Common fibular nerve

The common fibular nerve, also known as the common peroneal nerve, is a major branch of the sciatic nerve that plays a crucial role in lower limb motor and sensory function. Injury or compression of this nerve can lead to significant disability, including foot drop. Understanding its anatomy and function is essential for clinical assessment and management.

Anatomy

Origin

The common fibular nerve arises from the sciatic nerve, which contains contributions from spinal nerve roots L4 to S2. It separates from the tibial component of the sciatic nerve in the distal thigh and courses laterally around the knee.

Course

• After diverging from the sciatic nerve, the common fibular nerve passes laterally along the posterior aspect of the biceps femoris tendon.
• It wraps around the neck of the fibula, lying superficially just beneath the skin, making it susceptible to injury at this site.
• Distally, it divides into two terminal branches: the superficial fibular nerve and the deep fibular nerve, which continue to supply the lower leg and foot.

Branches

• Superficial fibular nerve: Provides motor innervation to the lateral compartment muscles and sensory supply to the lower lateral leg and dorsum of the foot.
• Deep fibular nerve: Supplies the anterior compartment muscles of the leg and sensory innervation to the web space between the first and second toes.
• Articular and cutaneous branches: Small branches contribute to knee joint innervation and cutaneous sensation over the lateral leg and upper foot.

Innervation

• Motor: Muscles of the anterior and lateral compartments of the leg, including tibialis anterior, extensor digitorum longus, fibularis longus, and fibularis brevis.
• Sensory: Skin over the anterolateral aspect of the leg, the dorsum of the foot, and the dorsal surfaces of toes.

Function

Motor Function

• Dorsiflexion of the foot at the ankle joint, allowing the toes to lift off the ground during gait.
• Eversion of the foot, enabling lateral movement of the sole for balance and walking on uneven surfaces.
• Extension of the toes, facilitating proper toe clearance during the swing phase of gait.

Sensory Function

• Sensation over the anterolateral portion of the lower leg, which includes the lateral shin and upper lateral calf.
• Sensation on the dorsum of the foot and toes, including the space between the first and second toes via the deep fibular nerve.

Clinical Significance

Common Injuries

The common fibular nerve is particularly vulnerable due to its superficial course around the fibular neck. Injuries can result from:

• Direct trauma to the lateral knee or proximal fibula
• Compression from casts, braces, or tight bandages
• Sports-related injuries involving twisting or forced inversion of the foot
• Prolonged leg crossing or habitual squatting in certain populations

Associated Conditions

• Foot drop: Inability to dorsiflex the foot due to weakness of anterior compartment muscles.
• Neuropathy: Diabetic or peripheral neuropathy can involve the common fibular nerve, causing sensory loss and weakness.
• Entrapment syndromes: Compression at the fibular neck may lead to pain, tingling, and muscle weakness in the affected distribution.

Clinical Examination

Inspection

• Observe for muscle atrophy in the anterior and lateral compartments of the leg.
• Assess gait for high-stepping or compensatory movements indicative of foot drop.
• Look for signs of trauma, swelling, or deformity around the fibular head.

Motor Testing

• Test dorsiflexion strength by asking the patient to lift the foot against resistance.
• Evaluate toe extension strength to assess deep fibular nerve function.
• Assess eversion strength to check superficial fibular nerve integrity.

Sensory Testing

• Check light touch and pinprick sensation over the anterolateral leg and dorsum of the foot.
• Perform two-point discrimination testing in areas supplied by the superficial and deep branches.
• Compare bilaterally to identify subtle deficits.

Diagnostic Investigations

Nerve Conduction Studies

Nerve conduction studies are used to evaluate the electrical conduction along the common fibular nerve. Reduced conduction velocity or prolonged latency can indicate demyelination or axonal injury.

Electromyography

Electromyography assesses the electrical activity of muscles innervated by the common fibular nerve. Findings may include signs of denervation, fibrillation potentials, or reinnervation changes, helping to localize the lesion and determine severity.

Imaging

• Ultrasound: Useful for detecting nerve entrapment, mass lesions, or neuromas along the course of the nerve.
• MRI: Provides high-resolution visualization of the nerve and surrounding soft tissues, assisting in surgical planning or identification of compression sites.

Management

Conservative Treatment

Initial management of common fibular nerve injuries often involves non-surgical approaches:

• Physical therapy focusing on strengthening affected muscles and maintaining joint mobility.
• Use of orthotic devices such as ankle-foot orthoses to prevent foot drop and facilitate walking.
• Pain management with medications and activity modification to prevent further nerve irritation.

Surgical Treatment

Surgery may be indicated in severe or persistent cases:

• Decompression procedures for entrapment at the fibular neck or due to scar tissue.
• Nerve repair or grafting in traumatic transection injuries.
• Tendon transfer procedures to restore dorsiflexion in patients with long-standing foot drop.

Prognosis

The prognosis of common fibular nerve injuries depends on the severity, cause, and promptness of treatment. Mild compression injuries often recover fully within weeks to months, while severe traumatic injuries may result in prolonged or incomplete recovery.

• Recovery timeline varies based on axonal damage; mild neuropraxia may resolve in 4–6 weeks, while axonotmesis may take several months.
• Early physiotherapy and use of orthotic devices improve functional outcomes and prevent secondary complications such as joint contractures.
• Persistent deficits may occur if the nerve injury is severe, prolonged, or untreated, potentially requiring surgical intervention or tendon transfers.

References

1. Standring S. Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. London: Elsevier; 2020.
2. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. 9th ed. Philadelphia: Wolters Kluwer; 2020.
3. Brushart TM. Nerve Repair. 2nd ed. New York: Oxford University Press; 2011.
4. O’Sullivan SB, Schmitz TJ. Physical Rehabilitation. 7th ed. Philadelphia: F.A. Davis; 2020.
5. Kim DH, Murovic JA, Tiel RL, Kline DG. Management and outcomes in 353 surgically treated lesions of the peroneal nerve. Neurosurgery. 2004;55(5):1121-1130.
6. Campbell WW. Evaluation and Management of Peripheral Nerve Injury. Clin Neurophysiol. 2008;119(9):1951-1965.
7. Riegler FM, Tubbs RS, Loukas M. Surgical Anatomy of the Common Fibular (Peroneal) Nerve. J Neurosurg. 2013;119(5):1100-1106.
8. de Medinaceli L. Entrapment of the Common Peroneal Nerve at the Fibular Head. Muscle Nerve. 1997;20(6):643-649.