The sural nerve is a peripheral nerve located in the lower extremity, responsible for supplying sensation to the skin of the lower leg and foot. It is categorized as a purely sensory nerve, meaning its function is to carry feeling information back to the central nervous system, not to control muscle movement. Understanding the nerve’s precise location is important because its superficial course makes it particularly vulnerable to injury from trauma, compression, and surgical procedures.
The Anatomical Journey
The sural nerve is typically formed by the junction of two distinct branches in the calf. Its main contributor is the medial sural cutaneous nerve, which branches off the larger tibial nerve higher up in the leg. This nerve is joined by the lateral sural cutaneous nerve, a branch originating from the common fibular nerve. This union usually occurs in the distal third of the calf, though the exact point of fusion can vary significantly between individuals.
Once formed, the nerve descends through the posterior compartment of the lower leg, traveling in the subcutaneous fat layer. A defining characteristic of its path is its close relationship with the small saphenous vein, running alongside the vein as it courses toward the ankle. This superficial position makes the nerve easily accessible, but also prone to external pressure or damage.
The nerve continues its descent, passing just behind the lateral malleolus, the prominent bony bump on the outside of the ankle. It then enters the foot, where it gives off smaller branches, including the lateral calcaneal branches that supply the heel. The main trunk of the nerve terminates as the lateral dorsal cutaneous nerve, which runs along the outer border of the foot toward the fifth toe.
Sensory Role in the Lower Leg and Foot
The sural nerve provides cutaneous sensation, relaying information about touch, pain, and temperature from the skin. It does not control any muscles in the leg or foot.
The area of skin innervated by the nerve includes the posterolateral aspect of the lower leg, specifically the distal third of the calf. It provides sensation to the skin over the lateral ankle and the heel via its lateral calcaneal branches. The nerve is also responsible for feeling along the lateral border of the foot, extending to the fifth toe.
Common Injuries and Nerve Entrapment
Sural Nerve Entrapment
The superficial location of the sural nerve, particularly as it runs near the ankle and heel, makes it susceptible to sural nerve entrapment, or sural neuritis. This occurs when the nerve is compressed or irritated by surrounding structures. Common causes include trauma, such as an ankle sprain, which can cause swelling or scar tissue to press on the nerve.
Symptoms of entrapment typically manifest as neuropathic pain, which is described as burning, sharp, or shooting discomfort along the nerve’s distribution. Patients may also experience paresthesia, which includes tingling or a “pins and needles” sensation, and numbness in the lower leg and lateral foot. Repetitive activities like running, or external factors such as tight footwear or casts, can also aggravate or cause the compression.
Iatrogenic Injury and Grafting
The sural nerve is also highly vulnerable to iatrogenic injury, meaning damage caused unintentionally during medical procedures. Because of its location, it can be accidentally nicked or severed during common surgeries, including ankle fracture repair, Achilles tendon repair, or procedures involving the small saphenous vein. This can result in chronic pain or permanent numbness in its sensory field.
Due to its purely sensory nature and the relatively non-critical function of its sensation area, the sural nerve is frequently used in nerve grafting procedures. When a segment of a more important motor nerve is damaged, a portion of the sural nerve can be harvested to bridge the gap, providing a scaffold for the injured nerve to regenerate without causing major functional deficits.