5.22 Summary of Lumbar & Sacral Plexuses

Lumbar Plexus Summary (463-4)

Anterior rami L1-4 supply psoas and QL segmentally then form plexus in substance of psoas.

Innervates part of lower abdominal wall, but mainly for lower limb

-           reinforces sacral plexus (main plexus of lower limb)

L1 IH an II

L1,2 GF

L2,3 (posterior divisions) lat fem cut

L2,3,4 (posterior divisions) femoral

L2,3,4 (anterior divisions) obturator


II and IH

Really segmental body wall nerve and its collateral branch in series with thoracic nerves

skin over inguinal region

motor supply to fibres of internal oblique and transversus roofing the inguinal canal

reach conjoint tendon


Femoral part skin below middle of inguinal ligament

Genital part abdominal wall herniated into scrotum for testicular descent (cord)

-           sensory to tunica vaginalis and spermatic fasciae

-           motor to cremaster; supplies small area of anterior scrotal and labial skin.

Lateral Femoral Cutaneous Nerve

Wholly sensory iliac fascia and peritoneum of iliac fossa

lateral side of thigh to knee

-           emerges from lateral border of psoas and enters thigh through / under inguinal ligament

Femoral Nerve (464, 466-7)

Lateral border of psoas across iliac fossa b/n psoas and iliacus deep to fascia

supplies iliacus in abdomen

-           passes beneath inguinal ligament lateral to femoral sheath, enters femoral triangle

-           pectineus and breaks up into several branches.

N to pectineus behind sheath to that muscle

N to sartorius may pierce that muscle and continue as:

Intermediate femoral cutaneous nerve skin and fascia lata to knee

Medial fem cut nerve medial side of thigh; anterior branch reaches front of knee

N to rectus femoris doubled; branch also hip jt

N to vastus lateralis: with desc. branch of lat fem circumflex artery b/n rectus fem and vastus int.

N to vastus intermedius muscle

N to vastus medialis enters upper subsartorial canal to muscle

-           nerves to the three vasti also knee

Saphenous nerve in front of femoral artery in subsartorial canal

infrapatellar branch: pierces sartorius to patella plexus

-           then pierces fascia lata b/n sartorius and gracilis skin and periosteum over subcut tibia

-           runs with great saphenous vein in front of medial malleolus medial foot short of big toe.

Obturator Nerve (467)

From medial psoas on ala on sacrum lateral to lumbosacral trunk

down to side wall of pelvis b/n origin of internal iliac artery and ilium to obturator foramen

supplies parietal peritoneum on pelvic side wall (next to ovary)

Then splits into ant and post divisions:

Anterior over obturator externus thigh, hip jt

-           runs over adductor brevis deep to pectineus and adductor longus

-           supplies these two adductors and maybe pectineus, also gracilis

-           cutaneous branch medial side of thigh

Posterior obturator externus; pierces its upper border thigh deep to adductor brevis

-           runs on adductor magnus (supplies it)

-           branch with femoral artery to popliteal fossa knee jt.

Sacral Plexus (465)

Formed from lumbosacral trunk (L4,5) and upper four anterior sacral rami

-           the rami divide and unite as they converge on greater sciatic foramen.

Nerve to Piriformis

S1,2 Straight to muscle

Perforating Cutaneous Nerve

S2,3 Pierces sacrotuberous ligament and glut max there skin on lower medial buttock

Posterior fem cut nerve (469, 504)

S1,2,3 Below piriformis on sciatic lower border of glut max gastroc bellies

strip of deep fascia and skin b/n anterior and posterior axial lines from buttock to midcalf

gluteal branches to buttock

perineal branch around hamstrings & gracilis lat part of posterior 2/3 of scrotum / labium majora

Pelvic Splanchnics

S2,3,4 PNS outflow; join inferior hypogastric plexus

motor to bladder and colon from splenic flexure down and cause erection

afferents include those for distension, pain from bladder, lower cervix and colon and rectum

referred pain felt in femoral cutaneous nerve distribution

Pudendal Nerve

S2,3,4; curls round gluteal surface of sacrospinous lig to pudendal canal pelvic floor & perineum

inferior rectal nerve arches through ischioanal fossa fat to EAS, canal and perianal skin

perineal nerve terminal branch forward to skin of posterior 2/3 of scrotum / vulva

-           and mucous membrane of urethra and vagina

-           motor to perineal muscles (ischiocavernous, bulbospongiosus, superior and deep transverse perinei and sphincter urethrae)

dorsal nerve of penis / clitoris (other terminal branch) pierces perineal membrane below s. pubis.

Muscular Branches of S3,4

levator ani and coccygeus (upper surfaces)

Perineal Branch of S4

B/n levator ani and coccygeus sin over ischioanal fossa

N to Quadratus Femoris (469)

L4,5,S1 on ischium deep to sciatic runs deep to obturator internus deep surface of quadratus fem

-           also supplies inferior gemellus and hip jt branch

Nerve to obturator internus (469)

L5,S1,2; below piriformis, curls around base of ischial spine obturator internus

-           also superior gemellus

Superior gluteal nerve (469)

L4,5,S1Passes back though greater sciatic notch above piriformis plane b/n glut med and minimus

supplies both and ends in tensor fasciae latae

Inferior gluteal nerve (469)

L5,S1,2 Back below piriformis deep surface of glut maximus

Sciatic Nerve


Largest branch; actually union of tibial and common peroneal parts

Passes to buttock on post surface of ischium (n. to quadratus femoris deep, post fem cut n. superficial)

-           from midway b/n greater trochanter and ischial tuberosity hamstring compartment

-           on obturator internus and gamelli, quadratus femoris then adductor magnus

-           overlaid by long head biceps

Main trunk hamstrings, ischial fibres of adductor magnus

Then divides tibial and common peroneal nerves

Branches for long head of biceps and two semi muscles are from tibial part, branch to short head biceps from common peroneal part.

Common Peroneal Nerve (L4,5,S1,2)

Supplies extensor and peroneal compartments of leg and dorsum of foot

Enters apex of popliteal fossa medial to biceps tendon under deep fascia

crosses plantaris, lat head gastroc around neck of fibula (injured here) through peroneus longus

divides; in itself supplies no muscles but 3 articular and 2 cutaneous branches:

-           articular branches (upper, lower lateral and recurrent genicular) knee

-           sural communicating nerve sural nerve below gastroc heads to skin

-           lat cut nerve of calf skin and deep fascia over upper half of peroneal compartment

Deep peroneal nerve

Formed in peroneus longus deep to EDL interosseus membrane lateral to vessels

crosses lower end of tibia dorsum of foot skin of first cleft

Muscles = extensor compartment; EDL, TA, EHL, peroneus tertius

-           and lateral branch in foot and extensor digitorum brevis

Superficial peroneal nerve

In substance of peroneus longus in that muscle to anterior border ~1/3 way down leg

-           and perforates the fascia to supply skin over peronei and extensor muscles in lower third of leg

Divides to medial and lateral branches to skin and deep fascia on dorsum of foot

-           medial branch medial side of big toe and second cleft

-           lateral branch third and fourth clefts

Tibial Nerve (L4,5,S1,2,3)

Calf and sole to toenails; enters apex of popliteal fossa midline of limb deep to gastroc heads

across popliteus runs beneath fibrous arch of soleus

Three branches in popliteal fossa:

Three genicular nerves: upper and lower medial and middle

Five muscular branches: plantaris, heads of gastroc, soleus, popliteus

One cutaneous: sural nerve pierces fascia halfway down leg

-           joined by peroneal communicating nerve

-           runs down beside small saphenous vein behind lateral malleolus lateral little tow

From fibrous arch nerve runs down with posterior tibial vessels deep to soleus

-           neurovascular bundle in groove b/n bellies of FHL and FDL

-           Behind medial malleolus (beneath retinaculum) divides:

Branches in calf

Four muscular branches:  soleus, tib posterior, FH and FDL

Median calcaneal: pierces retinaculum weight bearing skin of heal.

Medial and lateral plantar nerves correspond to median and ulnar nerves