Age / Sex : 30 / M

Chief complaint: Left lower leg pain after jumping 

1) What is your impression?

Two weeks later, you can see the final diagnosis with a brief discussion of this case.

(Quiz는 quiz일 뿐이오니 답안은 한 개만 보내주시기 바랍니다)

Courtesy: 최윤선(Yun Sun Choi), 을지대 을지병원(Eulji Hospital, Eulji University)

Common peroneal neuropathy

Discussion

Findings:

Axial T2-weighted fat-suppressed and T1-weighted MR images show denervation edema and fatty infiltration of the anterolateral compartment muscles, predominantly the anterior tibial and peroneus longus muscles. The superficial and deep peroneal nerves are slightly large.

Differential Diagnosis:

1. compartment syndrome

2. shin splint

3. stress fracture

Diagnosis: Common peroneal neuropathy

Discussion:

The common peroneal nerve (CPN) descends obliquely to wind around the neck of the fibula before it enters the per­oneal tunnel. The CPN trifurcates into the recurrent articular branch, superficial peroneal nerve (SPN), and deep peroneal nerve (DPN). This trifurcation most commonly occurs at or distal to the fibular neck but can also occur above or up to 3 cm below the knee joint. The SPN supplies the lateral compartment muscles (peroneus longus and brevis) and the DPN supplies the anterior compartment muscles (anterior tibialis, extensor hallucis longus, extensor digitorum longus and brevis, peroneus tertius).

Common peroneal neu­ropathy is the most common mono-neuropathy in the lower extremity. In most cases, CPN neuropa­thy occurs in the knee region, whereas neuropathy of the SPN and DPN occurs more distally in the leg, ankle, or foot. The CPN may be compressed as it crosses the fibular neck, owing to its superficial location, or as it travels under the origin of the peroneus longus muscle. Injury to the nerve at these locations may be the result of extrin­sic compression, stretch injury, or direct trauma. Extrinsic compression of the CPN can be the result of external compression by various agents such as short-leg cast, sur­gery, osteochondroma, synovial cyst, intraneural and extraneu­ral ganglia, varicosities, and aberrant muscle. Prolonged squatting and extended lithotomy position due to childbirth will typi­cally produce bilateral CPN entrapment. Diabetic patients are at an increased risk for entrapment of the CPN within the fibrous tunnel underneath the peroneus longus muscle. Severe ankle sprain with sudden flexion and inversion of the foot predisposes the CPN to a stretch injury.

The clinical symptoms and signs are foot drop, slapping gait, and loss of sensation in the lower lateral two thirds of the leg and dorsum of the foot. EMG studies are reliable in detecting common peroneal neuropathy and are essential in distinguishing it from more proximal compression of either the sciatic nerve or the peroneal division of the sciatic nerve.             On axial fluid-sensitive MR images at the knee joint, the proximal portion of the nerve is relatively large and hyperintense. Tumor, varicosities, ganglion, popliteal artery aneurysm, and anomalous muscle can exert mass effect on the nerve may be detected. In direct signs of common peroneal neuropathy include denervation edema and atrophy of both the anterior compartment and the lateral compartment. MRI can play an important role in evaluating chronic leg pain in the athlete and in differentiating CPN entrapment from other common causes of chronic leg pain, including stress fracture, chronic exertional compartment syndrome, and popliteal artery entrapment syn­drome.   

References:

1. Stoller DW, Rosenberg ZS, Cavalcanti C, et al. Entrapment neuropathies of the lower extremity. In: Stoller DW, ed. Magnetic Resonance Imaging in Orthopaedics and Sports medicine. Philadelphia, PA: Lippincott Williams & Wilkins;2007:1072-1076

2. Beltran LS, Bencardino J, Ghazikhanian V, Beltran J. Entrapment neuropathies III: lower limb. Semin Musculoskelet Radiol 2010;14:501-511

3. Donovan A, Rosenberg ZS, Cavalcanti CF. MR imaging of entrapment neuropathies of the lower extremity. Part 2. The knee, leg, ankle, and foot. Radiographics 2010;30(4):1001-1019