Inclusion Criteria:  Scheduled to undergo primary total knee arthroplasty in spinal anesthesia Able to perform a Timed Up and Go (TUG) test Age > 50 years old Ability to give their written informed consent to participating in the study after having fully understood the contents of the study American Society of Anesthesiologists (ASA) physical status 1, 2, or 3  Exclusion Criteria:  Patients who cannot cooperate Patients who cannot understand or speak Danish. Patients with allergy or intolerance to the medicines used in the study Patients with a daily intake of strong opioids (morphine, oxycodone, ketobemidone, methadone, fentanyl) Patients suffering from alcohol and/or drug abuse - based on the investigator's assessment BMI > 40 Diagnosed with chronic central or peripheral neurodegenerative disorders