MSK Nerves of the lower limb

Question 1

Where is the lumbar plexus located?

Answer 1

In the lumbra region, within the psoas major and anterior to transverse process of lumbar vertebrae

Question 2

What are the spinal nerves forming the lumbar plexus?

Answer 2

T12-L4
At each vertebral level paired spinal nerves leave the spinal chord via the intervertebral foramina. The nerves then divide into anterior and posterior - the lumbar plexus is the anterior fibres

Question 3

List the major peripheral nerves of the lumbar plexus

Answer 3

Iliohypogastric nerve 
Ilioinguinal nerve
Genitofemoral nerve
Lateral cutaneous nerve of the thigh
Obturator nerve
Femoral nerve

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Question 4

What is lumbosacral plexopathy?

Answer 4

Rare disorder affecting either lumbar or sacral plexus

The symptoms cannot be localised to a single nerve - may be numbness, weakness, muscle wastage

Main cause is diabetic amyotrophy - high blood sugar levels damage the nerves
Tumors can cause compression of the plexus

Question 5

Describe the Iliohypogastric nerve

Answer 5

Runs along posterior abdo wall to the iliac crest.

Nerve roots are L1 with some contribution of T12
Motor functions: internal oblique and transversus abdominis
Sensory functions: posterolateral gluteal skin

Question 6

Describe the Ilioinguinal nerve

Answer 6

Roots: L1
Motor functions: (same as iliohypogastric) internal oblique and transversus abdominas

Sensory functions: skin of upper middle thigh and genitalia

Question 7

Describe the Genitofemoral nerve

Answer 7

Roots: L1 L2
Motor functions: genital branch innervates a muscle in the testis
Sensory functions: Genital branch innervates skin of genitals and femoral branch innervates skin of upper anterior thigh

Question 8

Describe the Lateral cutaneous nerve of thigh

Answer 8

Purely sensory function
Enters thigh at lateral inguinal ligament

Roots: L2 and L3

Sensory functions: anterior and lateral thigh down to knee

Question 9

Describe the Obturator nerve

Answer 9

Roots: L2 3 4
Motor functions: medial adductors of thigh (adductor longus brevis magnus, gracilis, pectineus and obturator externus)

Sensory functions: skin of medial thigh

Question 10

Describe the Femoral nerve

Answer 10

Largest branch of lumbar plexus

Roots: L2 3 4
Motor functions: hip flexers (iliacus, pectineus, sartorius) all quads
Sensory functions: anterior thigh (anterior cutaneous branches) and medial leg (saphenous nerve)

Question 11

What is the anatomical course of the femoral nerve?

Answer 11

Descends from lumbar plexus in the abdo through the psoas major muscle
The nerve travels through the pelvis to midpoint of inguinal ligament, goes behind ligament into the thigh and splits into anterior and posterior division

Passes through femoral triangle and gives off articular branches to knee and hip joints.
The terminal branch is the saphenous nerve which passes through adductor canal into leg

Question 12

What are the signs of damage to the saphenous nerve?

Answer 12

Pain paraesthesia or complete loss of sensation of medial side of lower leg

Question 13

What is the anatomical course of the obturator nerve?

Answer 13

Runs through psoas major along the pelvic wall to obturator foramen. Enters the thigh through the obturator canal and splits into anterior and posterior divisions.

Anterior division descends between adductor longus and brevis. It then pierces fascia lata to become the cutaneous branch of obturator nerve.

Posterior division descends through obturator externus then anteriorly to adductor magnus

Question 14

Where is the sacral plexus located?

Answer 14

Posterior pelvic wall, anterior to piriformis

Question 15

What are the spinal nerves that make up the sacral plexus?

Answer 15

S1-4

Receives contributions from L4-5 which combine to form the lumbosacral trunk

Question 16

Name the branches of the sacral plexus

Answer 16

Superior + inferior gluteal nerve 
Sciatic nerve 
Posterior femoral cutaneous nerve 
Pudendal nerve 
Nerve to piriformis, obturator externus and quadrator femoris

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Question 17

What are the 2 main destinations for the nerves of the sacral plexus?

Answer 17

Leave the pelvis via the great sciatic foramen and enter the gluteal region

Remain in the pelvis and innervate structures there

Question 18

Describe the superior gluteal nerve

Answer 18

Accompanied by superior gluteal artery and vein for musch of its course

Roots: L4 5 S1
Motor functions: glut med min, tensor fascia lata
No sensory

Question 19

Describe the inferior gluteal nerve

Answer 19

Accompanied by inferior gluteal artery and vein for much of its course

Roots: L5 S 1 2
Motor functions: glut max
No sensory

Question 20

Describe the posterior femoral cutaneous nerve

Answer 20

Roots: S1 2 3
No motor
Sensory: posterior thigh and leg and perineum

Question 21

Describe the pudendal nerve

Answer 21

Roots: S 2 3 4
Motor functions: perineal muscles, sphincter
Sensory functions: penis and clit

Question 22

What are the roots of the sciatic nerve?

Answer 22

L4 5 S1 2 3

Question 23

What are the 2 terminal branches of the sciatic nerve?

Answer 23

Tibial branch

Common fibular branch

Question 24

Describe the tibial branch of the sciatic nerve

Answer 24

Motor functions: innervates all posterior thigh muscles except short head of biceps femoris, all posterior leg and all foot

Sensory functions: posterolateral and lateral foot and sole

• medial calcaneal branches innervate heel skin
• medial plantar nerve innervates lateral 3 1/2 digits and associated sole area
• lateral plantar nerve innervates lateral 1 2/2 digits and associated palm area

Question 25

Describe the common fibular branch of the sciatic nerve

Answer 25

Motor functions: short head of biceps femoris, all anterior and lateral leg and extensor digitorum brevis

• superficial fibular innervates lateral leg muscles
• deep fibular nerve innervates anterior leg muscles and intrinsic muscles of foot

Sensory functions: anterolateral leg and dorsal of foot

• superficial fibular innervates anterolateral leg and dorsal of foot
• deep fibular nerve innervates skin between 1st and 2nd toes

Question 26

What is the anatomical course of the sciatic nerve?

Answer 26

Enters glut region via the greater sciatic foramen and emerges inferiorly to piriformis

Enters posterior thigh by passing deep to long head of bicep femoris

When it reaches the apex of the popliteal fossa it terminates by bifurcating into the tibial and common fibular nerves

Question 27

What are the motor functions of the sciatic nerve?

Answer 27

Posterior thigh and hamstring part of adductor magnus

Question 28

What is the best site for intramuscular injections in the gluteal region and why?

Answer 28

Split bum into 4 quadrants?:
one line vertically from highest point of iliac crest
the other line passes horizontally midway between highest point of iliac crest and ischial tuberosity

Injection given in upper lateral quadrant to avoid the sciatic nerve

Question 29

What is tarsal tunnel syndrome?

Answer 29

The tibial nerve is compressed in the tarsal tunnel by osteoarthritis pr rheumatoid arthritis or post trauma ankle deformities.

There is paraesthesia of ankle and sole of foot which gets is relieved by rest
Treatment includes anti-inflammatory drugs, footware or surgery to cut the flexor retinaculum to release pressure

Question 30

What is the anatomical course of the tibial nerve?

Answer 30

Arises from sciatic nerve at apex of popliteal fossa
Descends down leg posterior to tibia
Passes through tarsal tunnel, posteriorly and inferiorly to the medial malleolus.
Gives off medial calcaneal branches to innervate heel
Gives off medial and plantar branches to innervate sole of foot

Question 31

What is the anatomical course of the common fibular nerve?

Answer 31

Arises from sciatic nerve at the apex of the popliteal fossa
Follows medial border of biceps femoris and gives rise to 2 cutaneous branches.
To enter lateral leg it wraps around neck of fibula and terminates by dividing into superfical and deep fibular nerves

Question 32

What is the cause and result of entrapment of the superficial fibular nerve?

Answer 32

Usually from ankle sprains and twisting which stretches the nerve or where the nerve exits the deep fascia and is compressed (needs surgery)
Pain and parasthesia in the lower leg and dorsum of foot

Question 33

How is the superficial fibular nerve directly damaged?

Answer 33

Fracture of the fibula or a wound to lateral leg