Injury to the Common Fibular Nerve
The common fibular nerve and its branches are clinically significant due to their susceptibility to injury. Because the nerve wraps around the neck of the fibula, where it is relatively superficial, injuries involving this region are frequently encountered in clinical practice.
Vulnerability of the Common Fibular Nerve
The common fibular nerve is located deep to the fibularis longus muscle, following a precise course around the fibular neck. Due to its exposed position, it is particularly vulnerable to:
- Laceration from proximal fibular fractures
- Direct trauma or compression injuries
A critical concern arises when the deep branch of the common fibular nerve is injured, leading to complete loss of function in all dorsiflexor muscles located in the anterior compartment of the lower leg.
Effects of Deep Fibular Nerve Injury
Loss of dorsiflexor function results in the inability to control plantarflexion immediately after heel contact in gait.
Clinical Manifestations:
- Uncontrolled foot drop after heel strike, causing the foot to rapidly slap the ground.
- Compensatory gait adaptation in the swing phase, where the hip and knee excessively flex to prevent the toes from dragging.
- Increased risk of plantarflexion contractures due to prolonged dorsiflexor weakness.
This condition is clinically termed "foot drop" (pes equinus).
A key concern in foot drop is the rapid adaptive shortening of ligaments around the ankle, particularly the Achilles tendon and associated collateral ligaments. Gravity further accelerates this plantarflexion contracture, making normal gait progressively more difficult.
To maintain functional mobility, patients with foot drop typically require an ankle-foot orthosis (AFO) to support the foot in dorsiflexion and prevent excessive plantarflexion positioning.
Effects of Superficial Fibular Nerve Injury
If the superficial branch of the common fibular nerve is injured, paralysis occurs in the:
- Fibularis longus
- Fibularis brevis
Clinical Manifestations:
- Loss of eversion function
- Gradual development of supination (inversion) deformity, known as pes varus
In complete common fibular nerve injury, both the deep and superficial branches are affected, leading to combined dysfunction of dorsiflexion and eversion. This results in a characteristic foot deformity called pes equinovarus, where:
- The ankle is fixed in plantarflexion (equinus deformity)
- The foot remains in an inverted (supinated) position
This severe deformity significantly impairs gait mechanics, requiring surgical intervention or custom orthotic management to improve functional mobility.