Peroneal Tunnel Syndrome

Often extrinsic compression of the common peroneal nerve at the fibular head with lateral leg pain, and if severe, foot drop.

Peroneal Tunnel Syndrome: Anatomy

Typically, the common peroneal nerve arises as a branch from the sciatic nerve near the proximal margin of the popliteal fossa
The nerve runs with the biceps femoris muscle and tendon into the popliteal fossa, at which point the nerve encircles the head of the fibula, where it is covered only by subcutaneous tissue over a length of approximately 4 cm
The common peroneal nerve then passes below the tendinous origin of the peroneus longus and enters the peroneal tunnel near the fibular neck
The lateral sural cutaneous nerve branches from the common peroneal nerve just proximal to the fibular head
As the common peroneal nerve enters the peroneal tunnel, it divides into deep motor, superficial sensory and recurrent peroneal nerves
In the peroneal tunnel, the peroneal nerve and its branches stretch over the fibular neck and are covered by the tendinous origin of the peroneus longus muscle
The superficial peroneal nerve supplies the peroneus brevis and longus muscles
At the junction of the mid- and distal third of the tibia, the superficial peroneal nerve pierces the lateral fascia and splits into two cutaneous branches
The deep peroneal nerve innervates the muscles of the anterior compartment, including the tibialis anterior, the extensor digitorum longus and the extensor hallucis longus¹

Peroneal Tunnel Syndrome: Etiology

Compression at the site of fascial penetration produces the syndrome of the superficial peroneal nerve with secondary varus deformity due to unopposed inverters of the foot and sensory loss over the anterolateral calf and dorsum of the foot
Adduction, supination and plantar flexion of the foot serve to tense the peroneus longus muscle and bring it closer to the fibula, thereby decreasing the space within the peroneal tunnel and compressing the common peroneal nerve against the fibular neck
Repetitive actions which require inversion or pronation such as with runners and machine operators using pedals can stretch the common peroneal nerve against the fibular neck at the lower margin of the tendinous arch of the peroneus longus muscle
Internal causes include bony changes, such as exostosis, osteophyte or proximal fibular fracture, as well as lipoma, ganglia and synovial cysts
Etiologies for peroneal tunnel syndrome include external compression, such as plaster casts, prolonged crossed legs, or certain sleeping positions¹

Peroneal Tunnel Syndrome: Clinical

Initially, patients present with pain in the region of compression that will eventually spread distally into the common peroneal nerve’s dermatome
Palpation or pressure placed over the site of the tunnel will increase the patient’s pain and thus differentiate this from radiculopathy such as that seen in lumbar stenosis, root entrapment or more proximal compression
Radiation of pain into the thigh may occur¹

Peroneal Tunnel Syndrome: Treatment

Motion training and physical therapy
Arch or fascial release²

Peroneal Tunnel Syndrome: References

Pomeranz SJ. Gamuts & Pearls in MRI & Orthopedics. Ohio, The Merten Company, 1997.
Pomeranz SJ. Orthopaedic and Sports Medicine MRI Volume I: MRI of Entrapment Neuropathies. Ohio, MRI-EFI Publications, 2011.

Peroneal Tunnel Syndrome: Example

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HISTORY:

70-year-old female. Left leg foot drop.

Image 1 - Axial T2 Image 2 - Axial T2

FINDINGS:

Moderate geometric distortion and susceptibility with incomplete fat suppression related to prosthesis. No evidence for patellar fracture. No loosening or migration of patellar struts.

No periosteal reaction noted.
No findings to support infection or osteomyelitis.
No surrounding fluid collections or pseudotumors.
Tibiofibular joint intact. Femorotibial alignment maintained.

The peroneal nerve (image 1, green arrow) can be followed normally from just distal to the bifurcation of the sciatic nerve to its location along the posterolateral fibula. At 1.0cm caudal to the fibular tip the peroneal nerve is not visualized (image 2, green arrow) with certainty compatible with either axonotmesis or neurotmesis. Consider possible attenuation from a stretching injury. Moderate fatty infiltration noted involving the anterior compartment muscles. Moderate fatty infiltration also noted involving the distal vastus lateralis.

CONCLUSION:

1. The peroneal nerve can be followed normally from just distal to the bifurcation of the sciatic nerve to its location along the posterolateral fibula. At 1.0 cm caudal to the fibular tip the peroneal nerve is not visualized with certainty compatible with either axonotmesis (injury to peripheral nerve of an extremity of body) or neurotmesis (serious nerve injury where both nerve and nerve sheath are disrupted).

2. Moderate fatty infiltration noted involving all the anterior compartment muscles and distal fibers of the vastus lateralis. Consider early denervation changes.
3. No findings noted supporting diagnosis of osteomyelitis, fracture, hardware failure, surrounding fluid collection, or pseudotumor.
4. May see above for additional findings and pertinent negatives.