The peroneal nerve is an important nerve in the lower leg, playing a role in both movement and sensation. It enables the ability to lift the foot and toes upward, known as dorsiflexion, and contributes to sensation in parts of the lower leg and foot.
Origin and General Path
The common peroneal nerve branches from the sciatic nerve, originating from spinal nerve roots in the lower back (L4-S2). It descends through the thigh, separating from the sciatic nerve near the popliteal fossa, the hollow area behind the knee. The nerve then courses inferolaterally, positioned medial to the biceps femoris muscle and lateral to the gastrocnemius muscle. It continues its descent towards the head of the fibula, the smaller bone in the lower leg, where it curves around the neck of this bone before dividing into its main branches.
Divisions and Specific Locations
After wrapping around the fibular neck, the common peroneal nerve divides into two branches: the superficial peroneal nerve and the deep peroneal nerve.
The superficial peroneal nerve travels down the lateral compartment of the leg, located between the fibularis longus and fibularis brevis muscles and the extensor digitorum longus muscle. This branch innervates the fibularis longus and brevis muscles, which are responsible for everting (turning outward) the foot and assisting with plantar flexion. It also provides sensation to the skin on the front and outer part of the lower leg and most of the top of the foot, excluding the area between the first and second toes.
The deep peroneal nerve enters the anterior compartment of the leg. It descends along the interosseous membrane, a fibrous sheet between the tibia and fibula. This nerve supplies the muscles in the anterior compartment, including the tibialis anterior, extensor digitorum longus, extensor hallucis longus, and fibularis tertius, which are important for dorsiflexing (lifting) the foot and extending the toes. The deep peroneal nerve also provides sensation to the skin area between the first and second toes.
Points of Vulnerability
The common peroneal nerve is susceptible to injury due to its superficial position as it winds around the fibular head, near the knee. At this location, it is covered by minimal tissue, making it vulnerable to external pressure and trauma. Common causes of injury include direct blows to the outer knee, fibula fractures, or prolonged pressure. Activities such as crossing the legs for extended periods, wearing tight casts on the lower leg, or sustained pressure during deep sleep can compress the nerve. Surgical procedures, particularly those involving the knee or hip, can also place the nerve at risk.
Recognizing Peroneal Nerve Impairment
Damage to the peroneal nerve often results in symptoms affecting movement and sensation. One common sign is “foot drop,” which describes difficulty or inability to lift the front part of the foot. This can lead to a “slapping” gait, where the foot slaps the ground while walking, or a person may lift their knee higher than usual to avoid dragging their toes. Weakness in lifting the ankle or toes upward (dorsiflexion) and difficulty turning the foot outward (eversion) are also common motor impairments.
Sensory symptoms include numbness, tingling, or a reduced ability to feel sensations in the outer part of the lower leg and the top of the foot. In some cases, prolonged nerve damage can lead to a decrease in muscle mass in the affected areas.