The disappearance of knee-jerk reflex may be a normal phenomenon, or it may indicate abnormalities in the central nervous system or nerve root injury. 1. Normal phenomenon: knee-jerk reflex belongs to deep reflex, which is easily affected by mental and psychological factors, and also affected by the inspector’s technique, which may be manifested as the disappearance of knee-jerk reflex, and the more you want to knock out the knee-jerk reflex, the more the reflex doesn’t appear, and it is a normal phenomenon if there is no other symptom. 2. Abnormalities of the central nervous system: If the patient has abnormalities of the central nervous system, such as cerebral hemorrhage, cerebral infarction and other diseases, resulting in the central nervous system is unable to innervate the parts of the body normally, the knee reflex will disappear. 3. Nerve root damage: if the patient suffers from lumbar disc herniation, spinal stenosis, or nerve root inflammation, etc., it will lead to nerve root damage and disappearance of knee reflex, and need to go to the regular hospital for medical treatment. If the organism appears the symptoms of knee-jerk reflex disappearance, after ruling out the normal phenomenon, it is recommended to seek medical treatment in time.