The knee is one of the important joint of the body, as it helps bear part of the body's weight and also allow for a person to sit, bend or engage in various physical activities. If your mom is old then you will need to consult a doctor as to what is causing the symptoms, as when a person is older , the relation between symptoms and other underlying disorders is , therefore the safest thing to do is find out what the exact problem is by seeking professional medical advice...