Age / Sex : 19 / M

Chief complaint: Right foot drop after traffic accident (onset: 5 months ago)

What is your impression?

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

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Courtesy: Sang Min Lee, Bundang Medical Center, CHA University

Common peroneal neuropathy with denervation myopathy

Discussion

Findings:

- Thickening of the common peroneal nerve with T2 high signal intensity at the fibular neck level.

- Diffuse fatty atrophy with T2 high signal intensity in the tibialis anterior, extensor digitorum longus, extensor hallucis longus, peroneus longus and brevis muscles.

Differential Diagnosis:

Diagnosis: Common peroneal neuropathy with denervation myopathy

Discussion:

- The CPN (common peroneal neuropathy) is particularly prone to entrapment because it is fixed in position at the greater sciatic foramen (peroneal division) and around the fibular head. There are two common compression sites of the CPN.

- The nerve 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, crush injury, surgery, tumor, osteochondroma, synovial cyst, intraneural and extraneural ganglia, varicosities, aberrant muscle, and prolonged immobilization (Saturday night palsy). Prolonged squatting (strawberry picker’s palsy) and extended lithotomy position due to childbirth or obstetric surgery 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.

- Symptom:

Pain at the site of compression, footdrop, weak foot extension (anterior tibial muscle), weak foot eversion (peroneus longus and brevis muscles), loss of sensation in the lower lateral two-thirds of the leg and the dorsum of the foot