injured themselves because of the initial injury and simply did not discover the cause, just rested and then played sports, resulting in cartilage damage to the joint, which is very unfortunate!!!! What these patients need to be examined urgently is a CT of the knee or just an axial patella film, and once there is a patellar dislocation, an MRI of the knee should be added for the medial patellofemoral ligament. In such patients, if there is an indication for surgery, the medial patellofemoral ligament is usually reconstructed and the lateral supporting band is released, and if the deformity is severe, proximal and distal platysma surgeries may be added.