Session 10-Nerve Injuries In The Lower Limb

Question 1

What are the three grades of nerve injury in the Seddon classification system?

Answer 1

1) neurapraxia = conduction block
2) axonotmesis = axon divided
3) neurotmesis = nerve divided

Question 2

What is Wallerian degeneration?

Answer 2

Occurs when nerve fibre is cut or crushed and part of axon distal to injury degenerates

Question 3

What are the causes of neuropathy?

Answer 3

• injury: stretch of nerve, complete division
• extrinsic pressure: tumour, abscess etc
• medical conditions: diabetes, alcohol excess, drugs
• nerve tumours

Question 4

Name the myotomes of the lower limb and the actions they are responsible for

Answer 4

L2: hip flexion
L3: knee extension, hip adduction
L4: ankle dorsiflexion
L5: great toe extension, hip abduction, ankle inversion
S1: ankle plantarflexion, hip extension, ankle eversion
S2: knee flexion, great toe flexion

Question 5

What is the motor effect of an L4 prolapsed intervertebral disc?

Answer 5

Effects tibialis anterior - weak ankle dorsiflexion

Question 6

What is the motor effect of an L5 prolapsed intervertebral disc?

Answer 6

Extensor hallucis longus -> weak great toe extension

Question 7

What is the motor effect of an S1 prolapsed intervertebral disc?

Answer 7

Loss of ankle plantarflexion (affects gastrocnemius and soleus)

Question 8

Which is the largest nerve in the body?

Answer 8

Sciatic nerve

Question 9

In between which two muscles does the sciatic nerve travel?

Answer 9

Adductor Magnus and long head of biceps femoris

Question 10

What does the sciatic nerve bifurcate into and where does this occur?

Answer 10

Tibial and common fibular nerve in popliteal fossa

Question 11

What is piriformis syndrome?

Answer 11

Sciatica symptoms not originating from spinal roots and/or spinal disc compression but involving overlying piriformis muscle

Question 12

What does the overuse of the piriformis muscle lead to?

Answer 12

Spasm

Question 13

Describe the anatomical course of the lateral cutaneous nerve of the thigh

Answer 13

Passes from lateral border of psoas major across iliac fossa to pierce inguinal ligament
Travels through fibrous tunnel medial to ASIS and enters thigh deep to fascia lata before continuing distal into subcutaneous tissues
Divides into anterior and posterior branches distal to inguinal ligament

Question 14

Where does the lateral cutaneous nerve of the thigh innervate?

Answer 14

Anterolateral aspect of the thigh

Question 15

What is meralgia paraesthetica?

Answer 15

Compression of lateral cutaneous nerve of the thigh as it passes through inguinal ligament or pierces fascia lata

Question 16

What are the causes of meralgia paraesthetica?

Answer 16

Obesity
Pregnancy
Tight clothing
Wearing a tool belt

Question 17

Describe how meralgia paraesthetica presents and what: a) aggravates and b) relieves the symptoms

Answer 17

Burning or stinging sensation in distribution of nerve over anterolateral aspect of thigh, tenderness on palpation and reduced sensation

a) walking or standing
b) lying down with hip flexed

Question 18

How is diagnosis of meralgia paraesthetica confirmed?

Answer 18

Absence of motor signs and exclusion of pelvic and intra-abdominal causes of irritation such as tumour

Question 19

What is beneficial when treating meralgia paraesthetica?

Answer 19

Nerve blocks

Question 20

Which muscles are paralysed in a femoral nerve injury and which associated movements are affected?

Answer 20

• iliacus = hip flexion
• sartorius = hip flexion and abduction
• pectineus = hip flexion and adduction
• quadriceps femoris = knee extension

Question 21

Describe the anatomical course of the tibial nerve

Answer 21

• Crosses popliteal fossa
• Deep to soleus
• In posterior compartment between flexor digitorum longus and flexor hallucis longus
• Passes deep to flexor retinaculum
• Gives off medial calcaneal nerve
• divides into medial and lateral plantar nerves

Question 22

Which muscles does a tibial nerve injury affect and which associated movements are affected?

Answer 22

Loss of posterior leg compartments - gastrocnemius, tibilais anterior and long flexors

Weakness of plantarflexion and inversion

Question 23

What is calcaneovalgus posture?

Answer 23

Unopposed pull of dorsiflexors and everters in tibial nerve injury leading to dorsiflexed and everted foot

Question 24

Where is sensation lost in a tibial nerve injury?

Answer 24

Plantar sensation except medial and lateral sides supplied by saphenous and sural nerves

Question 25

Which movements are lost in a common fibular nerve injury?

Answer 25

Loss of ankle everters and dorsiflexors

Question 26

Where is sensation lost in a common fibular nerve injury?

Answer 26

Loss of sensation in lateral calf and dorsal aspect of foot

Question 27

Which muscles and associated movements are affected in a superficial fibular nerve injury?

Answer 27

Fibularis longus and brevis

Weakness in eversion

Question 28

Where is sensation lost in a superficial fibula nerve injury?

Answer 28

Most of skin of dorsum of foot and anterolateral calf

Question 29

What are the causes of injury to superficial fibular nerve?

Answer 29

Ankle surgery via lateral approach

Ankle arthroscopy portal placement

Question 30

Which muscles and associated movements are affected in a deep fibular nerve injury and what does this lead to?

Answer 30

Anterior muscles: tibilais anterior, extensor hallucis longus, extensor digitorum longus, fibularis tertius

Weakness in ankle dorsiflexion -> foot drop

Question 31

Where is sensation lost in a deep fibular nerve injury?

Answer 31

1st web space

Question 32

How does saphenous nerve injury occur and what does this lead to?

Answer 32

Stripping of long saphenous vein varicosities

Nerve accompanies vein -> loss of sensation over medial leg

Question 33

What causes sural nerve injury and what does this lead to?

Answer 33

Surgical injury during posterior approach to ankle, Achilles’ tendon, short saphenous vein

Loss of sensation to sole of foot