Knee injuries or surgeries that require a period of brace or cast immobilization are bound to cause knee adhesions, stiffness, and even knee ankylosis if not treated properly. Therefore knee flexion and extension exercises are very important. The following is an introduction to knee flexion exercises. First of all, we need to understand the knee flexion angle: under normal circumstances, the knee is straight and flat on the bed, the knee flexion angle is 0 °, generally can be hyperextended, knee hyperextension more than 10 °, may be a joint laxity, as follows the left picture of the knee hyperextension is about 20-30 °. Knee flexion, the heel of the knee flexion can reach the hip of a relatively thin person, which is about 140-150° of knee flexion. Calculation of the knee angle: the angle between the extension of the thigh and the calf. Perform one knee flexion exercise per day. The process of knee flexion is: remove the brace → flex the knee to the target angle → maintain for 10 minutes → wear the brace → ice for 20 minutes. To bend the knee: If the knee is flexed less than 90°, you can sit and hang your leg, that is, sit on the edge of the bed and let your lower leg drop. If the knee is flexed more than 90°, you can sit on top of the wall or hang your leg in supine position. If the knee is flexed more than 100°, you can hold your leg in a seated position or hang your leg on your back.