Fall_25_Lumbar+Sacral_Plexus

Question 1

Which spinal nerves form the lumbar plexus?

Answer 1

Ventral rami of L1 to L4 (sometimes T12 contribution).

The plexus lies within the psoas major muscle and supplies the anterior and medial thigh.

Question 2

Where is the lumbar plexus located anatomically?

Answer 2

Within the posterior part of the psoas major muscle.

It forms in the posterior third of psoas, between its fascial planes, deep to the fascia transversalis.

Question 3

Which major branches arise from the lumbar plexus?

Answer 3

Iliohypogastric, ilioinguinal, genitofemoral, lateral femoral cutaneous, femoral, and obturator nerves.

These branches supply abdominal wall, groin, and lower limb structures.

Question 4

What is the primary motor function of the lumbar plexus?

Answer 4

Innervation of anterior and medial thigh muscles for hip flexion and knee extension.

Femoral and obturator nerves provide motor control for these movements.

Question 5

What is the sensory distribution of the lumbar plexus?

Answer 5

Anterior and medial thigh, lower abdominal wall, and part of medial leg via saphenous branch.

Femoral and cutaneous branches supply these regions.

Question 6

What are the roots of the iliohypogastric and ilioinguinal nerves?

Answer 6

L1 (sometimes T12 contribution).

They emerge from the lateral border of psoas and traverse obliquely across the quadratus lumborum.

Question 7

What is the clinical relevance of the ilioinguinal nerve?

Answer 7

It provides sensory innervation to the groin and upper medial thigh and is often targeted in hernia repair anesthesia.

Infiltration along the inguinal canal reduces postoperative pain for hernia repair or orchiectomy.

Question 8

What are the roots of the genitofemoral nerve?

Answer 8

L1–L2.

It pierces the psoas muscle anteriorly and divides into genital and femoral branches.

Question 9

What area does the genital branch of the genitofemoral nerve supply?

Answer 9

Cremaster muscle and skin of the scrotum or mons pubis.

It provides both motor and sensory fibers relevant to cremasteric reflex.

Question 10

What area does the femoral branch of the genitofemoral nerve supply?

Answer 10

Skin over the femoral triangle.

Purely sensory branch contributing to upper anterior thigh sensation.

Question 11

What are the roots of the lateral femoral cutaneous nerve (LFCN)?

Answer 11

L2–L3.

It passes under or through the inguinal ligament near the ASIS to supply anterolateral thigh skin.

Question 12

What is meralgia paresthetica?

Answer 12

Entrapment of the lateral femoral cutaneous nerve under the inguinal ligament.

Presents as burning or numbness over the lateral thigh; common in obesity, tight belts, or pregnancy.

Question 13

What are the roots of the femoral nerve?

Answer 13

L2–L4 posterior divisions.

Largest branch of the lumbar plexus; descends between psoas and iliacus to the thigh.

Question 14

What muscles does the femoral nerve innervate?

Answer 14

Quadriceps femoris, sartorius, pectineus, and iliacus.

These muscles produce hip flexion and knee extension.

Question 15

What is the sensory territory of the femoral nerve?

Answer 15

Anterior thigh and medial leg via the saphenous nerve.

Saphenous is its terminal sensory branch continuing below the knee.

Question 16

What are the roots of the obturator nerve?

Answer 16

L2–L4 anterior divisions.

It descends medial to psoas and exits through the obturator foramen to the medial thigh.

Question 17

What muscles does the obturator nerve supply?

Answer 17

Adductor longus, brevis, magnus (part), gracilis, and obturator externus.

Responsible for thigh adduction and assists in hip stabilization.

Question 18

What is a common surgical risk related to the obturator nerve?

Answer 18

Stimulation and adductor spasm during transurethral resection of the bladder.

The nerve lies close to the bladder wall and may require an obturator block to prevent this reflex.

Question 19

Which spinal nerves form the sacral plexus?

Answer 19

L4–S4 ventral rami.

It lies on the anterior surface of the piriformis muscle and supplies posterior thigh, leg, and perineum.

Question 20

What are the main terminal branches of the sacral plexus?

Answer 20

Sciatic and pudendal nerves.

Other branches include superior/inferior gluteal, posterior femoral cutaneous, and small muscular branches.

Question 21

Which structure joins L4 and L5 to form the lumbosacral trunk?

Answer 21

A descending branch of L4 and the anterior ramus of L5.

This trunk connects lumbar and sacral plexuses, contributing to the sciatic nerve.

Question 22

What are the roots of the sciatic nerve?

Answer 22

L4–S3.

The largest nerve in the body; formed from both tibial (anterior) and common fibular (posterior) divisions.

Question 23

What muscles are innervated by the sciatic nerve before it divides?

Answer 23

Hamstring muscles and adductor magnus (part).

It provides posterior thigh motor function before dividing at or above the popliteal fossa.

Question 24

Where does the sciatic nerve divide into tibial and common fibular branches?

Answer 24

Usually near the apex of the popliteal fossa.

Division point is variable, occasionally occurring high in the pelvis.

Question 25

What is the clinical significance of the sciatic nerve?

Answer 25

Target for sciatic nerve block used for leg and foot surgery. It must be blocked proximal to its bifurcation for full coverage.

Question 26

What are the roots of the pudendal nerve?

Answer 26

S2–S4. Provides motor to external anal sphincter and perineal muscles, sensory to genitalia.

Question 27

What is a pudendal nerve block used for?

Answer 27

Perineal and obstetric analgesia. It anesthetizes perineum, external genitalia, and lower vagina during labor or episiotomy.

Question 28

Which dermatomes correspond to the anterior thigh?

Answer 28

L2–L3. Anterior cutaneous branches of femoral nerve supply these regions.

Question 29

Which dermatomes correspond to the medial leg and ankle?

Answer 29

L4. Transmitted by the saphenous branch of femoral nerve.

Question 30

Which dermatomes correspond to the dorsum of foot and big toe?

Answer 30

L5. Primarily supplied by superficial peroneal and deep peroneal nerves.

Question 31

Which dermatomes correspond to the lateral foot and sole?

Answer 31

S1. Served by sural and tibial branches.

Question 32

What are the main myotomes responsible for knee extension?

Answer 32

L3–L4. Femoral nerve and quadriceps group produce knee extension.

Question 33

Which myotomes control ankle plantarflexion?

Answer 33

S1–S2. Innervation from tibial nerve to gastrocnemius and soleus.

Question 34

Which myotomes control ankle dorsiflexion?

Answer 34

L4–L5. Supplied by the deep peroneal nerve to tibialis anterior.

Question 35

Where is local anesthetic deposited for a lumbar plexus (psoas compartment) block?

Answer 35

Within the fascial plane of the psoas major muscle posteriorly. Targets the lumbar plexus between psoas and quadratus lumborum for femoral, obturator, and LFCN coverage.

Question 36

What are key landmarks for lumbar plexus block using landmark technique?

Answer 36

Line from midline spinous process to iliac crest; needle inserted 4 cm lateral to L4 spinous process. Insertion depth 6–8 cm typically yields quadriceps twitch indicating proximity to plexus.

Question 37

What is the most common motor response confirming correct lumbar plexus block placement?

Answer 37

Quadriceps or patellar twitch. Indicates femoral nerve stimulation and proximity to the plexus within psoas.

Question 38

What are main risks of lumbar plexus block?

Answer 38

Epidural spread, renal or vascular puncture, and retroperitoneal hematoma. Deep block near major vessels and neuraxis increases complication risk.

Question 39

Where is local anesthetic injected for a femoral nerve block?

Answer 39

Lateral to the femoral artery, deep to fascia iliaca. This targets the nerve beneath fascia iliaca at the inguinal crease.

Question 40

What is the usual volume for femoral nerve block?

Answer 40

15–20 mL. Adequate to spread beneath fascia iliaca and surround the femoral nerve for surgical anesthesia.

Question 41

What motor response confirms correct femoral nerve block placement?

Answer 41

Quadriceps contraction or patellar snap. Indicates femoral nerve stimulation.

Question 42

What is a clinical indication for femoral nerve block?

Answer 42

Analgesia for femur or knee surgery and postoperative pain control after total knee arthroplasty. Provides effective anterior thigh and knee analgesia.

Question 43

What is the goal of fascia iliaca block?

Answer 43

Spread local anesthetic beneath fascia iliaca to block femoral, lateral femoral cutaneous, and obturator nerves. Large volume (30–40 mL) is used to ensure cephalad and lateral spread under the fascia.

Question 44

How is correct placement of local anesthetic confirmed in fascia iliaca block?

Answer 44

Hydrodissection showing separation of fascia iliaca from iliacus muscle. Visualizing spread under fascia confirms successful plane injection.

Question 45

What is the purpose of an obturator nerve block?

Answer 45

Prevent adductor spasm during transurethral bladder surgery. Blocks adductor longus, brevis, magnus, and external obturator motor branches.

Question 46

Where is local anesthetic deposited for obturator block?

Answer 46

Between adductor longus and adductor brevis or between brevis and magnus. Ultrasound guidance improves accuracy and reduces vascular puncture risk.

Question 47

What approaches are used for sciatic nerve block?

Answer 47

Posterior (classic Labat), subgluteal, and popliteal approaches. Choice depends on surgical site; posterior covers proximal thigh, popliteal covers distal leg and foot.

Question 48

What motor response confirms correct sciatic block placement?

Answer 48

Foot or toe movement (plantarflexion/dorsiflexion). Confirms proximity to tibial and peroneal components.

Question 49

What volume is used for sciatic nerve block?

Answer 49

20–25 mL. Sufficient to surround both divisions before or after bifurcation.

Question 50

What is the purpose of a saphenous nerve block?

Answer 50

Provide anesthesia to the medial leg and ankle. Used with popliteal sciatic block for complete lower leg coverage.

Question 51

Where is local anesthetic deposited for a saphenous block?

Answer 51

Subcutaneous ring around the medial tibial surface near the knee or ankle. Covers saphenous branch of femoral nerve supplying medial skin.

Question 52

What is the key advantage of a popliteal block?

Answer 52

Allows anesthesia of the foot while preserving hamstring function. The sciatic nerve is blocked distal to branches to hamstrings.

Question 53

Which structures are visualized in popliteal block under ultrasound?

Answer 53

Tibial and common peroneal nerves adjacent to popliteal artery and vein. These nerves appear as two hyperechoic ovals just above the fossa apex.

Question 54

Which combination of blocks provides complete anesthesia for lower leg surgery?

Answer 54

Femoral (or saphenous) + sciatic (popliteal) blocks. Covers all distal sensory and motor territories below the knee.

Question 55

Why should large volumes in deep blocks like lumbar plexus be avoided in anticoagulated patients?

Answer 55

Risk of retroperitoneal hematoma and compressive neuropathy. Anticoagulation increases bleeding risk in confined retroperitoneal space.

Question 56

Which block carries the highest risk of epidural spread?

Answer 56

Lumbar plexus (psoas compartment) block. Close proximity to neuraxis allows inadvertent spread into epidural space.