The sudden weakness of the patient’s right leg is commonly caused by osteoarthritis of the right knee joint, trauma to the right knee joint, etc., as follows: First, osteoarthritis of the right knee joint: there will be significant wear and tear of the articular cartilage, and the joint surface is not flat, and when walking or when the knee joint is weighted, there can be sudden symptoms of aliquot, resulting in sudden weakness of the right leg, and even easy to kneel down, taking MRI can find obvious damage to the patellofemoral articular cartilage MRI can reveal obvious damage to the patellofemoral cartilage. Second, trauma to the right knee joint: trauma to the right leg can occur during exercise, resulting in severe edema of the leg muscles, and the patient can experience sudden weakness of the right leg, as well as easy falls and limited movement, with very obvious local swelling, as well as painful local pressure and subcutaneous bruising, and sometimes even fractures can be detected by taking an X-ray. Therefore, patients with sudden weakness of the right leg should be diagnosed and treated early.