Straight Leg Raising Test (SLRT) – Pathophysiology · Passive dorsiflexion of the foot (Braggard's test) · Applying firm pressure to lateral popliteal ...Epineuriumofsciaticnerve(likeallothernerves)iscontinuouswiththeduramaterwithingthespinalcanalwhichisfirmlyattachedtotheforamenmagnumaboveandthefilumterminalebelow.Intheelasticneuromeningealpathway,tensionappliedatonepointwillspreadthroughoutthelengthofspineuntilitisconstantallover.Flexionofthetrunkwouldlengthenthespinalcanalstretchingtheduraandextensionwouldshortenthesameresultinginrelaxation.First30degreesofSLRservestotakeuptheslackorcrimpinthesciaticnerveanditscontinuations.Between30and70degrees,thespinalnerves,theirduralsleevesandrootsoftheL4,L5,S1,andS2segments(S3rootdoesn’treachthelowerlimb)arestretchedwithanexcursionof2-6mm.Tensionandmovementfirstdevelopatthesciaticnotch,thenoverthealaofsacrum,thenasthenervecrossesoverthepedicle,andfinallyatintervertebralforamen.Thenerverootsalsomovelaterallytowardtheboneandthereforemoveintoaposterolateralherniationandpotentiallyawayfromacentralherniation.Thereforeamidlineherniationmaynotcausesciaticaduringstraightlegraisingandthetestwillbenegative.Movementofthenervepastneighouringstructresstopaltogetherasthelegisraisedpast70degrees.After70degrees,althoughthesestructuresundergofurthertension,otherstructuresalsobecomeinvolved.Inshort,followingeventsoccurinsciativenerveduringSLRtest:0-30degrees–Tonetheslack30-70degrees–Slidingandstretching70-90degrees–OnlystretchingA(normal)andB(discprotrusion)duringtensioningC(discprotrusion)andD(normal)duringrelaxationHere,itisimperativetomentionBreig’stissueborrowingphenomenon.Thetensionproducedinalumbosacralnerverootresultsindisplacementoftheneighboringdura,nerveroots,andlumbosacralplexustowardthesiteoftension.Ineffect,aborrowingoftherestingslackinneighboringmeningealtissuesoccursasneuralstructuresarepulledtowardthesiteofincreasedtension.Thisstretchinganddisplacementofthenerverootsplexireducestheavailableslackandpotentialmobilityoftheperiphe