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HeightenedFlexorWithdrawalResponseinIndividualsWithKneeOsteoarthritisIsModulatedbyJointCompressionandJointMobilizationCarolA.Courtney,PaulO.Witte,SamuelJ.Chmell,andT.GeorgeHornbyUniversityofIllinoisatChicago,Chicago,Illinois.Abstract:Patientswithchronicpainoftenpresentwithhyperalgesia,possiblyduetohyperexcit-abilityofnociceptivepathways.Theaimofthepresentstudywastoinvestigatealterationsinflexorwithdrawalreflex(FWR)excitabilityinindividualswithkneeosteoarthritis(OA)andthepotentialef-fectofspecificphysicalinputsortherapeuticinterventions(ie,jointcompressionandmobilization)onthesebehaviors.Tensubjectswithand10withoutkneeOA(age45–75)wererecruited.TheFWRwasexaminedutilizingsuprathreshold,noxiouselectrocutaneousstimuliappliedatthemedialfoot.Surfaceelectromyographic(EMG)wasrecordedfromthetibialisanterior(TA)andbicepsfemo-ris(BF),andpeakjointtorquesrecordedatthehip,knee,andankle.FWRthresholdwasascertainedandresponsesat2�thresholdrecordedafterthefollowingconditions:amaximal,volitional,joint-compressiontask,ashamhands-onintervention,andaGradeIIIoscillatoryjoint-mobilizationinter-vention.Adecreasedthreshold-to-flexorwithdrawalresponsewasfoundintheOAvscontrolgroup(P<.01).EMGandjoint-torqueFWRresponseswerefurtheraugmentedintheOAgroupfollowingthemaximaljoint-compressiontask(P<.05),yetremainedunchangedordiminishedincontrols.Jointmobilization,butnotshamintervention,reducedreflexresponsessignificantly,althoughprimarilybydecreasingBFactivityandkneetorques(P<.05).Perspective:ApplicationofspecificphysicalinputstoindividualswithkneeOAsimilartothoseencounteredduringactivityofdailylivingorduringtherapeuticinterventionsappeartomodulateinvoluntary,nociceptivereflexresponses.Routineweight-bearingactivitiessuchaswalkingmaypotentiallyenhanceheightenedFWRresponses,whilejointmobilization,acommonlyusedclinicalintervention,maydiminishreflexexcitability.ª2010bytheAmericanPainSocietyKeywords:Osteoarthritis,knee,jointmobilization,flexorwithdrawalreflex,pain,manipulation.Osteoarthritis(OA)affectsalmost40%ofthepop-ulationaged60andolder9andoftenleadstochronicpainanddisability.Withrecurrentarticu-lartissuedamage,stimulationofhigh-threshold(Ad,C)afferentstypicallyinitiatestheprocessesunderlyingchronic-painsymptoms.However,experimentaldatainchronic-painmodelssuggeststhatlow-threshold,typi-callyinnocuousinputsmayalsotriggerresponsesassoci-atedwithnoxiousstimulation.Specifically,peripheraland/orcentralsensitizationinchronic-painconditionsmayheightenpain-relatedresponsestononnoxious(Ab)inputs.18,20InpatientswithkneeOA5andotheror-thopedicrelateddisorders,2increasedexcitabilityofthenociceptivepathwayshasbeenobservedasadecreasedcurrentamplituderequiredtoelicitflexor-withdrawalreflexes(FWRs).Increasedexcitabilityofpain-relatedpathwaysmayexacerbateimpairmentsassociatedwiththeoriginalinsultandincreasedisability.Themechanismswhichallowmaintenanceorprogres-sionofheightenedFWRsinindividualswithOAareun-known,althoughcontinuedstimulationofAb(joint)receptorsincombinationwithAdandCinputsduringnormalweight-bearingactivitiesmayenhanceexcitabil-ityofnociceptivepathways.Severalstudieshavedemon-stratedincreasedhamstringactivationinpatientswithkneeOAduringwalkingandstairnegotiation,1,3,16whichwasthoughttoenhancejointstability.Analterna-tiveexplanation,however,isthatnoxiouskneeafferentstimulationduringjoint-compression-associated...