MSK 13 - Lower Limb Nerve Injuries

Question 1

What are the 3 types of nerve injury according to the Seddon classification?

Answer 1

1) Neuropraxia - a conduction block
2) Axonotmesis - axons divided but neural sheath still in-tact
3) Neurotmesis - most severe, nerve is completely divided

Question 2

What are the consequences of nerve injuries?

Describe the process of nerve regeneration

Answer 2

• Loss of function (motor, sensory + proprioception) + neuroma formation (growth of nerve tissue, typically benign) leading to pain.

1) Inflammatory cells move into injured area, gradually complemented by macrophages
2) Wallerian degeneration - nerve endings distal to injury start degenerating
3) Schwann cells proliferate from target organ trying to reach cell body
4) Can have successful outcome where nerve joins up successfully with injured part or poor outcome where Schwann cells fail to meet injured nerve, leading to neuroma formation.

Question 3

How do you work out the clinical presentation of a nerve root injury due to a prolapsed vertebral disc?

Answer 3

• The lumbar nerve roots emerge from below their vertebrae, e.g.: L4 from L4/L5 level.
• The most common sites for a slipped risk are L4/5 and L5/S1 (so L4 + L5 nerve roots).
• The presentation depends on what the nerve root innervates (use myotomes + dermatomes), e.g.: L4 nerve root compression leads to loss of ankle dorsiflexion + numbness in the L4 dermatome.

Question 4

Describe the course of the sciatic nerve

Answer 4

• Exists sciatic notch anterior to piriformis, posterior to short external rotators, travels between adductor magnus and the long head of the biceps femoris. Bifurcates into the tibial and common peroneal (fibular) branch in the popliteal fossa.

Question 5

What is piriformis syndrome?

Answer 5

• Piriformis syndrome is sciatica-like symptoms but not due to compression of spinal nerve roots, instead compression of the sciatic nerve via the piriformis muscle (overuse of muscle leads to spasm)
• Symptoms = dull ache in buttock, typical sciatica pain in thigh/leg/foot, pain walking up stairs, reduced ROM at hip joint.

Question 6

Describe the course of the lateral cutaneous nerve of the thigh.

Answer 6

• Passes from the lateral border of the psaos major across the iliac fossa to pierce the inguinal ligament.
• Enters thigh deep to fascia lata before becoming superficial 10cm below the inguinal ligament
• Supplies anterolateral aspect of thigh

Question 7

What is meralgia paraesthesia?

What are the associated symptoms?

Answer 7

• Compression of the lateral cutaneous thigh nerve as it passes through inguinal ligament or pierces fascia lata.
• Caused by obesity (compression by abdominal fat), tight clothing, pregnancy
• Burning or stringing sensation in anterolateral aspect of thigh
• Aggravated by walking/standing, relieved by lying down/hip flexion.

Question 8

How is diagnosis of meralgia paraesthesia confirmed?

Answer 8

• Confirmed by absence of motor signs and by excluding pelvis/intra-abdominal causes of irritation such as a tumour

Question 9

Describe the course of the femoral nerve + the structures it innervates.

Answer 9

• Arises from L2/3/4 in lumbar plexus, enters femoral triangle by passing beneath inguinal ligament. Divided into multiple branches 4cm below inguinal ligament.
• Innervates anterior thigh muscles that flex the hip and extend the knee. Sensory distribution is to the anteromedial thigh and medial side of the leg and foot.
• Injury depends on muscle affected, e.g.: paralysis of the iliacus will affect flexion of the hip etc.

Question 10

What is Trendelenburg sign?

What are the causes?

Answer 10

• Pelvis drops on unaffected side when weight beared on injured side. Weak abductors on affected side, other side drops to compensate.
• Injury to superior gluteal nerve - e.g.: L5 radiculopathy
  (as SGN arises from S5-L1 roots) or surgical trauma during total hip replacement.

Question 11

Describe the course of the tibial nerve

Answer 11

• Larger terminal branch of the sciatic nerve, crosses popliteal fossa, passes deep to soleus.
• Lies between the flexor digitorum longus and flexor hallucis longus
• At the ankle passes beneath flexor retinaculum and gives off the medial calcaneal branch to the heel.
• Divides into medial and lateral plantar nerves

Question 12

What are the consequences of tibial nerve injury?

Answer 12

• Loss of posterior leg compartments - loss of active plantar flexion + inversion.
• Loss of plantar sensation except medial and lateral sides supplied by saphenous and sural nerves.

Question 13

What are the consequences of common peroneal (fibular) nerve injury?

What are the consequences of superficial peroneal (fibular) nerve injury?

What are the consequences of deep peroneal (fibular) nerve injury?

Answer 13

• Paralysis of ankle everters and dorsiflexors
• Loss of sensation lateral lower leg and dorsum of foot
• Patient presents with foot drop due to paralysis of tibialis anterior + inversion of the ankle due to paralysis of peroneus longus/brevis.
• Loss of ankle eversion (peroneus/fibularis longus + brevis paralysed) + sensory loss to anterolateral lower leg and dorsum of foot (sparing 1st dorsal web space)
• Loss of ankle dorsiflexion due to paralysis of 4 x ankle dorsiflexors (foot drop) and sensory loss in 1st dorsal web space.

Question 14

When can saphenous nerve injury occur?

What are the consequences of saphenous nerve injury?

Answer 14

• Injured during venous cut-down (to obtain venous access in emergency) and occasionally during varicose vein stripping.
• Loss of sensation to medial leg and ankle and sometimes medial border of foot.

Question 15

What is the consequence of sural nerve injury?

Answer 15

Loss of sensation to sole of foot (very lateral side)