Lower Limb: Nerves

Question 1

What are the 2 plexi associated with the LL?

Answer 1

Lumbar and sacral plexus

Question 2

What spinal nerves make up the lumbar plexus & where is it formed?

Answer 2

ventral (anterior) rami of L1 - L4 combine WITHIN psoas major to form lumbar plexus
Peripheral nerves emerge from psoas

Question 3

What forms the sacral plexus and where is it formed?

Answer 3

The remaining part of ventral rami of L4 + ventral rami of L5 combine to form the lumbosacral trunk.
Lumbosacral trunk + ventral rami of S1-S3 and a bit of S4 combine to form the sacral plexus
Formation is ON piriformis, on the posterior wall of the pelvis

Question 4

What is the main nerves of the gluteal region?

Answer 4

Superior + inferior gluteal nerve (SP)

Question 5

What is the main nerve of the anterior compartment of thigh?

Answer 5

Femoral nerve (LP)

Question 6

What is the main nerve of the medial compartment of thigh?

Answer 6

Obturator nerve (LP)

Question 7

What is the main nerve of the posterior compartment of thigh?

Answer 7

Sciatic (SP)

Question 8

What is the main nerve of the anterior compartment of Leg?

Answer 8

Deep fibular (terminal of sciatic)

Question 9

What is the main nerve of the lateral compartment of Leg?

Answer 9

Superficial fibular (terminal of sciatic)

Question 10

What is the main nerve of the posterior compartment of Leg?

Answer 10

Tibial nerve (terminal of sciatic)

Question 11

What peripheral nerves emerge from the lateral border of psoas major?

Answer 11

L) L I I F

Ilioinguinal & iliohypogastric
Lateral cutanenous nerve of thigh
Femoral nerve

Question 12

What peripheral nerves emerge from the anterior and medial borders of psoas major?

Answer 12

Anterior - genitofemoral
Medial - obturator

‘Get Amongst My Ovaries’

Question 13

What is the course, spinal contribution and supply of the iliohypogastric & ilioinguinal nerves?

Answer 13

L1

Arise from the lateral border of psoas major onto QUADRATUS LOMBORUM

Motor - muscles of Ant abdo wall
Damage in old appendectomy could lead to inability to close inguinal canal - indirect hernia

Cutaneous - anteromedial part of upper thigh

Question 14

What is the course, spinal contribution and supply of the genitofemoral nerve?

Answer 14

L1, L2

Arise from anterior border of psoas major

Motor (genital branch) - spermatic cord

Cutaeneous (femoral branch) - skin immediately beneath inguinal ligament

Question 15

What is the course, spinal contribution and supply of the lateral cutaneous nerve?

Answer 15

L2, L3

Emerges from lateral border of psoas onto ILIACUS
Goes underneath the inguinal canal and drops into the anterior compartment of the thigh

Cutaneous - Skin of lateral thigh

Pregnancy & obesity - can get compressed against ASIS causing pins & needles

Question 16

What is the course, spinal contribution and supply of the femoral nerve?

Answer 16

Posterior fibres of L2 - L4

Emerges from lateral border of psoas and goes beneath the inguinal ligament, passing through femoral triangle (adjacent to femoral sheath)
Divides into anterior & posterior terminal branches 2.5cm below inguinal ligament

Nerve of anterior compartment of thigh (except iliopsoas as it gets rami fibres)

Motor - sartorius & quadriceps

Sensory - anteromedial part of thigh (anterior cutaneous nerve) and medial part of knee, leg & ankle (saphenous nerve) + articular branches to hip & knee joints

Question 17

What is the course, spinal contribution and supply of the obturator nerve?

Answer 17

Anterior fibres of L2 - L4
Nerve of medial compartment of thigh

Emerges from medial aspect of psoas and drops onto lateral wall of the pelvis, passing through the obturator canal and into medial compartment of thigh

Motor - 3 Adductors (- hamstring part of AM), pectineus, gracilis
Anterior & posterior divisions emerge between the 3 named adductors

Sensory - inferomedial skin of thigh + skin overlying hip joint

Question 18

What are the peripheral branches of the sacral plexus?

Answer 18

A bit of L4, L5 + S1 - S3
Superior + inferior gluteal nerves
Posterior cutaneous nerve of the thigh
Sciatic nerve

Question 19

What does the superior gluteal nerve innervate & what are its spinal routes?

Answer 19

Gluteus minimus + medius
L4 - S1
Emerges above piriformis

Question 20

What does the inferior gluteal nerve innervate & what are its spinal routes?

Answer 20

Gluteus maximus
L5 - S2
Arises below piriformis

Question 21

What does the posterior cutaneous nerve of the thigh innervate & what are its spinal routes?

Answer 21

S1 - S3

Skin over posterior aspect of thigh

Question 22

What is the course of the sciatic nerve?

Answer 22

Formed from L4-S3 in the sacral plexus in the pelvis
Exits the pelvis from the greater sciatic foramen, emerging beneath piriformis in the gluteal region
Descends posterior to the hip through the thigh, underneath biceps femoris
Divides into terminal branches - tibial and common fibular nerves at the apex of the popliteal fossa

Question 23

What does the sciatic nerve supply?

Answer 23

Only supplies the hamstrings (except short head of biceps femoris) via the tibial component
Remaining supply through terminal branches

Question 24

What endangers the sciatic nerve?

Answer 24

Posterior dislocation of the hip joint
Intramuscular injections not given in the upper outer quadrant
Now give IM injections in the lateral thigh as variations in branching can occur that the fibular component may be affected by injection to upper outer quadrant

Question 25

What are the terminal branches of the sciatic nerve?

Answer 25

Tibial nerve --> sural nerve, medial+lateral plantar nerves | Common fibular nerve --> superficial + deep fibular nerves, lateral cutanenous aural nerve

Question 26

What is the course of the tibial nerve?

Answer 26

Continues verticle course of sciatic nerve through popliteal fosa, slips beneath fibrous arch of soleus and descends on tibialis posterior, between the superficial & deep muscles Travels posterior to the medial malleolus (underneath flexor retinaculum) and onto the plantar surface of the foot (with deep posterior leg tendons) Branches into the medial and lateral plantar nerves

Question 27

What spinal routes does the tibial nerve arise and what does it supply?

Answer 27

Anterior division L4 - S3 Motor - Muscles of posterior leg (superficial & deep) + muscles of sole of foot Sensory - sural nerve = posterolateral part of leg, lateral foot - med + lat plantar nerves = plantar surface of foot

Question 28

What is the course of the common fibular nerve & what spinal routes does it arise from?

Answer 28

Posterior division L4 - S2 Heads laterally, medial to biceps femurs and superficial to lateral head of gastrocnemius, winding round the neck of the fibula (lateral compartment) to sink into the substance of fibularis longus, where it divides into terminal branches

Question 29

Terminal branches of common fibular nerve?

Answer 29

Superifical fibular + Deep fibular | Lateral cutaneous sural

Question 30

What does the common fibular nerve supply?

Answer 30

Motor from terminal branches | Upper lateral cutaneous sural nerve supplies upper lateral leg and gives communications to the sural nerve

Question 31

What is the course of the DEEP fibular nerve & what does it supply?

Answer 31

Beings in fibularis longus and descends deep to EDL and anterior to IO membrane Passes beneath the extensor retinaculum with tendons of the anterior compartment of the leg and onto the dorsum of the foot Motor - muscles of anterior compartment of the leg (EDL, EHL, Tibialis anterior, fibularis tertius) Sensory - 1st toe cleft, articular branches to ankle and foot

Question 32

What is the course of the SUPERFICIAL fibular nerve and what does it supply?

Answer 32

Descends in the lateral compartment of the leg Motor - muscles of lateral compartment of leg (fibularis longus + brevis) Sensory - lower lateral leg (common fibular does upper lateral part) and dorsum of foot (tibial nerve does plantar)

Question 33

What causes a 'foot drop'?

Answer 33

fracture/laceration to the neck of the fibula can damage the common fibular nerve Affects motor supply to the muscles of the anterior and lateral compartments of leg Anterior muscles - dorsiflex and extend toe + eversion (FT) Lateral muscles - eversion of foot Therefore can't dorsiflex, evert foot or extend toes = foot drop