Common fibular nerve

Question 1

Anatomical course

Answer 1

Begins at apex of popliteal fossa.
Follows medial border of biceps femoris and then travels in an inferolateral direction over lateral head of gastrocnemius. At this point it gives rise to 2 cutaneous branches.
Nerve wraps around neck of fibula, passing between attachments of fibularis longus. Here it terminates by dividing into superficial fibular and deep fibular nerves.

Question 2

Motor Innervation

Answer 2

Common fibular nerve - Short head of biceps femoris
Superficial fibular nerve - lateral leg (fibularis longus and brevis)
Deep fibular nerve - anterior leg (tibialis anterior, extensor digitorum longus, extensor hallucis longus, fibularis tertius) and some intrinsic muscles of the foot (extensor digitorum brevis and extensor hallucis brevis)

Question 3

Sensory Innervation of sural nerves (2)

Answer 3

Sural commicating nerve - combines with a branch of the tibial nerve to form the sural nerve which innervates the skin over the lower posterolateral leg.
Lateral sural cutaneous nerve - skin over the upper lateral leg

Question 4

Cause of damage

Answer 4

Fracture of fibula

Tight plaster cast

Question 5

Consequences of damage

Answer 5

Loss of ability to dorsiflex foot at ankle. This causes deformity called footdrop where foot is permanently plantarflexed
Loss of sensation over dorsum of the foot and lateral leg

Question 6

Nerve roots

Answer 6

L4-S3

Question 7

Nerve roots of superficial fibular nerve

Answer 7

L4-S1

Question 8

Anatomical course of superficial fibular nerve

Answer 8

Arises in neck of fibula, descending between fibularis muscles and lateral side of extensor digitorum longus. Here it gives rise to motor branches which supply fibularis longus and brevis.
Continues descent with purely cutaneous function.
When it reaches the lower third of leg it pierces the deep crural fascia and terminates by dividing into medial and intermedial dorsal cutaneous nerves which enter the foot.

Question 9

Sensory Innervation of superficial fibular nerve

Answer 9

Cutaneous branches - anterolateral leg
Medial and intermedial dorsal cutaneous nerves - dorsum of foot (except webbed space between hallanx and 2nd digit)
Dermatomes L5 and S1

Question 10

Cause of superficial fibular nerve entrapment (nerve compression)

Answer 10

Ankle sprains or twisting of the ankle - This stretches the nerve
Compression by deep fascia of leg as the superficial fibular nerve exits it (requires surgical decompression of nerve)

Question 11

Consequence of superficial fibular nerve entrapment

Answer 11

Pain and paresthesia over lower leg and dorsum of foot

Question 12

How is superficial fibular nerve damaged

Answer 12

Fracture of fibula

Perforating wound to lateral leg

Question 13

Nerve roots of deep fibular nerve

Answer 13

L4-5

Question 14

Anatomical course of deep fibular nerve

Answer 14

Arises in superolateral leg between fibularis longus and neck of fibula
(Follows the course of anterior tibial artery) travels in inferomedial direction passing between the tibialis anterior and extensor digitorum longus
It crosses the ankle joint, passing anterior to distal tibia and deep to extensor retinaculum.
It terminates in dorsum of foot where it divides into lateral and medial branches

Question 15

Consequence of deep fibular nerve entrapment/compression

Answer 15

Paralysis of anterior leg muscles so patient can’t dorsiflex foot (footdrop)

Question 16

Consequence of footdrop

Answer 16

Difficulty clearing ground during swing phase
Limb looks too long
Foot slaps down on floor when patient walks (can’t be lowered in controlled manner)
Develop abnormal gait

Question 17

Types of abnormal gait with footdrop

Answer 17

Waddling gait - patient leans excessively onto normal limb
Swing out gait - patient abducts abnormal limb
High steppage gait - patient flexes hip and knee excessively on abnormal limb

Question 18

Causes of deep fibular nerve entrapment/compression

Answer 18

Excessive use of anterior leg muscles - compression within anterior compartment
Tight fitting shoes - compression beneath extensor retinaculum