Knee bending, there is no so-called best time, usually can be based on different causes of the patient, the time range is different. 1. Patients with knee joint injury: usually, patients with knee joint injury, such as meniscus injury, periosteal injury, need to pay attention to rest in the early stage, fixed braking, which is conducive to the recovery of the knee joint. Premature bending exercise will damage the knee joint and aggravate the condition. Functional exercise of knee bending in the later stage is usually within one and a half to three months. 2. Post-artificial knee replacement patients: under normal circumstances, the day after the operation, you can perform knee flexion and extension exercises. This is because the earlier the patient performs knee flexion exercises, the lower the likelihood of joint stiffness and the faster the joint function is restored. 3. Patients after cruciate ligament reconstruction: It usually takes about one month before knee flexion and extension exercises can be performed. If the patient exercises too early, the reconstructed ligament may be loosened.