Inclusion Criteria:  Subject is scheduled to undergo total knee arthroplasty under a short general anesthesia of less than 2 hours Subject's American Society of Anesthesiologists physical status is I-II. The subject's parent/legally authorized guardian has given written informed consent to participate.  Exclusion Criteria:  Subject has a diagnosis of bronchial asthma, coronary heart disease, severe hypertension, renal failure or liver failure. Subject has a diagnosis of Insulin dependent diabetes. Subject is allergy and contraindication to esketamine or ketorolac. Subject has a history of chronic pain, a history of alcohol or opioid abuse, pre- existing therapy with opioids. Subject has any contraindication for the use of patient-controlled analgesia (PCA). Subject is pregnant or breast-feeding. Subject is obese (body mass index >30kg/m^2). Subject is incapacity to comprehend pain assessment and cognitive assessment.