The common fibular nerve, also known as the common peroneal nerve, is one of the two terminal branches of the sciatic nerve, the other being the tibial nerve. It is a mixed nerve, containing both motor and sensory fibers. The common fibular nerve is responsible for innervating muscles and skin in the lower leg and foot.
Location
The common fibular nerve originates from the sciatic nerve at the upper part of the popliteal fossa, located behind the knee. It courses laterally along the posterior aspect of the knee, curving around the neck of the fibula. At this point, it divides into its two terminal branches: the superficial fibular nerve and the deep fibular nerve. It is located superficially at the fibular neck, making it prone to injury.
Structure and Anatomy
The common fibular nerve, also known as the common peroneal nerve, is a major peripheral nerve of the lower limb. Below is a detailed description of its anatomical course, branches, and important anatomical relations.
Origin
The common fibular nerve originates as a terminal branch of the sciatic nerve in the popliteal fossa, just above the knee joint. The sciatic nerve bifurcates into the common fibular nerve and the tibial nerve, with the common fibular nerve taking the lateral course.
Course in the Popliteal Fossa
Proximal Leg (Popliteal Fossa)
The common fibular nerve begins in the upper portion of the popliteal fossa, a shallow depression located at the back of the knee. As it emerges from the sciatic nerve, it travels laterally and follows the border of the biceps femoris muscle (the long head) towards the fibula.
Lateral Course
It continues to descend toward the lateral aspect of the popliteal fossa, crossing obliquely behind the knee joint. As it approaches the lateral knee, it remains relatively superficial and wraps around the lateral side of the fibular head.
Relationship to Surrounding Structures
Muscles
- Biceps Femoris: The nerve runs along the lateral border of the biceps femoris muscle, which forms part of the hamstrings group, before wrapping around the fibular head.
- Gastrocnemius (Lateral Head): In the popliteal fossa, the common fibular nerve lies superficially to the lateral head of the gastrocnemius muscle, though it does not innervate this muscle.
Bone
Fibular Neck: One of the most important anatomical landmarks for the common fibular nerve is its close association with the neck of the fibula. The nerve winds around the fibular neck, lying just beneath the skin and superficial fascia, making it vulnerable to injury. It then moves forward from the posterior aspect of the leg to the lateral and anterior parts of the leg.
Branches
Before its bifurcation into terminal branches, the common fibular nerve gives off several smaller branches:
Lateral Sural Cutaneous Nerve
This sensory branch provides innervation to the skin over the upper lateral aspect of the leg. In some cases, it contributes to the formation of the sural nerve through communication with the medial sural cutaneous nerve (from the tibial nerve).
Articular Branches
The common fibular nerve sends articular branches to the knee joint, which provide sensory innervation to the capsule and ligaments of the knee.
Division into Terminal Branches
As the common fibular nerve winds around the fibular neck, it divides into its two terminal branches:
Superficial Fibular Nerve
The superficial fibular nerve descends into the lateral compartment of the leg, where it supplies the fibularis longus and fibularis brevis muscles. It also gives rise to sensory branches that innervate the skin on the dorsum of the foot, except for the web space between the first and second toes.
Deep Fibular Nerve
The deep fibular nerve enters the anterior compartment of the leg, running alongside the anterior tibial artery. It innervates the muscles responsible for dorsiflexion of the foot and the extension of the toes. The deep fibular nerve also provides sensory innervation to the web space between the first and second toes.
Anatomical Landmarks
- Popliteal Fossa: The nerve starts its course in the popliteal fossa, traveling along the lateral border of the biceps femoris.
- Fibular Head/Neck: The nerve wraps around the fibular neck before dividing into its terminal branches.
Variations in Anatomy
The path of the common fibular nerve is relatively consistent across individuals, though variations in its branching patterns may occur. The lateral sural cutaneous nerve, in particular, may form variable connections with other sensory branches, leading to differences in sural nerve formation.
Terminal Course
After dividing into the superficial and deep fibular nerves at the fibular neck, these branches continue to travel through their respective compartments (lateral and anterior) to supply the muscles and skin of the lower leg and foot.
Function
The common fibular nerve is a mixed nerve that provides both motor and sensory functions in the lower leg and foot. These functions are executed primarily through its terminal branches, the superficial fibular nerve and deep fibular nerve. Below is a detailed breakdown of its functions.
Motor Functions
The common fibular nerve itself does not directly innervate muscles; instead, its motor functions are carried out by its two major branches, the superficial fibular nerve and deep fibular nerve, which innervate muscles in the lateral and anterior compartments of the leg, respectively.
Motor Functions of the Superficial Fibular Nerve
The superficial fibular nerve innervates muscles in the lateral compartment of the leg. These muscles are responsible for foot eversion and help stabilize the ankle during movement:
- Fibularis Longus (Peroneus Longus): This muscle is responsible for everting the foot (turning the sole outward) and assisting in plantarflexion (pointing the toes downward). It also helps support the arch of the foot.
- Fibularis Brevis (Peroneus Brevis): This muscle assists in foot eversion and provides stability to the lateral aspect of the foot.
Motor Functions of the Deep Fibular Nerve
The deep fibular nerve innervates muscles in the anterior compartment of the leg, which are primarily responsible for dorsiflexion of the foot (lifting the foot upward) and extension of the toes:
- Tibialis Anterior: This is the primary dorsiflexor of the foot, lifting the foot toward the shin during walking and running.
- Extensor Hallucis Longus: This muscle extends the big toe and assists with dorsiflexion of the foot.
- Extensor Digitorum Longus: This muscle extends the lateral four toes and also contributes to dorsiflexion of the foot.
- Fibularis Tertius: This small muscle assists with both foot eversion and dorsiflexion.
In the foot, the deep fibular nerve also innervates the intrinsic muscles:
- Extensor Digitorum Brevis: This muscle extends the toes (second to fourth) and assists with fine motor control of the toes.
- Extensor Hallucis Brevis: This muscle helps extend the big toe.
Sensory Functions
The common fibular nerve provides sensory innervation via its branches, particularly through the lateral sural cutaneous nerve and terminal branches (superficial and deep fibular nerves).
Sensory Functions of the Lateral Sural Cutaneous Nerve
The lateral sural cutaneous nerve arises from the common fibular nerve and provides sensory innervation to the upper lateral part of the leg. It conveys sensations such as touch, temperature, and pain from the skin in this region.
Sensory Functions of the Superficial Fibular Nerve
The superficial fibular nerve supplies sensory innervation to the skin on the lower lateral leg and the dorsum of the foot, excluding the web space between the first and second toes. Sensations such as light touch, pain, temperature, and pressure are conveyed from the skin to the brain.
Sensory Functions of the Deep Fibular Nerve
The deep fibular nerve provides sensory innervation to a specific area of the foot: the web space between the first and second toes. This region, known as the first interdigital cleft, is the only area of skin that the deep fibular nerve innervates.
Reflexes and Coordination
Although the common fibular nerve’s role in reflexes is indirect (through its branches), it plays a part in maintaining balance and gait through motor control over muscles involved in dorsiflexion, eversion, and stabilization of the foot. Proper function of this nerve is critical for coordinated movement of the foot, especially during walking, running, and balancing on uneven surfaces.
Communication with Other Nerves
In some individuals, the lateral sural cutaneous nerve may communicate with the medial sural cutaneous nerve (a branch of the tibial nerve) to form the sural nerve. This communication allows for shared sensory input to the lower lateral leg and foot.
Clinical Significance
The common fibular nerve is clinically significant due to its susceptibility to injury, particularly because of its superficial position around the fibular neck. Injury to this nerve can lead to various motor and sensory deficits.
Foot Drop
Damage to the common fibular nerve, especially near the fibular neck, can cause foot drop. This condition is characterized by the inability to dorsiflex the foot, resulting in difficulty lifting the foot during walking. Patients with foot drop exhibit a “high-stepping” gait to compensate for the inability to clear the foot off the ground.
Nerve Compression
Compression of the common fibular nerve, such as from prolonged leg crossing, tight casts, or trauma, can lead to sensory loss and weakness in foot eversion and dorsiflexion. Common compression points include the fibular head and neck.
Trauma and Surgery
Because the common fibular nerve is superficial at the fibular neck, it is prone to injury during trauma, fractures of the fibula, or surgical procedures around the knee. Iatrogenic injury can occur during surgeries like knee arthroscopy or fibular osteotomies.
Sensory Deficits
Damage to the nerve can lead to numbness and tingling in the lateral leg and dorsum of the foot, particularly the web space between the first and second toes, due to disruption of sensory branches.
