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THETHIGH
ObturatorNerve
Anatomy
Theobturatornerveoriginatesfromtheanteriordivisionofthelumbosacralplexusmedialto
thefemoralnerve.Itthenpassesalongthemedialsideofthepsoasmuscle,alongthelateral
pelvicwall,andenterstheobturatorforamen,whereitdividesintotwo.Theanteriordivision
emergesfromtheobturatorcanal,runsovertheobturatorexternus,deeptothepectineus,and
thenpasses betweentheadductorlongusand brevis, where itinnervatesthesemuscles. The
pectineusistypicallyinnervatedbythefemoralnerve,butsometimescanbeinnervatedbythe
obturatornerve.Theobturatornervealsoinnervatesthegracilismuscleandasmallcutaneous
area in the medial thigh. The posterior division of the obturator nerve passes through the
obturatorexternusandthenrunsbetweentheadductorbrevisandtheadductormagnus,where
itinnervatestheobturatorexternus, andtheadductorportionoftheadductormagnus.Italso
givesoffcutaneoussupplytotheinferomedialportionofthethigh,justabovetheknee.
ModesofInjury,Diagnosis,Treatment
Neuropathiesoftheobturatornerveareuncommon,butcanoccurfrompelvictrauma,surgery,
orcompressionfrompelvictumors,mostcommonlybladdercancer.Thereisnoevidencethat
entrapment in the obturator foramen occurs. The most common symptoms are pain, leg
adduction weakness, and sensory loss over a small area of the medial thigh. Diagnosis is
clinical,butcanbeconfirmedwithelectrodiagnostictesting.
SciaticNerve
Anatomy
Thesciaticnervearisesfromthelumbosacraltrunkandupperpartofthelumbosacralplexus
(L4–S3nerveroots).Itthentravelsdownthewallofthepelvisandentersthethighthroughthe
greatersciaticforameninthehip.Inthethigh,itpassesunderthepiriformismuscle,whereitis
pronetocompression,andbetweentheischialtuberosityandgreatertrochanterofthefemur,
whereitcanbepronetoinjuryfromtrauma.Itterminatesatthesuperiorborderofthepopliteal
fossa as the tibial nerve (medial) and common peroneal nerve (lateral). It innervates the
hamstringmuscles(longandshortheadofbicepsfemoris,semitendinosus,semimembranosus),
whichareallextensorsofthehipexceptthebicepsfemorislonghead,whichisaflexorofthe
knee(Fig.6-7A).Italsoinnervatestheadductormagnus,whichaidswithhipextension.Ithas
nodirectsensoryinnervationsinthethigh,butitsdistalbranches(tibialandcommonperoneal
nerves)providesensationtomostofthelimbbelowtheknee.
ModesofInjury,Diagnosis,Treatment
Theprimarycauseofsciaticneuropathycanoccuraftermechanicaltraumatothehip.Sciatic
nerveinjurymostoftenoccursintheglutealregionorareaofsciaticnotch,fromhiptrauma,
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fracture,dislocation,andoccasionallyafterhipreplacement.Otherless commonreasonsfor
sciaticnerveinjuryintheglutealregionincludeincorrectinjectionstothebuttock(lateralside
issafe,medialsideisunsafe,Fig.6-7B),compressionfromprolongedbedrest,andmassor
hematomainthepelvicarea.
Piriformissyndromecanalsoinjurethesciaticnerveintheregionofthesciaticnotch,asit
comes in contact with a hypertrophied piriformis muscle. Common causes of piriformis
syndrome are repetitive movements of the muscles in the gluteal region, which occur with
skating, cycling, or climbing. This diagnosis, however, is one of exclusion and often
controversial.58Cardiac surgeryandintra-aortic balloonpumps canalso beassociatedwith
sciaticnerveinjury.Morerarely,lesionsofthesciaticnervecanoccuratthemid-thighfroma
femurmassorfracture,ornerveinfarction.
Patientstypicallypresent with painshooting downthe posterior aspectofthelegto the
foot.Ifthelesionisintheglutealregion,weaknessoccursinthedistributionofthehamstrings
(knee flexion), inadditiontothemuscles belowthe knee.If thedamage isinthe mid-thigh,
kneeflexionisspared,andweaknessonlyoccursbelowtheknee.Nomatterwherethenerveis
injured,thereisalwayssparingofhipflexion,extension,abductionand adduction,andknee
extension. Interestingly, the peroneal distributionofthesciatic nerve is often more affected
thanthetibialdistribution,despitetheentirenervebeing affected.Sensorylossinvolvesthe
entireperoneal,tibial,andsuralterritories.Sensationissparedabovethekneeandbelowthe
kneeinthedistributionofthesaphenousnerve(themedialcalfandarchofthefoot).Theknee
reflexisspared,whereastheanklereflexisoftenmissing.
Sciatic neuropathy is mainly a clinical diagnosis, but if the damage is severe enough,
findingsmaybeseenonEMGandNCS.Sometypicalfindingsincludereducedperonealand
sural sensory responses, normal saphenous sensory response, reduced tibial and peroneal
motorresponseamplitudes,anddenervation/reinnervationmusclepatterns.
Prognosisinsciaticinjuryisfavorable,withonestudyreportinggoodrecoveryin75%of
patients over a 3-year period without treatment. Lack of plantarflexion and dorsiflexion
involvementatinitialevaluationisafavorableprognosticsign.
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FIGURE6-7.A:Nervesofthethighastheycourseposteriorly.B:Illustrationofthesafeareaforglutealinjections
(FromAgurAM,DalleyAF.Grant’sAtlasofAnatomy.13thed.Philadelphia,PA:WoltersKluwer;2012,with
permission).
FemoralNerve
Anatomy
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Thefemoralnerveisthelargestnervethatemergesfromthelumbarplexus(rootsL2,L3,and
L4). Itforms inthepsoas muscle, descends betweenthepsoasand iliacusmuscle,andthen
tucksbeneaththe inguinalligament,lateral tothefemoral arteryandvein,toenter thethigh.
Here it innervates several muscles, including the iliacus muscle (hip flexion and internal
rotation),andthequadriceps,whicharekneeextensors(rectusfemoris,vastuslateralis,vastus
intermedius,vastusmedialis). Italso innervates thesartoriusmuscle, whichflexes,abducts,
andexternallyrotatesthehip.Itprovidessensationtotheanteriormedialthighviatheanterior
cutaneousbranches.Itendsasthesaphenousnerve,whichprovidessensationfromthemedial
aspectoftheknee,tothemedialmalleolusandarchofthefoot.
ModesofInjury,Diagnosis,Treatment
Similartosciaticneuropathy,femoralneuropathycanoccurforavarietyofreasons.Because
thefemoralnerveisprotectedwithinthepelvis,directcompressionhereisuncommon,butcan
occurfromhiporpelvicfractures,pelvicmasses,oriliacushematoma.Damagecanalsooccur
after hip replacements, abdominal or pelvic surgeries, inguinal lymph node biopsy, or
childbirth, most likely from compression of the nerve along the inguinal ligament from
prolongedlithotomyposition.
59,60
Other mechanisms ofinjuryincludeischemia, toxic injury,
anddirecttransection.
On examination,patients haveweaknessofthe quadriceps musclegroupwithsparingof
adduction(obturatornerve). Ifinnervationtothe iliopsoasmuscle is lost,weaknessmaybe
presentinhipflexion.Sensorylossoccursalongtheanteriorthigh,medialthigh,andextends
downalongthemediallegtothearchofthefoot.Thekneejerk(L4)isgenerallydecreasedor
absent.
Femoral neuropathyis usually a clinical diagnosis. Nevertheless, needle EMG canhelp
confirmthediagnosis.Findingsincludeweaknessofmusclesinnervatedbythefemoralnerve,
absence of weakness in muscles innervated by the obturator nerve, and compromised
saphenoussensorynervefunction.
Prognosisforincompletefemoral neuropathyisgenerallygood,withabouttwo-thirdsof
patientsachievingsatisfactorytoexcellentrecoveries.Thesmallerthedegreeofaxonalloss
onEMG/NCS,thebettertheprognosis.Ingeneral,treatmentissupportive,includingphysical
therapy and appropriate analgesia. If the mechanism of injury is hematoma compression,
drainage may be indicated. If the nerve is damaged directly, as in transection or ligation,
surgicalexplorationandnerverepairorgraftingmaybeconsidered.
LateralFemoralCutaneousNerve
Anatomy
Thelateralfemoralcutaneousnervebranchesdirectlyoffthelumbosacralplexus(L2,L3).It
emergeslateraltothepsoasmuscle,crossestheiliacus,andthenpassesunderneaththelateral
part of the inguinal ligament to enter the thigh. It runs on top of the sartorius muscle and
terminates as cutaneous sensory branches that innervate the lateral thigh. It innervates no
muscles.
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ModesofInjury,Diagnosis,Treatment
Thisnerveismostcommonlyinjuredasitpassesbeneaththeinguinalligament,whereitcan
become compressed, causing a syndrome known as meralgia paresthetica. Common risk
factors include obesity, old age, diabetes, pregnancy, and tight-fitting clothing.61 Patients
generallycomplainofparesthesiasandpain,whichradiatedownthelateralthightowardthe
knee.Inseverecases,fixedsensorylossofthelateralthighcanoccur.
Diagnosis is mainly clinical, based on the unique location of paresthesias. Also, there
shouldnotbeweakness,andthereshouldbenosensorylossbelowtheknee.Electrodiagnostic
studies have a limited role, but may show reduced response amplitude ifdamageis severe
enoughtoproduceaxonalloss.62Electrodiagnosticstudiescanalsobeusefultohelpexclude
plexopathyorradiculopathy.
Meralgia paresthetica is usually self-limited. Most patients respond to conservative
measuressuchasavoidingtight-fittingclothingorweightloss.However,ifsymptomsrecur,or
arerefractory,medicationssuchasgabapentinorcarbamazepinemaybehelpfulforreducing
symptomsofneuropathicpain.Morerarely,alocalnerveblockorsurgicaldecompressioncan
beconsidered.
THELEG,ANKLE,ANDFOOT
NeuroanatomyoftheLegandFoot
CommonPeronealNerve
Thecommonperonealnerveexitsthepoplitealfossabetweenthebicepsfemoristendonand
thelateralheadofgastrocnemius,coursinganterolaterallyacrossthefibularneck.Itthengives
offcommunicatingbranchestothesuralnerveandthelateralcutaneousnerveofthecalf.The
nervethenpiercestheperoneuslongusmuscleanddividesintodeepandsuperficialbranches.
Thedeepperonealnerverunsbetweentheextensordigitorumlongusandtheextensorhallucis
longus5cmabovetheanklemortise.Atapproximately1cmabovetheanklejoint,beneaththe
extensor retinaculum,the nervedividesintomedialandlateralbranches.The medialbranch
travelsparalleltothedorsalispedisartery.Thelateralbranchsuppliesproprioceptivefibers
totheanklejointandsensoryfiberstotheroofofthesinustarsi,travelinginafibroustunnel
beneaththeextensordigitorumbrevis.Thedeepperonealnerveinnervatesthemusclesofthe
anteriorcompartment,includingtibialisanterior,extensorhallucislongus,extensordigitorum
longus, peroneus tertius, and extensor digitorum brevis.63 The superficial peroneal nerve
innervatesperoneuslongus,peroneusbrevis, andperoneustertius.Itexitsthedeepfasciaof
the leg10to13cmproximal tothetipofthelateralmalleolusandremainssubcutaneous.It
thendividesintotheintermediateandmedialdorsalcutaneousnerves.Thesedivisionscarry
sensationfromtheanteriorlowerleganddorsumofthefoot.
TheTibialNerve
Thetibialnervepassesthroughthepoplitealfossabelowthearchofthesoleusmuscle.Within
thepoplitealfossa,itgivesoffbranchestothegastrocnemius,popliteus,soleus,andplantaris
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muscles,aswellastothesuralnerve.Distaltosoleus,thetibialnerveinnervatesthetibialis
posterior,flexor digitorum longus, andflexor hallucis longus muscles. Itpasses beneath the
medial malleolus,whereitisboundbythe flexorretinaculum inthe “tarsaltunnel.”Hereit
dividesintomedialandlateralplantarbranches.Themedialplantarnervepassesbeneaththe
insertionoftheabductorhallucisandthentravelswithinconnectivetissueattachingtheflexor
hallucisbrevistothetarsalbones.Itinnervatestheabductorhallucis,flexordigitorumbrevis,
flexor hallucis brevis muscles, as well as the first lumbrical. Sensation is carried from the
medialaspectofthesole,themedialthreeandone-halfdigits,andthenailbeds.Thelateral
plantar nerve courses deep tothe insertion oftheabductorhallucis,passingbetweenflexor
digitorumbrevis andquadratus plantae.Itinnervatesquadratusplantae,flexordigitiminimi,
adductorhallucis,allinterossei,thethreeremaininglumbricals,andtheabductordigitiminimi
muscles, and carries cutaneous sensation from the lateral sole and lateral one and one-half
digits. Both the medial and lateral plantar nerves divide into interdigital nerves located
beneath the transverse metatarsal ligament, terminating at the distal phalanges, and carry
sensation from the plantar surfaces and web spaces between the toes. The medial plantar
properdigitalnervesuppliestheskinonthemedialaspectofthefirstdigit.
Figures6-8and6-9providebothananteriorandposteriorviewoftheperonealandtibial
nervesaswellasthecorrespondingsofttissueandbonesoftheleg.
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FIGURE6-8.Theperonealandtibialnervesviewedanteriorlyinthelegrelativetoassociatedboneandsofttissue
(FromAgurAM,DalleyAF.Grant’sAtlasofAnatomy.13thed.Philadelphia,PA:WoltersKluwer;2012,with
permission).
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FIGURE6-9.Theperonealandtibialnervesviewedposteriorlyinthelegrelativetoassociatedboneandsofttissue
(FromAgurAM,DalleyAF.Grant’sAtlasofAnatomy.13thed.Philadelphia,PA:WoltersKluwer;2012,with
permission).
TheSuralNerve
The sural nerve originates from the tibial and commonperoneal nerves, carryingcutaneous
sensationfromthelateralaspectoftheankle,heel,andfourthandfifthdigits.Italsomediates
foot proprioception, measures stretch in the Achilles tendon, and provides sensation from
deeper tissues. Traditionally, thesuralnerve is considered a purelysensorynerve, although
electrophysiologicstudieshavedemonstratedmotorfibers.Figure6-10showsthepositionof
thesuralnerverelativetotheperonealandtibialnerves.
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DiagnosingNerveInjuryintheLegandFoot
Thehistoryshouldincludequestionsaboutthenatureoftheinjuryandanysensorychangeor
muscle weakness. Complaintsofburning pain, paresthesias, and numbnesssuggestinjury to
small diameter sensory fibers. Allodynia may be present. Dysfunction of large diameter
sensory fibers can cause proprioceptive loss and lead to ataxia, tremor, or disequilibrium.
Involvementofmotorfibersissuggestedbyweakness.Complaintsofdifficultywalkingora
changein appearanceofgait not explainedby painor limitedrange ofmotionshould raise
suspicionformotorinjury.Theneurologicexaminationshouldincludeevaluationofsensation,
motor function, reflexes, and gait. Abnormalities are more easily identified by comparison
with the unaffected limb. The sensory examination should include assessment of pain,
temperature,lighttouch,vibratorysensation,andproprioception.Appropriatemappingofthe
affected areas localizes to the corresponding nerve. Nerves can also be palpated and
percussedtoascertainthesiteofcompressionorentrapment.Elicitingmuscleweaknessisa
special challenge when examining patients with acute injuries, because many suffer from
severepain.Analgesicsmayfacilitatetheexamination.Inadditiontostrength,musclebulkand
tone are assessed. Chronicmotor nerveinjuryleads toatrophy. Weakjoints mayassume an
abnormalposition.Themusclesshouldbecloselyinspectedforsignsofdenervation,suchas
fasciculations or myokymia. The gait is often revealing. Patients with ankle dorsiflexion
weakness excessivelyflexthehip andknee when ambulating inorder toraisethe leg.This
compensationallowspassageofthepareticfootthroughtheswingphase.Lackofacontrolled
descent of the foot causes a characteristic slapping noise. The resulting appearance of the
patientattemptingtostepoveranobjecthasledtotheterm“steppagegait.”
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FIGURE6-10.Thesuralnerveanditsrelativepositiontothetibialandperonealnervesasitformsthem(FromAgur
AM,DalleyAF.Grant’sAtlasofAnatomy.13thed.Philadelphia,PA:WoltersKluwer;2012,withpermission).
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