Nerve Injuries of the Lower Limb Flashcards
How can you classify nerve injuries?
- Neurapraxia - conduction block
- Axonotmesis - Axons divided
- Neurotmesis - Nerve divided
What is neurapraxia?
- Mildest type of nerve injury
- Temporary physiological block of conduction in the axon without loss of axon continuity
- Endoneurium, perineureum and epineurium are intact and no Wallerian degeneration.
- Sensory and motor dysfunction distal to the site of injury as no conduction occurs accross the area of injury.
- Full recovery of the nerve will occur over days - weeks.
What is axonotmesis?
- Loss of continuity of the axons and their myelin sheath
- Endoneurium, perineurium and epineurium are preserved
- Wallerian degeneration commences within 24-36 hours distal to the site of injury
- Axonal regeneration then occurs and recovery is usually possible without surgical intervention.
- Axonal regeneration occurs at 1-3mm/day - time to recovery depends on dostance from site of injury to target organ.
What is neurotmesis?
- Partial or complete division of the axons, endoneurium, perineurium and epineurium of a nerve fibre.
- Wallerian degeneration occurs distal to the site of injury and sensory, motor and autonomic defects are severe.
- Surgical intervention is ALWAYS necessary - even if incomplete division, the deposition of scar tissue between the divided fasicles prevents regeneration.
What is Wallerian degeneration?
- This is when the axon distal to the injury degrades.
- This process usually starts between 24-36 hours of injury.
- Prior to degeneration, the distal axon stumps remain electrcally excitable.
- After injury, the axonal skeleton dsintegrates and the axonal membrane breaks apart.
- Axonal degeneration is followed by degredation of the myelin sheath and infiltration by macrophages (recuited by Schwann cells).
- Macrophages and Schwann cells phagocytose the debris over the subsequent 10-14 days.
- Within 3 days, Schwann cells start to proliferate and by three weeks, they form lines of cells called “bands of bunger” that guide the direction of axon regeneration. Denervated muscle undergoes atrophy.
If axon regeneration is successul, the axon reinnervates the muscle, muscle regeneration starts to occur and function is ultimately restored (althout take several months).
But, if the severed ends are not surgically reapposed, ineffective unregulated regeneration of axons occur. A Traumatic neuroma (sprouting of axons from severed ends of the nerve) forms which can be very painful. Reinnervation of the muscle does not occur and eventally muscle is replaced by fibrous tissue and fat.
What can cause a nerve injury?
- Injury: stretch of nerve, complete division
- Extrinsic pressures: tumour, abscess, ect.
- Medical conditions:
- Diabetes
- Vasculitis
- Alcohol excess
- Drugs
- Other rarer causes: nerve tumours ect.
How does a nerve repair itself?
WALLERIAN DEGENERATION.
Usually, after 3 months the nerve and the muscle around it has regenerated.
If not if can cause a neuroma which is a disorgansied axon sprout.
What are the myotomes of the lower limb?
- L2: Hip flexion
- L3: knee extension
- L4: ankle dorsiflexion
- L5: Great toe extension
- S1: ankle plantar-flexion
- S2: Great toe flexion
What are the dermatomes of the lower limb?
How can you work out where a prolapsed disc is?
Test the ability to perfrom these actions, conduct there reflexes and have sensation in these areas.
Sciatic nerve
- Largest nerve in the body
- Nerve roots L4-S3
- Supplies most of lower limb
- Exits sciatic notch anterior to piriformis, but posterior to short external rotators
- Travels between adductor magnus and long head of biceps femoris.
- Bifurcates into tibial and common peroneal (fibular) nerve in popliteal fossa (but varients!).
What is piriformis syndrome?
- Sciatica symptoms not origionating from spinal roots and/or spinal compression, but involving compression of the sciatic nerve from the overlying periformis muscle.
- Overuse of muscle leads to spasm
- Diagnosis of exclusion
What are the symptoms and treatment of piriformis syndrome?
Symptoms:
- A dull ache in the buttock
- Typical sciatica pain in the thigh, leg and foot
- Pain when walking up stairs or inclines
- Increased pain after prolonged sitting
- Reduced range of motion of the hip joint
Treatment:
- Activity modification,
- NSAIDs
- Physiotherapy (muscle stretching and strengthening exercises)
Lateral cutaneous nerve of the thigh
- The lateral cutaneous nerve of the thigh passes from the lateral border of psoas major across the iliac fossa to pierve the inguinal ligament.
- Travels in a fibrous tunnel medial to the anterior superior iliac spine (ASIS)
- Enters the thigh deep to the fascia lata before becoming superficial 10cm below inguinal ligament
- Supplies the anterolateral aspect of the thigh
What is meralgia paraesthetica?
- Compression of the lateral cutaneous nerve as it passes through the inguinal ligament or as it pierces the fascia lata
- Causes inc. obesity (compression by abdominal fat), pregnancy, tight clothing, wearing a tool belt too tight.
- Burning or stinging sensation in the distribution of the nerve over the anterolateral aspect of the thigh
- Aggrevated by walking or standing
- Relieved by lying down with the hip flexed
- Tenderness on palpitation, reduced sensation; possibly a positive Tinel’s sign.
- Diagnosis confirned by:
- Abscence of motor signs
- Excluding pelvic snf intra-abdominal causes of irritation such as a tumour
- Corsets and tight belts avoided
- Local nerve blocks may be beneficial
- Surgical interventions should be restricted to freeing the nerve; divisions may aggrevate the origional symptoms.
What happens if you damage the femoral triangle?
- Weakness of quadriceps, hip flexors
- Loss of saphenous nerve, intermediate and medial cutaneous nerves of the thigh.
- Flexion compromised
- Active extension of knee and knee jerk reflex lost
- Parasthesia on anteromedial thigh and medial leg - sometimes extending down medial border of the foot.
