L12: Nerve injuries in the lower limb

Question 1

Describe the basic structure of a neurone?

Answer 1

Dendrites--> thin structures arising from the cell body 
Cell body--> Collates information 
Axon hillock--> origin of axon
Axon--> specialised cellular extension
Synaptic knob--> synapses

Question 2

Describe the basic structure of a nerve?

Answer 2

Bundle of axons and supporting cells
Axon surrounded by endoneurium (glucocalyx and mesh of collagen)
Bundle of axons–> fascicles
Fascicle surrounded by perineurium
Fascicles grouped and surrounded by epineurium
Own blood supply–> vasa nervorum

Question 3

What is the endoneurium?

Answer 3

Glycocalyx and mesh of collagen
Surrounded by endoneurial fluid
Similar to blood brain barrier and CSF

Question 4

What is the Seddon classification?

Answer 4

Way of classifying nerve injuries

Question 5

What are the different classes in the Seddon classification?

Answer 5

Class I: Neurapraxia
Class II: Axonotmesis
Class III: Neurotmesis

Question 6

What is Neurapraxia?

Answer 6

Mildest type 
Temporary physiological block of conduction of the affected neuron- No conduction across damaged area- Proximal and distal normal
Endo-, Peri- and epineurium all in tact 
No Wallerian degeneration 
Sensory and motor loss distal to injury 
Full recovery--> Period of days to weeks

Question 7

What is Axonotmesis?

Answer 7

Loss of continuity of axon and myelin sheath
Endo-, Peri and epineurium are preserved
Wallerian degeneration–> 24-36 hours –> distally
Axonal regeneration–> full recovery without surgery
Axon regeneration proceeds at 1-3mm/day–> time of recovery depends on distance from site of injury

Question 8

What is Neurotmesis?

Answer 8

Partial or complete division of axons, endo-, peri- and epineurium
Wallerian degeneration –> sensory, motor and autonomic defects severe
Surgical intervention always required
Deposition of scar tissue prevents regeneration

Question 9

What is Wallerian degeneration?

Answer 9

Axon distal to injury degenerates–> antegrade or orthograde degeneration (away from cells body)
Starts within 24-36 hours
Prior to degeneration–> distal axon stump is electrically excitable

Question 10

Describe the process of Wallerian degeneration?

Answer 10

1. After injury–> axon skeleton disintegrates, and axonal membrane breaks apart
2. Followed by degeneration of myelin sheath and infiltration by macrophages
3. Macrophages and Schwann cells phagocytose debris–> 10-14 days
4. Within 3 days Schwann cells begin regeneration–> 3 weeks formed ‘Bands of Bunger’–> guide axon regeneration –> denervated muscle atrophys
5. Axon regeneration successful–> muscle innervated-> muscle regeneration

Question 11

What happens if regeneration is unsuccessful?

Answer 11

If ends not surgically reopposed, ineffective, unregulated regeneration of axons occurs
Sprouting of axon–> traumatic neuroma forms
Painful
Reinnervation does not occur–> muscle replaced by fibrous tissue and fat

Question 12

What are some of the other causes of neuropathy?

Answer 12

Traction (stretch)
Extrinsic pressure–> tumour, abscess, displaced fracture
Medical conditions–> diabetes, alcohol excess and drugs
Tumours of nerves–> Neurofibromas, acoustic neuroma (vestibulocochlear nerve)

Question 13

What is a prolapsed intervertebral disc?

Answer 13

Commonly called a slipped disc

IVD pushes out of place

Question 14

What are the most common sites for nerve root injuries caused by a prolapsed IVD? Why?

Answer 14

L4/5 and L5/S1

Due to mechanical loading at these joints

Question 15

In the lumbar and sacral region of the spine how do the nerve roots exit?

Answer 15

Emerge below the respective vertebrae–> L4 exits in L4/5 Intervertebral foramen

Question 16

What is the nerve root that exits at the level called? What is the nerve root that exits below called?

Answer 16

Exiting nerve root–> exits at same level

Traversing nerve root–> emerges at level below

Question 17

In the lumbar spine which nerve root is normally damaged by a paracentral herniation?

Answer 17

Traversing nerve root

Question 18

What is the root value of the sciatic nerve? Which muscles does it innervate?

Answer 18

L4, L5, S1, S2, S3
Hamsting muscles–> Biceps femoris, Semimembranosus, Semitendinosus
Adductor magnus (hamstring portion)
Still single sciatic nerve but common peroneal component innervates the short head of biceps femoris, other hamstring innervated by tibial
portion
Branches at popliteal fossa–> Tibial (posterior compartment) and Common peroneal (superficial- lateral, deep- anterior)
Also innervates muscles of the leg and foot

Question 19

What is the cutaneous supply of the sciatic nerve?

Answer 19

Innervates skin of
Common peroneal - proximal lateral leg (anterior)
-Superficial peroneal (fibular) nerve- Distal lateral leg and dorsum of foot
- Deep peroneal (fibular) nerve- Between great toe and next toe!

Tibial nerve - Heel of foot (posterior)
–> Medial plantar–> medial sole of foot up to medial 3.5 toes
–> Lateral plantar–> Lateral sole of foot and lateral 1.5 toes
Sural nerve- posterior distal lateral leg (ankle) and lateral side of foot and little toe
(posterior)

Question 20

What is the normal course of the sciatic nerve from the pelvis to the leg?

Answer 20

1. Exits via the greater sciatic foramen (going posteriorly)
2. Anterior and inferior to piriformis
3. Posterior surface of short external rotators (superior gemellus, obturator internus, inferior gemellus and quadratus femoris)
4. Enters posterior thigh–> deep to long had of biceps femoris (between biceps femoris and adductor magnus)
5. Bifucates into tibial and common peroneal at apex of popliteal fossa

Question 21

What are some of the different anatomical variants of the sciatic nerve?

Answer 21

Entry into the gluteal region:

• 90% inferior to piriformis (normal)
• Sciatic nerve split–> piriformis split–> one exits between muscles and one below
• Sciatic nerve split–> piriformis normal–> one exits above one below
• Piriformis split–> exits between muscle

Question 22

What is piriformis syndrome?

Answer 22

Sciatic nerve symtoms NOT due to compression of nerve roots BUT compression of sciatic nerve by piriformis muscle

Question 23

What are the symptoms of piriformis syndrome?

Answer 23

Dull ache in buttock 
Sciatic pain in thigh, leg, foot
Pain when walking up stairs or inclines 
Increased pain after prolonged sitting 
Reduced range of motion of the hip joint

Question 24

What are the causes of piriformis syndrome?

Answer 24

Spasms of piriformis muscle –> overuse
Direct trauma
Anatomical variation between nerve and muscle (least common)

Question 25

How is piriformis syndrome treated?

Answer 25

Activity modification NSAID Physiotherapy

Question 26

What would happen if the sciatic nerve was completely transected in the buttock?

Answer 26

Hip movement normal--> Gluteus maximus (inferior gluteal nerve), flexion unaffected (flexors--> femoral nerve), adduction unaffected (obturator nerve), abduction unaffected (gluteus medius and minimus--> superior gluteal nerve) Hamstring paralysed Knee extension unaffected--> Quadriceps femoris--> femoral nerve Knee flexion absent--> Flexors --> sciatic nerve (except gracilis (obturator nerve) and sartorius (femoral) but not strong enough) Dorsiflexion and plantar flexion, inversion and eversion--> paralysed All movements of toes--> paralysed Paraesthesia in lateral leg and foot (common fibular nerve) Paraesthesia in posterior leg and plantar surface of foot (tibial nerve)

Question 27

What is the nerve root of the superior gluteal nerve? WHat does it innervate?

Answer 27

L4, L5 and S1 | Innervates Gluteus medius and minimus and tensor fascia latae

Question 28

What is the anatomical course of the Superior gluteal nerve?

Answer 28

Exits through the greater sciatic foramen above piriformis (with artery and vein)

Question 29

What happens during superior gluteal nerve injury?

Answer 29

Normally gluteus medius and minimis contract when opposite foot off the ground raising the pelvis on the opposite side--> allowing leg to be brought through without hitting the ground in walking Injury--> no contraction of gluteus medius and minimis hence the pelivis on the opposite side drops--> Positive Trendelenburg sign--> foot will catch ground when walking --> patient has to use trunk muscles to raise the pelvis --> Trendelenburg gait

Question 30

What is Meralgia paraesthetica?

Answer 30

Injury to lateral cutaneous nerve of the thigh (branch of lumbar plexus, dorsal division L2-3) Compression of the nerve as it pierces the inguinal ligament or fascia latae in the thigh Patient experiences burning/stinging sensation over the anterolateral aspect of the thigh Tenderness on palpation Reduced sensation in distribution of the nerve Positive Tinel's sign--> percussing the nerve at the site of entrapment generate tingling or paraesthesia in distribution of nerves

Question 31

What causes Meralgia paraesthetica? What aggrevates it? How is it relieved?

Answer 31

Obesity (abdominal fat compression), pregnancy, tight clothing, wearing a tool belt Aggrevated by standing or walking Relieved by lying down with hip flexion

Question 32

What is the course of the lateral cutaneous nerve?

Answer 32

1. Emerges from the lateral border of the psoas major on posterior abdominal wall 2. Travels across iliac fossa on surface of iliacus muscle 3. Pierce lateral inguinal ligament 4. Travels in fibrous tunnel medial to ASIS of pelvis and enters the thigh deep to the fascia lata 5. Divides into anterior and posterior branches 6. Becomes superficial 10cm below inguinal ligament and supplies the anteriolateral aspect of thigh

Question 33

How is Meralgia paraesthetic diagnosis confirmed? How is it treated?

Answer 33

Absence of motor signs Excluding intra-abdominal causes of nerve irritation such as tumour Avoid corsets and tight belts Local nerve block and sometimes surgery to release trapped nerve necessary

Question 34

What is the spinal root of the femoral nerve? What is the course of the femoral nerve?

Answer 34

L2, 3 and 4 in lumbar plexus Enters femoral triangle beneath inguinal ligament Lateral to Femoral artery (NAVEL) Divides into multiple branches 4cm below the inguinal ligament

Question 35

What is the motor innervation of the femoral nerve? What is the sensory distribution?

Answer 35

Anterior thigh muscles --> Flex hip (pectineus, iliacus, sartorius) --> Extend the knee (Quadriceps femorsis) Sensory--> anteromedial thigh and medial side of leg and foot --> Via anterior femoral cutaneous nerve or medial and intermediate cutaneous nerves of the thig), and via saphenous nerve respectively

Question 36

What causes injury to the femoral nerve?

Answer 36

Fracture of pelvis or hip Penetrating wounds Rare--> surgery (hip replacement or abdominopelvic operations)

Question 37

What is the clinical presentation of femoral nerve injury?

Answer 37

Depends on site of injury Weakness and wasting of quadriceps femoris Hip flexion compromised--> Although Psoas major and minor, adductor brevis, adductor longus, gracilis and tensor fascia latae nerve supply still intact and they flex the hip Extension of knee and knee jerk reflex lost--> Quads absent Anaesthesia/ paraesthesia on anteromedial thigh and medial leg--> medial border of foot

Question 38

What is the spinal root of the tibial nerve? What is it a branch of? What is its course?

Answer 38

L4-S3 Branch of sciatic nerve Crosses popliteal fossa Deep to soleus muscle Between flexor digitorum longus and flexor hallucis longus muscle Passes beneath flexor retinaculum at the medial malleous--> medial calcaneal branch to the heel Divides into medial and lateral plantar nerves to supply the sole of the foot

Question 39

What happens if the tibial nerve is damaged?

Answer 39

Supplies muscles to the posterior leg Paralysis of gastrocnemius and soleus --> no plantarflexion Active flexion of the toes will be lost Inversion of midfoot compromised--> Tibialis posterior paralysed Unopposed pull of dorsiflexors and everts--> foot adopts calcaneovalgus posture (heel down, foot deviated laterally) Loss of sensation on sole of foot except middle part of medial side of foot (saphenous nerve) and posterior lateral part of heel (sural nerve)

Question 40

What is the spinal root value of the common peroneal nerve? What is it a branch of? What is its anatomical course?

Answer 40

L4-S2 Branch of Sciatic nerve Travels along superolateral border of popliteal fossa on medial border of biceps femoris Winds around neck of fibula Pierce the peroneus longus muscle Gives off cutaneous branch which supplies skin of lateral leg Divides into superficial and deep peroneal nerve

Question 41

What causes injury to the common peroneal nerve?

Answer 41

``` Prolonged bed rest Pressure from tight plaster cast Poorly places stirrups during surgery Fracture to neck of fibula --> injury to common peroneal nerve where it winds around neack of fibula ```

Question 42

What is the clinical presentation of fibular nerve injury?

Answer 42

Foot drop--> paralysis of tibialis anterior and long extensors of toes Inversion of ankle--> paralysis of peroneus (fibularis) longus and brevis Loss of sensation on lateral leg and dorsal aspect of their foot

Question 43

What is the root value of the superficial peroneal (fibular) nerve? What is it a branch off? What is is anatomical course?

Answer 43

L4-S1 Common peroneal nerve Lateral compartment innervator Commences at neck of fibula, descends between peroneus longus and brevis and lateral aspect of extensor digitorum longus --> supplies peroneus longus and brevis Continues as cutaneous--> anterolateral leg Reaches distal 1/3 of leg, pierces deep fascia to run subcutaneously and supplies the dorsum of the foot, excluding the first webspace (deep peroneal nerve), medial border (saphenous nerve) and lateral border (sural nerve)

Question 44

What can cause injury to the superficial peroneal nerve? What is the clinical presentation?

Answer 44

Fracture to proximal fibula or penetrating injury to lateral leg--> loss of eversion, loss of sensation over distal anterolateral leg and dorsum of foot, excluding first webspace Ankle arthroscopy or ankle surgery (lateral approach)--> sensory loss to dorsum of foot only

Question 45

What is the root value of the deep peroneal nerve? What is it a branch off? What is its anatomical course?

Answer 45

L4, 5 Common peroneal nerve Anterior compartment innervator Commences at neck of fibula Pierce intermuscular septum to enter anterior compartment Pierces extensor digitorum longus, next to anterior tibial artery, follows artery, between tibialis anterior and EDL in proximal leg and then between TA and EHL in distal leg, at ankle divides into medial and lateral branches

Question 46

What does the deep peroneal nerve supply in the leg?

Answer 46

``` Tibialis anterior Extensor hallucis longus Extensor digitorum longus Peroneus tertius Small patch of skin over first dorsal webspace ```

Question 47

What causes deep peroneal nerve injury? What is the clinical presentation?

Answer 47

Common site of mononeuropathy (single nerve dysfunction of lower limb) caused by motor neurone disease, diabetes, ischaemia and vasculitis Total knee replacement can cause injury Clinical--> Foot drop, inability to extend toes, small patch of numbness in first dorsal webspace

Question 48

What is the root value of the saphenous nerve? What type of nerve is it? (motor/ sensory)

Answer 48

L3 and L4 Sensory nerve Branch of femoral nerve

Question 49

What is the anatomical course of the saphenous nerve?

Answer 49

Branches from femoral nerve in femoral triangle Anterior to femoral artery in the subsartorial canal as far as hiatus in adductor magnus Continues to descend vertically along medial side of knee behind sartorius Pierces fascia lata and becomes subcutaneous Passes along medial side of leg (great (long) saphenous vein), supplying medial leg and medial border of foot as far as 1st metotarsophalangeal joint

Question 50

How is the saphenous nerve damaged?

Answer 50

Saphenous vein cut-down--> obtain venous access in emergency Orthopedic surgery to distal tibial or medial malleolus Damages when obtaining saphenous vein for bypass surgery Port placement for knee athroscopy Past--> damages during stripping of varicose veins--> no commonly done now (thermal or chemically done)

Question 51

What is the sural nerve? What is its anatomical course?

Answer 51

Sensory nerve Communicating branch from tibial nerve and common peroneal nerve that unite in the posterior leg Posterolateral direction, posterior to lateral malleolus and along the lateral aspect of the foot Supplies skin of lateral ankle and foot

Question 52

How is the sural nerve damaged?

Answer 52

Harvested for nerve grafting and reconstructive surgery Relatively minor sensory deficit Past--> damages during stripping of varicose veins (not commonly done)