PainAnalgesics, OpioidReceptors, Opioid, muReceptors, OpioidPain MeasurementReceptors, Opioid, deltaReceptors, Opioid, kappaPain ManagementPain, PostoperativeChronic PainOpioid PeptidesPain, IntractableAnalgesicsMorphineBack PainPain ThresholdOpioid-Related DisordersFacial PainNarcotic AntagonistsAnalgesiaBrachial Plexus NeuritisTramadolLow Back PainOxycodoneNaloxoneNeuralgiaAbdominal PainNeck PainFentanylNaltrexoneDrug TolerancePain PerceptionChronic DiseasePelvic PainAcute PainAnesthetics, LocalEnkephalinsTreatment OutcomeEnkephalin, Ala(2)-MePhe(4)-Gly(5)-NarcoticsHyperalgesiaAnalgesics, Non-NarcoticPain, ReferredLidocaineSeverity of Illness IndexHemorrhoidsEnkephalin, D-Penicillamine (2,5)-EndorphinsReflex Sympathetic DystrophyBuprenorphineDynorphinsProspective StudiesDouble-Blind MethodShoulder PainAnalgesia, Patient-ControlledEnkephalin, LeucinePalliative CareAnesthesia, LocalMusculoskeletal PainNerve BlockFollow-Up StudiesVertebroplastyEnkephalin, Leucine-2-AlanineTime FactorsMiddle EastQuestionnairesFractures, Compressionbeta-EndorphinDiprenorphineNociceptive PainSacrumDisability EvaluationDose-Response Relationship, DrugBenzeneacetamidesRetrospective StudiesHerpes ZosterHydromorphoneMethadoneOsteoarthritis, KneeMorphinansRange of Motion, ArticularCross-Sectional StudiesNeoplasmsSpinal FracturesSpinal NeoplasmsArthroplasty, Replacement, KneeBone NeoplasmsAnemia, Sickle CellOsteoarthritisKnee JointPrevalenceInjections, IntravenousAnti-Inflammatory Agents, Non-SteroidalNociceptorsInjections, SpinalBenzomorphansQuality of LifePyrrolidinesAcute DiseaseSubstance Withdrawal Syndrome