Lumbosacral Plexus B&B

Question 1

the lumbar and sacral plexus are made of which nerve roots, respectively?

Answer 1

lumbar: T12 - L4, supplies skin and muscles of lower limb

sacral: L4 - S4, supplies skin and muscles of pelvis and lower limb

Question 2

from which nerve roots is the iliohypogastric nerve derived, and what is its function?

Answer 2

T12 - L1

motor: internal oblique and transverse abdominis

sensory: suprapubic (hypogastric) region - below umbilicus, above pubic bone

Question 3

This nerve, derived from nerve roots T12 - L1, provides motor input to the internal oblique and transverse abdominis. What sensory innervation does this nerve also provide?

Answer 3

iliohypogastric nerve

motor: internal oblique and transverse abdominis

sensory: suprapubic (hypogastric) region - below umbilicus, above pubic bone

Question 4

During abdominal and pelvic surgeries such as laparoscopic surgeries, hernia surgeries, and hysterectomies, transverse incisions are made. At the close of the surgery, sutures may trap this nerve, cause burning pain or paresthesia that radiates from the incision to the suprapubic area. What nerve is this?

Answer 4

iliohypogastric nerve

motor: internal oblique and transverse abdominis

sensory: suprapubic (hypogastric) region - below umbilicus, above pubic bone

commonly injured in abdominal/pelvic surgery

Question 5

from which nerve roots is the genitofemoral nerve derived, and what is its function?

Answer 5

L1-L2

motor: cremasteric muscle (males, covers testis and spermatic cord)

sensory: genital branch and femoral branch (skin of upper anterior thigh)

Question 6

This nerve, derived from L1 and L2, provides motor input to the cremasteric muscle in males. It has 2 sensory branches. What is?

Answer 6

genitofemoral nerve

motor: cremasteric muscle - covers testis and spermatic cord

sensory genital branch: skin of anterior scrotum (males), skin over mons pubis and labia majora (females)

sensory femoral branch: skin of upper anterior thigh

Question 7

what is the consequence of injury to the genitofemoral nerve, as may occur by retractor blades in abdominal surgery?

Answer 7

absent cremasteric reflex + decreased sensation of anterior thigh, decreased sensation of labia/scrotum

motor: cremasteric muscle

sensory: genital and femoral branches

Question 8

from which nerve roots is the lateral femoral cutaneous nerve derived, and what is its function?

Answer 8

L2 - L3

purely sensory to lateral thigh

courses under inguinal ligament into thigh (susceptible to compression by tight clothing, obesity, pregnancy)

Question 9

meralgia paresthetica is a consequence of compression of which nerve?

Answer 9

lateral femoral cutaneous nerve (L2 - L3), purely sensory to lateral thigh

courses under inguinal ligament into thigh - susceptible to compression by tight clothing, obesity, pregnancy

meralgia paresthetica: outer thigh nerve syndrome with burning pain and paresthesia

Question 10

from which nerve roots is the obturator nerve derived, and what is its function?

Answer 10

L2 - L4

obturare = “to close”
closes / adducts thigh

motor: adductor longus, adductor brevis, adductor magnus, gracilis, obturator externus

sensory: medial thigh

Question 11

This nerve, derived from L2-L4 nerve roots, innervates the thigh adductors, including the adductor longus, adductor brevis, adductor magnus, gracilis, and obturator externus. What is?

Answer 11

obturator nerve: L2 - L4

obturare = “to close”
closes / adducts thigh

motor: adductor longus, adductor brevis, adductor magnus, gracilis, obturator externus

sensory: medial thigh

Question 12

What would be the consequence of injury to the obturator nerve, as which sometimes occurs during surgery via a trocar pushed too far into the posterior pelvis?

Answer 12

weak adduction + numbness o medial thigh

L2 - L4
obturare = “to close”
motor: adductors
sensory: medial thigh

Question 13

from which nerve roots is the femoral nerve derived, and which anterior thigh muscles does it innervate?

Answer 13

L2 - L4

innervates:
hip flexors- pectineus, iliacus (part of iliopsoas), sartorius
knee extensors - quadriceps femoris (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius)

Question 14

from which nerve roots is the femoral nerve derived, and which sensory branches does it give off to innervate the medial thigh and lower leg? (2)

Answer 14

L2 - L4

1. anterior cutaneous branches: skin of anteromedial thigh
2. saphenous nerve: skin of medial leg and foot

Question 15

the saphenous nerve innervates the skin on the medial leg and foot and is a branch of the _____ nerve, derived from ______ nerve roots

Answer 15

femoral nerve: L2 - L4

Question 16

During CABG procedures, this vein is often stripped, often causing damage to the accompanying nerve, which results in numbness of the lower leg. What is?

Answer 16

saphenous vein stripping - may damage saphenous nerve (branch of femoral nerve)

Question 17

how can the femoral nerve be located correctly to perform a femoral nerve block?

Answer 17

femoral vessels are located at the groin in this order from lateral to medial: femoral nerve, femoral artery, femoral vein, lymph (NAVL)

palpate the femoral artery because it is easiest to find, then inject laterally to the artery

Question 18

weakness or absence of the patellar reflex = injury to the _____ nerve

Answer 18

femoral nerve (L2 - L4): innervates hip flexors and knee extensors

injury —> weak flexion of thigh and extension at knee

[patellar reflex requires extension at knee]

Question 19

from which nerve roots does the sciatic nerve derive, and what are its 2 branches?

Answer 19

L4 - S3, largest nerve in the body (2cm wide!), motor and sensory

branches:
1. common peroneal
2. tibial

Question 20

what are the 2 motor branches of the common peroneal nerve (branch of sciatic nerve) and their functions?

Answer 20

common peroneal nerve: motor/sensory to lower leg + dorsum of foot

1. superficial fibular nerve: muscles of lower lateral leg (fibularis longus + brevis), everts foot
2. deep fibular nerve: muscles of anterior lower leg, dorsiflexion of foot, extension of toes

Question 21

sensory innervation to the dorsum of the foot is supplied by:

Answer 21

common peroneal nerve (branch of sciatic nerve, L4-S3)

Question 22

the superficial and deep fibular nerves are branches of the ______, which is a branch of the ______, which is derived from nerve roots ________

Answer 22

sciatic nerve (L4-S3) —>

common peroneal nerve (+ tibial nerve) —>

superficial and deep fibular nerves

Question 23

how can the common peroneal nerve become injured and what are the symptoms and signs?

Answer 23

peroneal = fibula, wraps around fibula below knee (branch of sciatic nerve)

injured by prolonged lying (bed rest), leg casts, fibular neck fractures

symptoms - foot drop (weak dorsiflexion), limp foot (tripping), sensory loss of lateral shin

Question 24

A patient has been on bed rest following a major surgery. At one week, they are visited by the physical therapist to begin walking again. Upon trying to walk, the patient continues to trip, and there is noticeable foot drop. Upon PE, it is found that there is loss of sensation to the dorsum foot and lateral shin. Which nerve is affected?

Answer 24

common peroneal nerve (branch of sciatic nerve, L4-S3)

motor/sensory to lower leg and dorsum of foot (via superficial and deep fibular branches)

foot drop due to weak dorsiflexion

Question 25

the _____ nerve is a branch of the sciatic nerve and travels under the medial malleolus, through the tarsal tunnel, to supply sensory innervation to the heel and sole of the foot

Answer 25

the TIBIAL nerve is a branch of the sciatic nerve (L4-S3) and travels under the medial malleolus, through the tarsal tunnel, to supply sensory innervation to the heel and sole of the foot

Question 26

what are the actions of the posterior leg muscles supplied by the tibial nerve (branch of sciatic nerve)? (3)

Answer 26

1. plantar flexion
2. toe flexion
3. inversion of foot (turning it in)

these include: popliteus, flexor hallucis longus, flexor digitorum longus, tibialis posterior, plantaris, soleus, gastrocnemius

Question 27

which nerve is most likely to be injured by tarsal tunnel narrowing or a large Baker’s cyst?

Answer 27

tibial nerve (branch of sciatic, L4-S3): supplies motor innervation to posterior leg muscles and sensory innervation to heel and sole of foot

travels through tarsal tunnel to follow back of leg

injury —> burning/numbness on sole of foot, loss of plantar flexion/toe flexion/foot inversion

Question 28

from which nerve roots is the pudendal nerve derived, and what is its function?

Answer 28

S2-S4

motor/sensory innervation of genital area

Question 29

pain with sitting and incontinence following vaginal childbirth are due to damage to the _____ nerve

Answer 29

pudendal nerve: S2-S4

motor/sensory innervation of genital area