18. Lower limb nerve injuries Flashcards
Cauda equina vs conus lesions
Conus medullaris - upper motor neuron L1/2 mix Cauda equina - lower motor neuron
Landmarks for lumbar puncture
Cauda equina vs conus medullaris
Cauda equina causes
Disc herniation, spinal fracture, tumour
Conus medullaris infections
Disc herniation, tumour
Inflammatory conditions
- chronic inflammatory demyelinating polyradiculopathy
- Sarcoidosis
Infection
- CMV, HSV, EBV, Lyme, TB
L5/S1 disc herniation effect
Compression of cauda equina
Deformity of thecal sac impinging on the cauda equina
Nerve root entrapment - sciatica
Compression:
- Disc -posterior central
- Lateral Bone- osteophyte
- Ligaments
- Small canal- stenosis
Sciatica – usually L5, S1 n. root impingement
- L5 n. root – exits between L5/ S1 vertebral bodies
- S1 n. root exits between S1 / S2 vertebral bodies
Pain may be felt in dermatome (sharp/ superficial) or myotome (deep ache)
Lower limb root lesions - reflex and sensory loss (dermatomes)
Lower limb root lesions - weakness
Lumbar plexus
Sacral plexus
Lumbrosacral plexus regions
Childbirth (large head, prolonged labour)- esp obturator n., numbness inner thigh, pudendal n
Structural
- Haematoma (on Warfarin)
- Abscess
- Malignanc
- infiltration
- Trauma
Non structural
- Inflammatory
- Diabetes
- Vasculitis
- Radiotherapy
Femoral nerve organisation
Hip flexors, Iliopsoas affected if proximal damage (above inguinal Ligament)
Only knee extension if below inguinal ligament
Distal lesion may produce a pure motor or pure sensory syndrome
Femoral/lateral cutaneous nerves
Femoral N. Weakness
Hip flexion (iliacus)
Knee Extension
Loss of Knee Jerk
Can’t do stairs
Difficulty standing from seated Up stairs, knee buckling
Sensory loss Lat Cut. N. Thigh (relief if seated)
Sensory loss Femoral N
Femoral nerve damage
Sciatica
Pain in sciatic n. distrib (from buttock down leg and can go as far as feet and toes)
Nerve root entrapment (usually L5 / S1)
Differential diagnosis: Hip – pain may radiate not below knee Sacroiliac joints
Causes: Trauma, Haematoma Rarely sciatic nerve compression per se (Piriformis synd) Or misplaced IM injections
Piriformis syndrome
Controversial as to whether muscle compression per se can cause tingling in buttock and down leg (eg after exercise or straining, or prolonged sitting)
Probably may rarely occur in those with anatomical predisposition.
No consensus on criteria Diagnosis of exclusion
Sciatic nerve injury
Apart from:
- Hip flexion
- Knee extension
- Hip adduction
Sciatic nerve or its branches, are motor to virtually all other muscle groups in the leg
Isolated Hip fracture – sciatic n. Pelvic/ sacral fracture – sacral plexus)
What can sciatic nerve damage look like?
Partial sciatic n. damage can look like Common peroneal or Tibial n. damage
Tibial nerve
Behind knee
- Can’t stand on tiptoes
- Weak foot inversion
- Painful numb sole
Causes:
- Trauma: Haemorrhage
- Bakers cyst
- Nerve tumour
- Entrapment by the tendinous arch at the soleus muscle.
In the popliteal fossa the nerve gives off branches to gastrocnemius, popliteus, soleus and plantaris, and the sural nerve.
Tibial N.- lower leg/ ankle
tibialis posterior, flexor digitorum longus, flexor hallucis longus Intrinsic foot muscles
Tarsal Tunnel
Sole pain worse standing/ walking Not heel pain Differential Morton’s neuroma
Sural nerve
Sural nerve - superficial, sensory
Used in nerve biopsies
Easy because superficial
doesnt give loss of function as only sensory
Common peroneal nerve
May also be damaged by tight plaster casts, leg crossing
Weight loss- slimmers palsy
Sensory loss -dorsum of foot and outer aspect lower leg
Weakness of -dorsiflexion and eversion of foot
Neurogenic foot drop
- Upper motor neuron (brain/ spinal cord)
- Conus
- L4/L5
- Cauda equina
- Sacral plexus
- Sciatic n.
- Common peroneal n.
Polyneuropathy
Polyneuropathy – generalised relatively homogeneous process affecting many peripheral nerves with the distal nerves affected most prominently.
Peripheral neuropathy – refers to any disorder of the peripheral nervous system including radiculopathies and mononeuropathies
Distribution of peripheral neuropathy
Length dependent polyneuropathy
Common causes (Toxic/metabolic)
- Diabetes
- Alcohol
- B12 def
- Chemotherapy
- Idiopathic
Clinical symptoms
- Numbness, paraesthesia, weakness
- Pain
Non-length dependent polyneuropathy
Guillian Barre syndrome
Named after French Neurologists in 2016
Also known as Acute inflammatory demyelinating polyneuropathy
Immune response to a preceding infection
Rapidly progressive (days to weeks) weakness including limbs, facial, respiratory and bulbar muscles
Absent reflexes
Neuronopathy
Form of polyneuropathy
Disorders that affect specifically population of neurons.
Motor neuronopathy
- Site of damage: Anterior horn cell
- Causes: ALS, Polio
Sensory neuronopathy
- Site of damage : Dorsal root ganglion
- Causes: Sjogrens syndrome, Paraneoplastic
Polyradiculopathy
Affects multiple nerve roots.
Causes:
- Spinal stenosis: Cervical, lumbar
- Cancer: Leptomeningeal metastases
- Infection: Lyme, HIV,
Types of peripheral neuropathy
Shin splints
Muscle bulk increases 20% during exercise and contributes to the transient increase in intracompartmental pressure
Anterior and lateral compartments of the lower leg are commonly affected
Generally causes pain on and post exercise- AKA Shin Splints
Manage with RICE (rest / cooling – ice)
What is compartment syndrome?
Increase in pressure within a myofascial compartment which has limited ability to expand
May be acute or chronic
Acute compartment syndrome is a surgical emergency
Where does CS occur?
Any limb compartment
Commonest Lower leg Forearm
Also Hand Foot
why leg?
What causes CS?
Fractures (1-6% Tibial Fractures)
Crush Injuries
Burns
Electric Shock
Fluid Injection
Drugs • Warfarin/other anticoagulants • Anabolic Steroid use • Iv drug use
Disease - Haemophilia
External Causes - Tight splints/casts, Tourniquet
Consequences of CS
Tissue perfusion is proportional to the difference between the capillary perfusion pressure and the interstitial fluid pressure
elevated compartment pressure causes muscle and nerve ischemia
Untreated, within 6-10 hours, the final result is muscle infarction, tissue necrosis, and nerve injury
Certain tissues are more sensitive than others and this can be a clue to diagnosis Sensory nerves
Acute anterior CS leg
Dorsiflexion muscles of ankle and foot Tibialis anterior, Extensor digitorum longus Extensor hallucis longus, Peroneus tertius
Anterior tibial artery Commonly injured in lateral tibial plateau fractures
Deep peroneal nerve Sensation to the first dorsal web space
Acute posterior CS leg
What are the signs of CS?
Pain! (out of proportion to the original injury)
Pain +++ on passive stretching
Tense limb
Decreased function of the compartment muscles
Distal neurologic compromise
Reduced distal pulses
Investigation for compartment syndrome
Clinical suspicion is all important
Measuring of intra-compartmental pressures can be useful
Creatine kinase (CK) of 1000-5000 U/mL
Myoglobinuria
Management of acute CS
Genuine confirmed CS is an emergency
Often surgery is required
Aim is to lay open the myofascial compartment and diminish intra-compartmental pressure
External causes
Tight casts/ splints Dressings
Treatment of compartment syndrome
Fasciotomy
incision in skin and fascia to release pressure
vessels become no longer compressed, capillaries become functional
Complications of management
If fasciotomy is performed within 25-30 hours following onset of acute CS, the prognosis is good
Little or no return of function can be expected when diagnosis and treatment are delayed
Rhabdomyolysis - Renal Failure
Limb Loss
