Pain, PostoperativeAnalgesics, OpioidAnesthesia, RectalPirinitramideAnalgesia, Patient-ControlledInfusions, IntralesionalMorphinePain MeasurementHydromorphoneOxycodoneReceptors, Opioid, muFemoral NerveReceptors, OpioidNerve BlockPostoperative Nausea and VomitingAnesthetics, LocalCyclohexanecarboxylic AcidsPainReceptors, Opioid, deltaReceptors, Opioid, kappaOpioid PeptidesDouble-Blind MethodChronic PainOxygen ConsumptionPain ManagementPain ThresholdNarcotic AntagonistsBack PainLow Back PainPain, IntractableNaloxoneOpioid-Related DisordersNaltrexoneAbdominal PainNeck PainAlcohol DrinkingPain PerceptionAnalgesicsEnkephalinsPelvic PainAcute PainFacial PainEnkephalin, Ala(2)-MePhe(4)-Gly(5)-NarcoticsPain, Referred