Nerve Palsies in the Limbs

Question 1

What is a dermatome?

Answer 1

A sensory area of skin supplied by a single spinal nerve

Question 2

Is there overlap between adjacent pre- and post-axial dermatomes?

Answer 2

No - limb buds grow out from the body wall in axial lines

Question 3

Why are lower limb dermatomes distorted?

Answer 3

-Rotation, extension and borrowing of skin from the trunk

Question 4

What is Hilton’s Law?

Answer 4

• “The nerves crossing a joint supply the muscles acting on it and the joint itself”
• “The motor nerve to a muscle tends to give a branch of supply to the joint that the muscle moves and another to the skin over the joint”

Question 5

Which nerves supply the hip joint?

Answer 5

• Obturator
• Femoral
• Lateral femoral cutaneous nerve

Question 6

What is a myotome?

Answer 6

A group of muscles supplied by one segment of the spinal cord

Question 7

Give two common anatomical variations of the brachial plexus

Answer 7

• Pre-fixed plexus (C4-8)

- Post-fixed plexus (C6-T2)

Question 8

Name the common brachial plexus lesions

Answer 8

• Downward traction
• C5 and 6 damage
• Arm “porter’s tips”
• Upward traction (breech delivery)
• T1 damage (intrinsic damage)
• Klumpke’s paralysis (clawed hand)

Question 9

How can the axillary nerve be damaged and which deficits would be seen?

Answer 9

• As a complication of: fractured humeral neck, shoulder dislocation and saturday night palsy (pressure on posterior cord of brachial plexus)
• Deficits: loss of shoulder abduction and sensory loss over regimental badge area

Question 10

What are the roots of the radial nerve and where does it travel?

Answer 10

• C5-T1
• Passes between brachioradialis and brachialis to enter the forearm
• Posterior interosseous branch passes between 2 planes of supinator

Question 11

At which anatomical locations is the radial nerve most at risk?

Answer 11

• Spiral groove of humerus and lateral intermuscular septum

- Posterior interosseus branch at the radial neck

Question 12

How can the radial nerve be damaged and which deficits would be seen?

Answer 12

• Fractures of humeral shaft, Saturday night palsy and exposure of the proximal radius
• Deficits: wrist drop (extensors) and sensory deficit in the dorsal 1st web space

Question 13

What are the roots of the median nerve and where does it enter the forearm?

Answer 13

• C7-T1

- Between the two heads of pronator teres

Question 14

At which anatomical locations is the median nerve most at risk?

Answer 14

Volar aspect of the wrist and the cubital fossa

Question 15

What can cause damage to the median nerve and which deficits would be seen?

Answer 15

• Carpal tunnel syndrome, wrist lacerations, supracondylar fractures and Struther’s ligament
• Deficits: thenar wasting , pointing finger and sensory deficit to the volar aspect of the thumb

Question 16

What are the roots of the ulnar nerve and where does it enter the forearm?

Answer 16

• C7-T1

- Passes between the two heads of flexor carpi ulnaris

Question 17

Where is the ulnar nerve most at risk?

Answer 17

-Behind the medial epicondyle of the humerus, wrist and canal of Guyon

Question 18

What can cause ulnar nerve damage and which deficits would be seen?

Answer 18

• Fractures of humeral condyles and wrist lacerations

- Deficits: claw hand, hypothenar and 1st dorsal interosseous wasting and sensory deficit to the little finger

Question 19

Where does the lumbar plexus lie?

Answer 19

On the surface of quadratus lumborum and within the body of the psoas muscle

Question 20

Which major nerves, that lie around the hip, do not exit the pelvis by the sciatic foramen?

Answer 20

• Genitofemoral
• Ilioinguinal
• Femoral
• Lateral femoral cutaneous
• Obturator

Question 21

What are the roots of the femoral nerve and which plexus is it a part of?

Answer 21

• L2-4

- Lumbar plexus

Question 22

Describe the route the femoral nerve takes

Answer 22

• Passes through the Psoas major muscle
• Exits pelvis under the inguinal ligament
• Lateral to femoral artery, vein and lymphatic channels in the femoral triangle

Question 23

Which structures are supplied by the femoral nerve and where do its terminal branches lie?

Answer 23

• Quadriceps muscles in the anterior thigh

- Long fine sensory branch: saphenous nerve

Question 24

What are the roots of the lateral femoral cutaneous nerve and where does it lie?

Answer 24

• L2-3
• On the surface of the iliacus muscle
• Usually exits pelvis under the lateral end of the inguinal ligament

Question 25

What does the lateral cutaneous nerve carry?

Answer 25

Sensation to the lateral aspect of the thigh

Question 26

What happens if the lateral femoral cutaneous nerve is compressed?

Answer 26

Meralgia paraesthetica

Question 27

What are the roots of the sciatic nerve and which plexus is it a part of?

Answer 27

• L4-S3

- Sacral plexus

Question 28

Where does the sciatic nerve run?

Answer 28

• Exits pelvis through sciatic foramen below piriformis muscle
• Runs deep to the gluteus maximus muscle

Question 29

Which structures are supplied by the sciatic nerve?

Answer 29

• Hamstring muscles (posterior thigh)
• Adductor magnus
• All lower leg and foot muscles via terminal branches (tibial and common fibular nerves)

Question 30

What can cause damage to the sciatic nerve?

Answer 30

• Posterior dislocation of the hip
• IM injections
• Surgery

Question 31

What are the roots of the common fibular nerve and which nerve is it a branch of?

Answer 31

• L4-S2

- Sciatic nerve

Question 32

Where is the common fibular nerve at risk and what deficits would be seen?

Answer 32

• As it passes around the lateral aspect of the neck of the fibula
• Deficits: foot drop and slapping gait

Question 33

Which branches does the common fibular nerve give off?

Answer 33

• Superficial and deep fibular nerves

- Communicating branch to the sural nerve