22 - Nerve Injuries in Lower Limb Flashcards
How do you classify nerve injuries?
Seddon Classification
Class I Neurapraxia: Mild nerve injury with temporary physical blood of conduction in affected axons but no loss of axon continuity. No wallerian degeneration. Sensory and motor dysfunction distant to site of injury and full recovery in days or weeks. Demyelination
Class II Axonotmesis: Loss of continuity of axons and myelin sheath but endo, peri and epineurium in contact. Wallerian degeneration within 24-36 hours distal to injury. Regeneration at 1-3mm a day so recovery depends on distance of site of injury
Class III Neurotmesis: Partial or complete division of axons, eno, peri and epineurium of nerve fibre. Wallerian degeneration distal to injury. Surgical intervention always required as deposition of scar tissue between divided fasicles prevents regeneration
What is Wallerian Degeneration and regeneration of a nerve following an injury?
- Antegrade degeneration of axon distal to injury within 24-36 hours. Before this axon is still excitable
- Axon degeneration followed by degradation of myelin sheath and infiltration by macrophages recruited by Schwann cells
- Macrophages and Schwann cells phagocytose debris over 10-14 days
- In three days Schwann cells proliferate and at 3 weeks form bands of burgers to guide regeneration. In this time denervated muscle undergoing atrophy
- If axons reinnervate muscle, muscle regeneration starts and function restored in few months
What happens in unsuccessful nerve regeneration?
- If severed ends not surgically reappose unregulated regeneration occurs
- Traumatic neuroma from axons sprouting from severed ends
- Painful and reinnervation does not occur so muscle replaced by fibrous tissue and fat
What are some causes of neuropathy?
- Trauma
- Traction (stretch) e.g upper brachial plexus injury during birth
- Extrinsic pressure e.g tumour, displaced fracture
- Medical conditions e.g diabetes, alcohol excess, drugs
- Tumours of nerves e.g neurofibromas
Draw the cutaenous territories of the peripheral nerves on this diagram.
What myotome and dermatome loss would a patient have with paracentral herniation of the following discs:
L3/L4
L4/L5
L5/S1
Would compress traversing nerve root
- L4: weakness of ankle dorsiflexion
- L5: Weakness of great toe dorsiflexion
- S1: Weakness of ankle plantarflexion (inability to stand on tiptoe and ankle reflex lost)
What are the most common sites for a disc herniation?
L4/L5
L5/S1
Due to mechanical loading at these sites
What does the sciatic nerve become as it travels down the leg and what cutaneous branches does it have?
- Splits in tibial and common peroneal
- Tibial splits into sural nerve in lower leg and then medial and lateral plantar nerve and medial calcaneal nerve in sole of foot
- Common peroneal splits into sural communicating branch, lateral cutaneous nerve of calf and deep and superficial peroneal nerve in lower leg
Draw what nerves have what cutaneous distribution on this diagram.
Draw the nerve paths of the tibial and common peroneal nerve.
What is the anatomical course of the sciatic nerve?
- Leaves pelvis and enters gluteal region via greater sciactic foramen, inferior to piriformis
- Passes posterior surface of short external rotators then enters posterior thigh by passing deep to long head of biceps femoris between biceps femoris and adductor magnus
- Birfurcates in apex of popliteal fossa
What are some anatomical variants of the sciatic nerve?
90% of peoples passes inferior to piriformis but other variants
What is piriformis syndrome?
- Compression of sciatic nerve by piriformis causing sciatic like symptoms but no compression of actual nerve roots
- Usually due to spasm of piriformis from overuse, trauma or anatomical variants
- Treatment: activity modification, NSAIDs, physio
If the sciatic nerve was completely transected due to a stab wound in the buttock, what effect would this have on the lower limb?
- Normal hip movement as although hamstrings paralysed, still have gluts supplied by inferior gluteal nerve working
- Adduction unaffected as adductors supplied by obturator
- Knee extension fine as quads supplied by femoral
- Knee flexion, dorsiflexion, plantar flexion, inversion/eversion of foot and movement of toes all absent
What happens when there is an injury to the superior gluteal nerve?
- Supplies glut med and min and tensor fascia lata. Nerve from L4-S1 dorsal divsions in sacral plexus
- Leaves pelvis by greater sciatic notch above piriformis
- Trendelenburgs Sign
What is Meralgia Paraesthetica?
- Injury to lateral cutaneous nerve of the thigh which is a direct branch of lumbar plexus from dorsal divisions L2-L3
- Compression of nerve as it pierces inguinal ligament or fascia lata
- Causes: obesity, pregnancy, tight clothing, tool belt
- Symptoms: burning stinging sensation on anterolateral thigh, symptoms aggravated by walking or standing and relieved by lying down with hip flexed, reduces sensation in nerve distribution, positive Tinel’s sign
What is Tinel sign?
Way to detect irritated nerves. It is performed by lightly tapping (percussing) over the nerve to elicit a sensation of tingling or “pins and needles” in the distribution of the nerve
How do you confirm meralgia paresthetica and how is it treated?
- Absence of motor signs as purely sensory
- Exclude intraabdominal causes like tumour
- Treat: avoid tight belts and corsets, local nerve block or surgery to relieve trapped nerve
What is the course of the lateral cutaneous nerve of the thigh?
- Emerges from posterior lateral border of psoas and travels across iliac fossa on surface of illiacus
- Pierces lateral aspect of inguinal ligament
- Travels in fibrous tunnel medial to ASIS and enters thigh deep to fasica lata where it divides into anterior and posterior branches
- Becomes superficial 10cm below inguinal ligament to supply anterolateral thigh
What is the course of the femoral nerve and what is it’s cutaneous distribution?
- L2 to L4 lumbar plexus and enters femoral traingle beneath inguinal ligament lateral to femoral artery
- 4cm below ligament divides into multiple branches: saphenous, intermediate cutaneous nerve of thigh and medial cutaneous nerve of thigh (anterior cutaneous branches)
Draw a nerve path of the femoral nerve.
What are some causes of femoral nerve injury and what are some of the signs?
- Uncommon but penetrating wounds near groun, hip/pelvis fractures, surgery like a hip replacement or operations where retractors are used
- Weakness and wasting of quads so hip flexion is compromised but not lost as gracillis, adductor brevis, adductor longus, psoas major and minor, tensor fascia lata all still flex with different nerve supply
- Knee extension lost and knee jerk absent
- Paraesthesia on anteromedial thigh and medial leg
What is the anatomical course of the tibial nerve?
- Larger branch of sciatic nerve L4-S3
- Cross popliteal fossa and passes deep to soleus into deep posterior leg between FDL and FHL
- At ankle passes beneath flexor retinaculum at medial malleolus and gives of medial calcaneal branch to heel and medial and lateral plantar nerves to sole of foot.
How is the tibial nerve injured and how does it present?
- Proximal popliteal fossa injury but this is uncommon
- Cannot plantarflex ankle as lost gastro and soleu so canntoot stand on tiptoe
- Cannot flex toes
- Inversion of foot compromised but not lost as tibialis anterior (deep peroneal) intact not tibialis posterior though
What are the causes of common peroneal nerve injury and how does it present?
Causes: mainly around neck of fibula as winds around here so prolonged bed rest, tight plaster cast, poorly place stirrups in gynae or anal surgery, fractures of fibula neck
Symptoms:
- Foot drop as paralysis of tibialis anterior and long toe extensors
- Inversion of ankle due to paralysis of fibularis brevis and longus that evert ankle
- Loss of sensation of lateral leg and dorsal foot
What is the anatomical course of the common peroneal nerve?
- L4-S2 and smaller branch of sciatic
- Superior popliteal fossa and travels along superolateral border of fossa on medial border of biceps femoris
- Winds around neck of fibula to pierce fibularis longus and divide into superficial and deep peroneal nerves
- Before it divides it gives of cutaneous branch to supply skin of upper lateral leg
What is the anatomical course of the superficial peroneal nerve?
- Branches from common peroneal at neck of fibula and descends between peroneus longus and brevis and lateral EDL
- Supplies peroneus longus and brevis and then continues purely sensory
How can the superficial peroneal nerve be injured and how does it present?
Cause: fracture of proximal fibula or penetrating injuries to lateral leg.
Symptoms: loss of eversion and loss of sensation to distal anterolateral leg and dorsum of foot, excluding first web space
(can be damaged by ankle arthroscopy but in this only sensory loss occurs)
What is the anatomical course of the deep peroneal nerve?
- At neck of fibula it commences and pierces intermuscular septum. Then pierces EDL and lies next to anterior tibial artery following it’s course before splitting into medial and lateral branches at the artery
Supplies: TA, EHL, EDL, peroneus tertius and first webspace dorsal
What is the presentation of a deep peroneal nerve injury and what is it caused by?
Signs: foot drop, cannot extend toes, numbness in first dorsal space
Causes: knee replacement, motor neuron disease, diabetes, ischameia, vasculitis
What nerve is the most common site of mononeuropathy?
Deep peroneal
What is the anatomical course of the saphenous nerve?
- Cutaneous branch of femoral nerve L3-L4
- Branches from femoral in femoral triangle and travels anterior to femoral artery in subsartorial canal to hiatus in adductor magnus
- Doesn’t pass through hiatus but descends medial side of knee behind sartorius and pierces the fascia lata
- Passes along medial side of leg accompanies by great saphenous vein
What causes a saphenous nerve injury and what is the presentation of this?
Causes:
- saphenous vein cut down (emergency IV in shock)
- distal tibia or medial malleolus surgery
- saphenous vein harvest for CABG
- port placement in knee arthroscopy
- stripping varicose veins (not done often now)
LOSS OF SENSORY DISTAL TO INJURY
Why are there not as many saphenous nerve injuries anymore?
Varicose veins are no longer stripped, there is chemical or thermal intravascular ablation
What is the anatomical course of the sural nerve?
- Made from communicating branches of tibial and common peroneal that unite in posterior leg
- Run posterolaterally to lateral malleolus and along lateral aspect of foot
What happens in sural nerve injury?
- Minor sensory deficit in skin of lateral ankle and foot, usually due to stripping of short saphenous vein
- Used to be harvested for nerve grafting in reconstructive surgery
Quickly summarise what movements are lost in the lower limb if each nerve in the lower limb is injured?
What nerves innervate each compartment of the thigh and what are their nerve roots
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REMEMBER ROTATION OF LIMBS DURING EMBRYO
What is the best way to remember the nerve roots of the brachial plexus?
What is the best way to identify the nerves of the brachial plexus in the DR?
What are the most likely mechanism of injury for each of the nerves of the brachial plexus?
