Lower limb nerve injuries and compartment syndrome

Question 1

Pain severity

Answer 1

Cauda equina

• radicular
• more severe

Conus medullaris
- less severe

Question 2

Location of pain

Answer 2

Cauda equina

• unilateral/ asymmetric
• perineum, thighs and legs

Conus medullaris

• bilateral
• perineum, thighs

Question 3

Sensory disturbance

Answer 3

Cauda equina

• saddle
• unilateral/ asymmetric

Conus medullaris
- bilateral saddle distribution

Question 4

Motor loss

Answer 4

Cauda equina

• asymmetric
• atrophy

Conus medullaris
- symmetric

Question 5

Reflexes

Answer 5

Cauda equina
- ankle and knee reduced

Conus medullaris
- ankle only reduced

Question 6

Bowel/ bladder

Answer 6

Cauda equina
- late

Conus medullaris
- early

Question 7

Sexual function

Answer 7

Cauda equina
- impaired- less severe

Conus medullaris
- impaired- more severe

Question 8

Causes of pain

Answer 8

Cauda equina
- disc herniation, spinal fracture, tumours

Conus medullaris

• disc herniation, tumour
• inflammatory conditions (chronic inflammatory demyelinating, polyradiculopathy, sarcoidosis)
• infection (CMV, HSV, EBV, lyme, TB)

Question 9

Nerve root entrapment- ‘sciatica’

Answer 9

Compression

• disc: posterior central, lateral
• bone: osteophyte
• ligaments
• small canal: stenosis

Sciatica- usually L5, S1 nerve root impingement

Pain may be felt in dermatome (sharp/ superficial) or myotome (deep ache)

Question 10

Lower limb root lesions- reflex and sensory loss

Answer 10

Lower limb dermatome more variable than upper limb

L1 inguinal area
L2 front of thigh
L3 front of knee
L4 from- inner/ medial leg
L5 outer leg, dorsum of foot, inner sole
S1 little toe, rest of sole, back of leg
S2 thigh to top of buttock
S3-5 concentric rings around anus/ genitalia 

Knee jerk L4
Ankle jerk S1

Question 11

Lower limb root lesions- weakness

Answer 11

L1/2- hip flexion

L3/4- knee extension

L4- foot inversion

L5- knee flexion, ankle dorsiflexion, toe extension, foot inversion and eversion

S1- knee flexion, ankle plantar flexion, toe flexion, foot eversion

Question 12

Lumbosacral plexus lesions

Answer 12

Childbirth (large head, prolonged labour)- esp obturator, numbness inner thigh, pudendal nerve

Structural

• haematoma
• abscess
• malignancy
• 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 nerve weakness
Hip flexion
Knee extension
Loss of knee jerk
Can't do stairs

Sensory loss- femoral nerve

Saphenous (sensory branch of femoral nerve)

Question 15

Femoral nerve damage

Answer 15

Surgery

Gynae procedures, esp hysterectomy, femoral artery bypass/ puncture

Question 16

Sciatica

Answer 16

Pain in sciatic nerve distribution

Nerve root entrapment (usually L5/S1)

Question 17

Differential diagnosis of sciatica

Answer 17

Hip- pain may radiate, not below knee

Sacroiliac joints

Question 18

Causes of sciatica

Answer 18

Trauma

Haematoma

Rarely sciatic nerve compression

Misplaced IM injections

Question 19

Piriformis syndrome

Answer 19

Controversial as to whether muscle compression can cause tingling in buttock and down leg

Probably may rarely occur in those with anatomical predisposition

Diagnosis of exclusion

Question 20

Sciatic nerve injury

Answer 20

Apart from hip flexion, knee extension, hip adduction

Scaitic nerve or its branches are motor to virtually all other muscle groups in the leg

Isolated hip fracture- sciatic nerve
Pelvic/ sacral fracture- sacral plexus

Question 21

Tibial nerve- behind knee

Answer 21

Can’t stand on tiptoes
Weak foot inversion
Painful numb sole

Causes

• trauma: haemorrhage
• bakers cyst
• nerve tumour
• antrapment by the tendinous arch at the soleus muscle

Question 22

Tibial nerve- lower leg/ ankle

Answer 22

Sole pain worse standing/ walking

Not heel pain

Differential morton’s neuroma

Question 23

Common peroneal nerve

Answer 23

May also be damaged by tight plaster casts, leg crossing, weight loss (slimmers palsy)

Sensory loss- dorsum of foot and outer aspect of lower leg

Weakness of- dorsiflexion and eversion of foot

Question 24

Neurogenic foot drop

Answer 24

Upper motor neuron

Conus

L4/L5

Cauda equina

Sacral plexus

Sciatic nerve

Common peroneal nerve

Question 25

Polyneuropathy

Answer 25

Generalised relatively homogenous process affecting many peripheral nerves with the distal nerves affected most prominently

Question 26

Length dependent polyneuropathy

Answer 26

Common causes - diabetes - alcohol - B12 deficiency - chemotherapy - idiopathic Clinical symptoms - numbness, paraesthesia, weakness - pain

Question 27

Guillain barre syndrome

Answer 27

Acute inflammatory demyelinating polyneuropathy Immune response to a preceding infection Rapidly progressive weakkness including limbs, facial, respiratory and bulbar muscles Absent reflexes

Question 28

Neuronopathy

Answer 28

Form of polyneuropathy Disorders that affect specifically population of neurons Motor neuropathy - sites of damage: anterior horn cell - causes: ALS, polio Sensory neuronopathy - site of damage: dorsal root ganglion - causes: sjogrens syndrome, paraneoplastic

Question 29

Polyradiculopathy

Answer 29

Affects multiple nerve roots Causes - spinal stenosis: cervical, lumbar - cancer: leptomeningeal metastases - infection: lyme, HIV

Question 30

Shin splints

Answer 30

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- shin splints Manage with RICE

Question 31

Compartment syndrome

Answer 31

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 32

Where does compartment syndrome occur?

Answer 32

Any limb compartment Commonest - lower leg - forearm

Question 33

What causes compartment syndrome?

Answer 33

Fractures (1-6% tibial fractures) Crush injuries Burns Electric shock Fluid injection Drugs Disease External causes

Question 34

Consequences of compartment syndrome- physiology

Answer 34

Tissue perfusion is proportional to the difference between the capillary perfusion pressure and the interstitial fluid pressure Elevated compartment pressure causes muscle and nerve ischaemia

Question 35

Consequences of compartment syndrome- pathology

Answer 35

Untreated, within 6-10 hours, the final result is muscle infarction, tissue necrosis, and nerve injury Certain tissues are more sensitive than other and this can be a clue to diagnosis

Question 36

Acute anterior compartment syndrome leg

Answer 36

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 Depp peroneal nerve - sensation to the first dorsal web space

Question 37

Acute posterior compartment syndrome leg

Answer 37

Superficial posterior Plantar flexors of foot - gastrocnemius - plantaris - soleus Sural nerve - sensation to lateral aspect of the foot and distal calf

Question 38

What are the signs of compartment syndrome?

Answer 38

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 39

Investigations for compartment syndrome

Answer 39

Measuring of intra-compartmental pressures can be useful Creatine kinase of 1000-5000 U/ml Myoglobinuria

Question 40

Management of acute compartment syndrome

Answer 40

Genuine confirmed CS is an emergency Often surgery is required Aim is to lay open the myofascial compartment and diminish intra-compartmental pressure