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Lumbar plexusThe lumbar plexus is formed by the anterior rami of nerves L1 to L3, and most of the anterior ramus of L4 (Fig. 4.15and Table 4.!". #t also re$eives a $ontribution from the T1% (sub$ostal" nerve.

&ran$hes of the lumbar plexus in$lude the iliohypogastri$, ilio'inguinal, genitofemoral, lateral $utaneous nerve of thigh(lateral femoral $utaneous", femoral, and obturator nerves. The lumbar plexus forms in the substan$e of the psoasmaor mus$le anterior to its atta$hment to the transverse pro$esses of the lumbar vertebrae (Fig. 4.15)".

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Therefore, relative to the psoas maor mus$le, the various bran$hes emerge either*

anterior'genitofemoral nerve+

medial'obturator nerve+ or

lateral'iliohypogastri$, ilio'inguinal, and femoral nerves, and the lateral $utaneous nerve of the thigh.

Iliohypogastric and ilio-inguinal nerves (L1)

The iliohypogastri$ and ilio'inguinal nerves arise as a single trun from the anterior ramus of nerve L1 (Fig. 4.15".-ither before or soon after emerging from the lateral border of the psoas maor mus$le, this single trun divides intothe iliohypogastri$ and the ilio'inguinal nerves.

#liohypogastri$ nerve

The iliohypogastric nerve passes a$ross the anterior surfa$e of the uadratus lumborum mus$le, posterior to theidney. #t pier$es the transversus abdominis mus$le and $ontinues anteriorly around the body bet/een the transversusabdominis and internal obliue mus$les. 0bove the ilia$ $rest, a lateral cutaneous branch pier$es the internal andexternal obliue mus$les to supply the posterolateral gluteal sin (Fig. 4.15".

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The remaining part of the iliohypogastri$ nerve (the anterior $utaneous bran$h" $ontinues in an anterior dire$tion,pier$ing the internal obliue ust medial to the anterior superior ilia$ spine as it $ontinues in an obliuely do/n/ardand medial dire$tion. &e$oming $utaneous, ust above the super2$ial inguinal ring, after pier$ing the aponeurosis ofthe external obliue, it distributes to the sin in the pubi$ region (Fig. 4.15". Throughout its $ourse, it also suppliesbran$hes to the abdominal mus$ulature.

#lio'inguinal nerve

The ilio'inguinal nerve is smaller than, and inferior to, the iliohypogastri$ nerve as it $rosses the uadratus lumborummus$le. #ts $ourse is more obliue than that of the iliohypogastri$ nerve, and it usually $rosses part of the ilia$usmus$le on its /ay to the ilia$ $rest. ear the anterior end of the ilia$ $rest, it pier$es the transversus abdominismus$le, and then pier$es the internal obliue mus$le and enters the inguinal $anal.

The ilio'inguinal nerve emerges through the super2$ial inguinal ring, along /ith the spermati$ $ord, and provides$utaneous innervation to the upper medial thigh, the root of the penis, and the anterior surfa$e of the s$rotum in men,or the mons pubis and labium maus in /omen (Fig. 4.15". Throughout its $ourse, it also supplies bran$hes to theabdominal mus$ulature.

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Genitofemoral nerve (L1 and L2)

The genitofemoral nerve arises from the anterior rami of the nerves L1 and L% (Fig. 4.15". #t passes do/n/ard in thesubstan$e of the psoas maor mus$le until it emerges on the anterior surfa$e of psoas maor. #t then des$ends on thesurfa$e of the mus$le, in a retroperitoneal position, passing posterior to the ureter. #t eventually divides into genitaland femoral bran$hes.

The genital branch $ontinues do/n/ard and enters the inguinal $anal through the deep inguinal ring. #t $ontinuesthrough the $anal and*

in men, innervates the $remasteri$ mus$le and terminates on the sin in the upper anterior part of thes$rotum+ and

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in /omen, a$$ompanies the round ligament of the uterus and terminates on the sin of the mons pubis and

labium maus.

The femoral branch des$ends on the lateral side of the external ilia$ artery and passes posterior to the inguinalligament, entering the femoral sheath lateral to the femoral artery. #t pier$es the anterior layer of the femoral sheathand the fas$ia lata to supply the sin of the upper anterior thigh (Fig. 4.15".

Lateral cutaneous nerve of thigh (L2 and L3)The lateral $utaneous nerve of thigh arises from the anterior rami of nerves L% and L3 (Fig. 4.15". #t emerges from thelateral border of the psoas maor mus$le, passing obliuely do/n/ard a$ross the ilia$us mus$le to/ard the anteriorsuperior ilia$ spine (Fig. 4.15". #t passes posterior to the inguinal ligament and enters the thigh.

The lateral $utaneous nerve of thigh supplies the sin on the anterior and lateral thigh to the level of the nee (Fig.4.15".

Obturator nerve (L2 to L)

The obturator nerve arises from the anterior rami of the nerves L% to L4 (Fig. 4.15". #t des$ends in the psoas maormus$le, emerging from its medial side near the pelvi$ brim (Fig. 4.15)".

The obturator nerve $ontinues posterior to the $ommon ilia$ vessels, passes a$ross the lateral /all of the pelvi$ $avity,and enters the obturator $anal, through /hi$h the obturator nerve gains a$$ess to the medial $ompartment of the

thigh.

#n the area of the obturator $anal, the obturator nerve divides into anterior and posterior branches. n entering themedial $ompartment of the thigh, the t/o bran$hes are separated by theobturator externus and addu$tor brevismus$les. Throughout their $ourse through the medial$ompartment, these t/o bran$hes supply*

arti$ular bran$hes to the hip oint+

mus$ular bran$hes to obturator externus, pe$tineus, addu$tor longus, gra$ilis, addu$tor brevis, and addu$tor

magnus mus$les+

$utaneous bran$hes to the medial aspe$t of the thigh+ and

in asso$iation /ith the saphenous nerve, $utaneous bran$hes to the medial aspe$t of the upper part of the leg,and arti$ular bran$hes to the nee oint (Fig. 4.15".

!emoral nerve (L2 to L)

The femoral nerve arises from the anterior rami of nerves L% to L4 (Fig. 4.15". #t des$ends through the substan$e ofthe psoas maor mus$le, emerging from the lo/er lateral border of the psoas maor (Fig. 4.15)". ontinuing itsdes$ent, the femoral nerve lies bet/een the lateral border of the psoas maor and the anterior surfa$e of the ilia$usmus$le. #t is deep to the ilia$us fas$ia and lateral to the femoral artery as it passes posterior to the inguinal ligamentand enters the anterior $ompartment of the thigh. 6pon entering the thigh, it immediately divides into multiplebran$hes.

utaneous bran$hes of the femoral nerve in$lude*

medial and intermediate $utaneous nerves supplying the sin on the anterior surfa$e of the thigh+ and

the saphenous nerve supplying the sin on the medial surfa$e of the leg (Fig. 4.15".

7us$ular bran$hes innervate the ilia$us, pe$tineus, sartorius, re$tus femoris, vastus medialis, vastus intermedius, andvastus lateralis mus$les. 0rti$ular bran$hes supply the hip and nee oints.

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NervesSomatic plexuses"acral and coccygeal ple#uses

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The sa$ral and $o$$ygeal plexuses are situated on the posterolateral /all of the pelvi$ $avity and generally o$$ur inthe plane bet/een the mus$les and blood vessels. They are formed by the ventral rami of 81 to o, /ith a signi2$ant$ontribution from L4 and L5, /hi$h enter the pelvis from the lumbar plexus (Fig. 5.5". erves from these mainlysomati$ plexuses $ontribute to the innervation of the lo/er limb and mus$les of the pelvis and perineum. utaneousbran$hes supply sin over the medial side of the foot, the posterior aspe$t of the lo/er limb, and most of theperineum.

8a$ral plexus

The sa$ral plexus on ea$h side is formed by the anterior rami of 81 to 84, and the lumbosa$ral trun (L4 and L5" (Fig.5.!9". The plexus is formed in relation to the anterior surfa$e of the piriformis mus$le, /hi$h is part of theposterolateral pelvi$ /all. 8a$ral $ontributions to the plexus pass out of the anterior sa$ral foramina and $ourselaterally and inferiorly on the pelvi$ /all. The lumbosa$ral trun, $onsisting of part of the anterior ramus of L4 and allof the anterior ramus of L5, $ourses verti$ally into the pelvi$ $avity from the abdomen by passing immediately anteriorto the sa$ro'ilia$ oint.

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:ray rami $ommuni$antes from ganglia of the sympatheti$ trun $onne$t /ith ea$h of the anterior rami and $arrypostganglioni$ sympatheti$ 2bers destined for the periphery to the somati$ nerves (Fig. 5.!1". #n addition, spe$ialvis$eral nerves (pelvic splanchnic nerves" originating from 8% to 84 deliver preganglioni$ parasympatheti$ 2bers tothe pelvi$ part of the prevertebral plexus (Fig. 5.!%".

-a$h anterior ramus has ventral and dorsal divisions that $ombine /ith similar divisions from other levels to formterminal nerves (see Fig. 5.!9". The anterior ramus of 84 has only a ventral division.

&ran$hes of the sa$ral plexus in$lude the s$iati$ nerve and gluteal nerves, /hi$h are maor nerves of the lo/er limb,and the pudendal nerve, /hi$h is the nerve of the perineum (Table 5.4". umerous smaller bran$hes supply the pelvi$/all, ;oor, and lo/er limb.

7ost nerves originating from the sa$ral plexus leave the pelvi$ $avity by passing through the greater s$iati$ forameninferior to piriformis mus$le, and enter the gluteal region of the lo/er limb. ther nerves leave the pelvi$ $avity using

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di

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8$iati$ nerveThe sciatic nerve is the largest nerve of the body and $arries $ontributions from L4 to 83 (Figs. 5.5 and 5.!9". #t*

forms on the anterior surfa$e of the piriformis mus$le and leaves the pelvi$ $avity through the greater s$iati$foramen inferior to piriformis+

passes through the gluteal region into the thigh, /here it divides into its t/o maor bran$hes, the $ommon2bular nerve ($ommon peroneal nerve" and the tibial nerve'dorsal divisions of L4, L5, 81, and 8% are $arried inthe $ommon 2bular part of the nerve and the ventral divisions of L4, L5, 81, 8%, and 83 are $arried in the tibialpart+

innervates mus$les in the posterior $ompartment of the thigh and mus$les in the leg and foot+ and

$arries sensory 2bers from the sin of the foot and lateral leg.

=udendal nerve8% to 84 (Figs. 5.5 and 5.!9". #t*

leaves the pelvi$ $avity through the greater s$iati$ foramen, inferior to the piriformis mus$le, and enters thegluteal region+

$ourses into the perineum by immediately passing around the sa$rospinous ligament, /here the ligament oinsthe is$hial spine, and through the lesser s$iati$ foramen (this $ourse taes the nerve out of the pelvi$ $avity,around the peripheral atta$hment of the pelvi$ ;oor, and into the perineum"+

is a$$ompanied throughout its $ourse by the internal pudendal vessels+ and

innervates sin and seletal mus$les of the perineum, in$luding the external anal and external urethralsphin$ters.

ther bran$hes of the sa$ral plexus

ther bran$hes of the sa$ral plexus in$lude*

motor bran$hes to mus$les of the gluteal region, pelvi$ /all, and pelvi$ ;oor (superior and inferior glutealnerves, nerve to obturator internus and superior gemellus, nerve to uadratus femoris and inferior gemellus,nerve to piriformis, nerves to levator ani"+ and

sensory nerves to sin over the inferior gluteal region and posterior aspe$ts of the thigh and upper leg(perforating $utaneous nerve and posterior cutaneous nerve of the thigh" (Figs. 5.5 and 5.!9".

The superior gluteal nerve, formed by bran$hes from the dorsal divisions of L4 to 81, leaves the pelvi$ $avity

through the greater s$iati$ foramen superior to piriformis mus$le and supplies mus$les in the gluteal region'gluteusmedius, gluteus minimus, and tensor fasciae latae (tensor offascia lata" muscles.

The inferior gluteal nerve, formed by bran$hes from the dorsal divisions of L5 to 8%, leaves the pelvi$ $avity throughthe greater s$iati$ foramen inferior to the piriformis mus$le and supplies the gluteus maximus, the largest mus$le inthe gluteal region.

&oth superior and inferior gluteal nerves are a$$ompanied by $orresponding arteries.

The nerve to the obturator internus and the asso$iated superior gemellus mus$le originates from the ventraldivisions of L5 to 8% and leaves the pelvi$ $avity through the greater s$iati$ foramen inferior to the piriformis mus$le.Lie the pudendal nerve, it passes around the is$hial spine and through the lesser s$iati$ foramen to enter theperineum and supply the obturator internus mus$le from the medial side of the mus$le, inferior to the atta$hment ofthe levator ani mus$le.

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The nerve to the quadratus femoris mus$le and the inferior gemellus mus$le, and the posterior cutaneousnerve of the thigh (posterior femoral cutaneous nerve" also leave the pelvi$ $avity through the greater s$iati$foramen inferior to the piriformis mus$le and $ourse to mus$les and sin, respe$tively, in the lo/er limb.

6nlie most of the other nerves originating from the sa$ral plexus, /hi$h leave the pelvi$ $avity through the greaters$iati$ foramen either above or belo/ the piriformis mus$le, the perforating cutaneous nerve leaves the pelvi$$avity by penetrating dire$tly through the sa$rotuberousligament and then $ourses to sin over the inferior aspe$t ofthe butto$s.

The nerve to the piriformis and a number of small nerves to the levator ani and $o$$ygeus mus$les originate fromthe sa$ral plexus and pass dire$tly into their target mus$les /ithout leaving the pelvi$ $avity.

The obturator nerve (L% to L4" is a bran$h of the lumbar plexus. #t passes inferiorly along the posterior abdominal/all /ithin the psoas mus$le, emerges from the medial surfa$e of the psoas, passes posteriorly to the $ommon ilia$artery and medially to the internal artery at the pelvi$ inlet, and then $ourses along the lateral pelvi$ /all. #t leaves thepelvi$ $avity by traveling through the obturator $anal and supplies the addu$tor region of the thigh.

o$$ygeal plexus

The small $o$$ygeal plexus has a minor $ontribution from 84 and is formed mainly by the anterior rami of 85 and o,/hi$h originate inferiorly to the pelvi$ ;oor. They penetrate the $o$$ygeus mus$le to enter the pelvi$ $avity and oin/ith the anterior ramus of 84 to form a single trun, from /hi$h small anococcygeal nerves originate (Table 5.4".These nerves penetrate the mus$le and the overlying sa$rospinous and sa$rotuberous ligaments and pass super2$ially

to innervate sin in the anal triangle of the perineum.

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