Nerve Injuries in the Lower Limb

Question 1

Structure a nerve’s microstructure and then on a slightly bigger scale.

Answer 1

The cell body contains the nucleus and has projections which are dendrites, then gives off the axons which are surrounded by the myelin sheath (except at the nodes of Ranvier) and a synaptic knob at the end.
A peripheral nerve is made of multiple fascicles covered in epineurium, with each radicle surrounded by perineurium and containing many myelinated nerve fibres, covered by endoneurium.

Question 2

What are the different types of nerve injuries (as in how they are injured)?

Answer 2

Loss of function - motor/sensory/proprioception or Neuroma formation leading to pain (swelling/bundle where a nerve is cut).

Question 3

Sedon’s grades of nerve injury may Class them as a axonotmesis, a neurotmesis or a neurapraxia; explain what these are in order from least to most severe.

Answer 3

Neurapraxia is just conduction block (no myelin sheath),
Axonotmesis is where the axons are divided and
Neurapraxia involves the whole nerve divided (myelin sheath and axon).

Question 4

Which nerves provide motor supply to the lower limbs (just 4 main ones)?

Answer 4

The Femoral nerve and its branches, the Sciatic nerve and its branches, the Obturator nerve and the superior gluteal nerve.

Question 5

Describe the sensory supply to the thigh.

Answer 5

Thigh - femoral nerve supplies anteromedial, the Obturator nerve does a medial patch, lateral cutaneous nerve of thigh and posterior cutaneous nerve of thigh.

Question 6

Describe the sensory supply to the leg and foot.

Answer 6

Saphenous nerve (from femoral) does the medial part, common perineal does superior lateral, with its superficial branch supplying the inferior lateral and most of the dorsum and its deep branch supplying the first web space, sural nerve does posterior lateral, down to tiny bit of sole and tibial does heel.

Question 7

What might cause a neuropathy?

Answer 7

Stretch injury of nerve or complete division, extrinsic pressures (tumour, abscess etc), medical conditions (diabetes, alcohol excess, drugs) and other rarer causes, such as nerve tumours.

Question 8

Describe the repair process of a severed nerve, over time including how it comes to a successful/unsuccessful outcome.

Answer 8

Inflammatory cells work distal to the injury (Wallerian degeneration of myelin and fibre), then 3 weeks after, proliferation of Schwann cells with a axonal sprouts being guided by it, can lead to successful nerve (and so muscle after atrophy) regeneration at 3 months, or not if disorganised axonal sprouts (leading to a Neuroma). It may grow 1-2mm a day.

Question 9

Myotomes of the lower limb:
L2 ...
L3 ...
L4 ...
L5 ...
S1 ...
S2 ...

Answer 9

L2 - hip flexion,
L3 - knee extension and hip adduction,
L4 - ankle dorsiflexion,
L5 - great toe extension, inversion and hip abduction,
S1 - ankle plantar flexion, ankle eversion, hip extension,
S2-knee flexion and great toe flexion.

Question 10

What are the myotomes of the upper limb, according to the Thriller dance?

Answer 10

C5 - elbow flexion, shoulder abduction,
C6 - supination and wrist extension,
C7 - pronation and elbow extension,
C8 - digit and thumb flexion
T1 - digit abduction.

Question 11

What are the dermatomes of the lower limb?

Answer 11

L1 is the upper groin, L3 is the knee and medial thigh with L2 between them.
L4 is the medial leg, L5 the lateral anterior leg and medial dorsum.
S1 is lateral dorsum and heel and S2 is posterior thigh and the upper 1/2 of the posterior leg.

Question 12

How can you tell if a prolapsed disc has injured L4, L5 or S1?

Answer 12

L4 - weakened anterior tibialis (Dorsi flexion), knee jerk reflex and sensation in the medial leg (its dermatome).
L5 - extensor hallicus longus is weak and dermatome of lateral anterior leg and medial dorsum.
S1 - weakened gastroc-soleus complex, ankle jerk reflex and dermatome of lateral dorsum and heel.

Question 13

The Sciatic nerve is the ___________ in the body, supplying most of the lower limb. It exits the Sciatic ______ anterior to the ___________, but posterior to the short external _______. Then it runs down the thigh between the adductor ________ and the ______ head of biceps femoris. In the popliteal fossa, it bifurcates into the tibial and _________ ___________ nerves (there are variants).

Answer 13

Largest
Notch
Piriformis
Rotators
Magnus
Long
Common peroneal

Question 14

What is Piriformis syndrome?

Answer 14

A condition with Sciatica symptoms, but from injury of the peripheral nerve, not spinal cord or spinal nerves. It may be due to overuse of the muscle causing spasm. The treatment is mostly activity modification.

Question 15

Which ligament is described below?
From the lateral border of the psoas major, across the iliac fossa to pierce the inguinal ligament, it travels in a fibrous tunnel medial to the ASIS and enters the thigh deep to the fascia lata before continuing to subcutaneous tissues.
Also, when does it divide?

Answer 15

The lateral cutaneous nerve of the thigh - it divides just distal to the inguinal ligament into anterior and posterior branches to supply the anterolateral aspect of the thigh.

Question 16

What is Meralgia paraesthetica?

Answer 16

Compression of the lateral cutaneous nerve of the thigh as it passes through the inguinal ligament or as it pierces the fascia lata. Perhaps from obesity, pregnancy or tight clothing. A burning/stinging sensation results, over the anterolateral aspect of the thigh.

Question 17

Meralgia paraesthetica can be felt with tenderness on palpation and reduced sensation, how is it aggravated and relieved?

Answer 17

Walking or standing aggravates it and it is relieved by lying with a flexed hip.

Question 18

Local nerve blocks are restricted when treating Meralgia paraesthetica, but local nerve blocks can be beneficial, how is the diagnosis reached?

Answer 18

Absence of motor signs and exclusion of pelvic or intra-abdominal causes of the irritation.

Question 19

What is the result of an injury to femoral nerve?

Answer 19

Weakness of the quadriceps (so knee extension) and hip flexors, as well X loss of the saphenous nerve and medial cutaneous nerve of the thigh for sensation. (+ sartorius abducts and pectineus adducts) - it supplies the ANTERIOR compartment of the thigh.

Question 20

The tibial nerve is the larger terminal branch of the Sciatic nerve, where does it travel after the bifurcation?

Answer 20

It crosses the popliteal fossa and passes deep to the soleus. In the posterior compartment it runs between the flexor digitorum longus and the flexor hallucis longus (lateral), then passes deep to the flexor retinaculum and gives off the medial calcaneal nerve (sensory heel innervation), then divides into medial and lateral plantar nerves to give sensory innervation to the sole.

Question 21

Injury to the tibial nerve is relatively unlikely because it is well padded by muscles on multiple sides, what is noticed if it is injured?

Answer 21

Loss of the posterior leg compartments, so weakness of plantar flexion and inversion, leading to unopposed Dorsi flexion and eversion, hence a calcaneovalgus posture. Also, loss of plantar sensation (not medial and lateral sides innervated by the saphenous and sural nerves).

Question 22

A common peroneal nerve injury will compromise the functions in the lateral and anterior compartments of the leg, what will be noticed?

Answer 22

Loss of ankle everters and Dorsi flexors, as well as loss of sensation on the lateral leg and dorsum. (Affects superficial and deep)

Question 23

What is noticed in the case of a superficial peroneal nerve injury?

Answer 23

Motor innervation to peroneus longus and brevis (lateral) is compromised, so weakness in eversion. Also lost is sensation in the anterolateral calf and dorsum (not the first web space).

Question 24

What could cause injury to the superficial peroneal nerve?

Answer 24

The cause may be ankle surgery via a lateral approach or ankle arthroscopy portal placement.

Question 25

Deep peroneal nerve injuries affect the anterior muscles of the leg, what should be expected in this case?

Answer 25

Tibialis anterior, extensor hallicus longus and extensor digitorum longus (and peroneus tertius, usually present) are the anterior muscles. Weakness in ankle Dorsi flexion can lead to foot drop and there is also sensory loss in the first webspace.

Question 26

A saphenous nerve injury may be obtained from stripping of the long saphenous vein, if it has varicosities, because they run alongside each other. What is experienced if this happens?

Answer 26

Loss of sensation over the medial leg.

Question 27

The sural nerve is made of branches from the peroneal and tibial nerves and injury can cause loss of sensation to the lateral side of the sole of the foot. How could it be injured?

Answer 27

Perhaps from surgical injury during a posterior approach to the ankle, Achilles’ tendon, short saphenous vein or it is useful when taken for a nerve graft.