The patella is located in front of the knee joint and is the largest seed bone in the human body. The presence of the patella has a protective effect on the knee joint on the one hand, and on the other hand, it is able to stabilize the structure of the knee joint area and enhance the strength of the quadriceps muscle. Especially in the knee flexion and extension activities can play a leverage role, and can also effectively avoid the quadriceps tendon tissue on the cartilage of the femoral condyle to produce friction effect. So the patella is located in the knee joint part of the role of the knee joint is relatively large, if there is a patella trajectory poor or obvious patellar trauma, on the one hand, will reduce the strength of the quadriceps muscle; on the other hand, is prone to patellofemoral joint part of the cartilage surface abnormal friction, which will cause patellofemoral osteoarthritis, resulting in knee flexion and extension activities have obvious pain.