A 40 yr old pedestrian hit by a car and has suffered a fracture to the proximal fibula. On examination, it is noted that he has foot drop and reduced sensation over the lateral lower leg and lateral dorsum of the foot. Which nerve has been damaged as a complication of this fracture?
a. sciatic nerve
b. common fibular (peroneal) nerve
c. tibial nerve
d. popliteal nerve
e. posterior femoral cutaneous nerve
Just above the popliteal fossa, the sciatic nerve divides into the common fibular (peroneal) nerve and the tibial nerve (see figure below). The common fibular nerve exits the popliteal fossa and curls around the lateral leg just below the head of the fibula where it is susceptible to injury in fibular neck fractures.
Once it is anterior to the upper fibula the common fibular nerve gives off two branches. One is the superficial fibular (peroneal) nerve which innervates the muscles of the lateral compartment of the lower leg (fibularis longus and brevis) to evert and weakly plantarflex the foot. The other is the deep fibular (peroneal) nerve which supplies the muscles of the anterior compartment of the lower leg (tibialis anterior, extensor digitorum longus, extensor hallucis longus and peroneus tertius) which together dorsiflex the foot and extend the toes. Damage to the common fibular nerve, most vulnerable as it winds round the fibular neck, therefore paralyses the anterior compartment muscles leading to foot drop. Foot plantar flexion is largely preserved as the powerful calf plantarflexors – gastrocnemium and soleus – are innervated by the unaffected tibial nerve.
Together, the superficial fibular nerve and the deep fibular nerves also supply sensation to the lateral lower leg and lateral dorsum of the foot.