The common peroneal nerve arises from the Sciatic nerve and carries somatomotor and general somatosensory fibers from the L4-S2 roots.
Course
The common peroneal nerve initially runs medial to the biceps femoris muscle, providing motor innervation to its short head. It then passes around the head of the fibula and into the fibular compartment, where it divides into its two terminal branches, the superficial peroneal nerve and the deep peroneal nerve.
Clinical features
Damage to the common peroneal nerve causes paralysis of the fibular muscles, which pronate the foot, as well as the extensors of the lower leg. The foot is therefore plantarflexed and supinated. This position is also referred to as an equinovarus foot. Loss of innervation to the dorsiflexors of the foot results in the clinical picture of Steppage gait.
Imaging
MRI
On MRI imaging, the common peroneal nerve is best visualized on an axial T1-weighted sequence[^1].