18. Lower limb nerve injuries

Question 1

Cauda equina vs conus lesions

Answer 1

Conus medullaris - upper motor neuron L1/2 mix Cauda equina - lower motor neuron

Question 2

Landmarks for lumbar puncture

Answer 2

Question 3

Cauda equina vs conus medullaris

Answer 3

Question 4

Cauda equina causes

Answer 4

Disc herniation, spinal fracture, tumour

Question 5

Conus medullaris infections

Answer 5

Disc herniation, tumour

Inflammatory conditions

• chronic inflammatory demyelinating polyradiculopathy
• Sarcoidosis

Infection

• CMV, HSV, EBV, Lyme, TB

Question 6

L5/S1 disc herniation effect

Answer 6

Compression of cauda equina

Deformity of thecal sac impinging on the cauda equina

Question 7

Nerve root entrapment - sciatica

Answer 7

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)

Question 8

Lower limb root lesions - reflex and sensory loss (dermatomes)

Answer 8

Question 9

Lower limb root lesions - weakness

Answer 9

Question 10

Lumbar plexus

Answer 10

Question 11

Sacral plexus

Answer 11

Question 12

Lumbrosacral plexus regions

Answer 12

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

Question 13

Femoral nerve organisation

Answer 13

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

Question 14

Femoral/lateral cutaneous nerves

Answer 14

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

Question 15

Femoral nerve damage

Answer 15

Question 16

Sciatica

Answer 16

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

Question 17

Piriformis syndrome

Answer 17

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

Question 18

Sciatic nerve injury

Answer 18

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)

Question 19

What can sciatic nerve damage look like?

Answer 19

Partial sciatic n. damage can look like Common peroneal or Tibial n. damage

Question 20

Tibial nerve

Answer 20

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.

Question 21

Tibial N.- lower leg/ ankle

Answer 21

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

Question 22

Sural nerve

Answer 22

Question 23

Sural nerve - superficial, sensory

Answer 23

Used in nerve biopsies

Easy because superficial

doesnt give loss of function as only sensory

Question 24

Common peroneal nerve

Answer 24

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

Question 25

Neurogenic foot drop

Answer 25

* Upper motor neuron (brain/ spinal cord) * Conus * L4/L5 * Cauda equina * Sacral plexus * Sciatic n. * Common peroneal n.

Question 26

Polyneuropathy

Answer 26

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

Question 27

Distribution of peripheral neuropathy

Answer 27

Question 28

Length dependent polyneuropathy

Answer 28

Common causes (Toxic/metabolic) * Diabetes * Alcohol * B12 def * Chemotherapy * Idiopathic Clinical symptoms * Numbness, paraesthesia, weakness * Pain

Question 29

Non-length dependent polyneuropathy

Answer 29

Question 30

Guillian Barre syndrome

Answer 30

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

Question 31

Neuronopathy

Answer 31

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

Question 32

Polyradiculopathy

Answer 32

Affects multiple nerve roots. Causes: * Spinal stenosis: Cervical, lumbar * Cancer: Leptomeningeal metastases * Infection: Lyme, HIV,

Question 33

Types of peripheral neuropathy

Answer 33

Question 34

Shin splints

Answer 34

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)

Question 35

What is compartment syndrome?

Answer 35

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

Question 36

Where does CS occur?

Answer 36

Any limb compartment Commonest Lower leg Forearm Also Hand Foot

Question 37

why leg?

Answer 37

Question 38

What causes CS?

Answer 38

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

Question 39

Consequences of CS

Answer 39

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

Question 40

Acute anterior CS leg

Answer 40

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

Question 41

Acute posterior CS leg

Answer 41

Question 42

What are the signs of CS?

Answer 42

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

Question 43

Investigation for compartment syndrome

Answer 43

Clinical suspicion is all important Measuring of intra-compartmental pressures can be useful Creatine kinase (CK) of 1000-5000 U/mL Myoglobinuria

Question 44

Management of acute CS

Answer 44

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

Question 45

Treatment of compartment syndrome

Answer 45

Fasciotomy incision in skin and fascia to release pressure vessels become no longer compressed, capillaries become functional

Question 46

Complications of management

Answer 46

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