Common Peroneal Nerve Lesions

The common peroneal nerve provides:

• Motor innervation to the lateral compartment of the leg
• Sensory innervation to the lateral leg and dorsum of the foot

Injury typically results in foot drop due to loss of dorsiflexion.

Most vulnerable at the neck of the fibula, especially with tight plaster casts in this region — a common cause of neuropraxia.

Anatomy

Course of the common peroneal nerve

• Originates with the tibial nerve from the sciatic nerve in the lower posterior thigh
• Runs along biceps femoris, wraps around the neck of the fibula
• Pierces peroneus longus and divides into:
  • Superficial peroneal nerve
  • Deep peroneal nerve

Superficial Peroneal Nerve

• Passes between peroneus longus and brevis, becomes superficial
• Crosses extensor retinaculum to the dorsum of the foot

Deep Peroneal Nerve

• Pierces anterior fascial septum, enters anterior compartment
• Descends deep to extensor digitorum longus
• Accompanies anterior tibial artery, enters foot deep to extensor retinacula

Innervations

Before division:

• Peroneal communicating nerve → joins medial sural cutaneous → sural nerve
• Lateral sural cutaneous nerve → skin of lateral leg
• Nerve to short head of biceps
• Articular branch to knee joint

Superficial Peroneal Nerve:

• Motor: Peroneus longus, Peroneus brevis
• Sensory: Dorsum/lateral foot, lateral 3½ toes

Deep Peroneal Nerve:

• Motor:
  • Tibialis anterior
  • Extensor digitorum longus
  • Peroneus tertius
  • Extensor hallucis longus
  • Extensor digitorum brevis
• Sensory: Adjacent sides of first and second toes, branch to ankle joint

Pathology

Causes of Common Peroneal Nerve Lesions

1. Trauma:
   • Especially at fibular neck
   • Risk with tight plaster casts
2. Neuropraxia:
   • Compartment syndrome of lateral compartment
3. Mass lesions:
   • Tumours
   • Abscesses
4. Neuropathies:
   • Diabetes mellitus (ischemia)
   • Malignancy (compression/paraneoplastic)
   • Infective: Leprosy, HIV
   • CTDs: RA, SLE, PAN, scleroderma, sarcoidosis
   • Rare: Amyloidosis, Lyme disease, heavy metal poisoning

Clinical Assessment

Common finding is foot drop with weak eversion. Sensory loss may affect the dorsum of the foot and lateral leg depending on lesion location and severity.

Investigations

Blood tests (based on clinical suspicion):

• FBC
• U&Es / Glucose
• CRP
• ESR
• Additional tests as indicated

Imaging:

• CT or MRI to evaluate mass lesions or assess nerve integrity

Management

1. Treat underlying cause
2. Neuropraxias:
   • Fasciotomy if due to compartment syndrome
   • Remove tight casts
3. Occupational therapy:
   • Assist with splinting, adaptive supports
4. Physiotherapy:
   • Promote recovery, prevent contractures or deformity

Disposition

Dependent on:

• Onset
• Cause
• Severity

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Appendix 1

Common Peroneal Nerve Anatomy

Structures passing superficial to the extensor retinaculum of the ankle:

• Medially: Saphenous Nerve, Great Saphenous Vein.
• Laterally: Branches of the Superficial Peroneal Nerve.

Structures passing deep or through the extensor retinaculum of the ankle, (medial → lateral):

• Tibialis anterior.
• Extensor hallucis longus
• Anterior tibial artery (and its venae commitantes).
• Deep peroneal nerve
• Extensor digitorum longus (four tendons)
• Peroneus tertius.

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Appendix 2

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References

Publications

• Brazis PW, Masdeu JC, Biller J. Localization in Clinical Neurology. 8e 2021
• Fuller G. Neurological Examination Made Easy. 6e 2019
• O’Brien M. Aids to the Examination of the Peripheral Nervous System. 6e 2023

FOAMed

• Coni R. Neuro 101: Peripheral Nervous System. LITFL
• Nickson C. Myotomes and Differentiating Nerve Lesions. LITFL