The sural nerve is a sensory nerve located in the lower leg, providing feeling to the outer portion of the ankle and foot. As a purely sensory structure, it transmits touch, temperature, and pain signals from the skin without controlling muscle movement. Due to its superficial location and consistent size, the sural nerve is frequently involved in clinical procedures, making it a nerve of significant surgical and diagnostic interest. Understanding its anatomy and potential issues is useful for anyone experiencing lower leg or foot pain.
Anatomical Origin and Pathway
The sural nerve forms from contributions from two larger nerves: the tibial nerve and the common fibular nerve. The medial sural cutaneous nerve, a branch of the tibial nerve, descends through the calf between the two heads of the gastrocnemius muscle. The lateral sural cutaneous nerve branches from the common fibular nerve and travels over the lateral head of the same muscle.
These two nerves typically merge in the distal third of the posterior calf to form the sural nerve, though the exact point of union varies. Once formed, the nerve runs superficially down the back of the leg alongside the small saphenous vein, an anatomical relationship that is important clinically.
The nerve continues toward the ankle, passing just behind the lateral malleolus. It usually runs about 2.5 centimeters posterior to this bony prominence before extending along the lateral side of the foot. The sural nerve terminates as the lateral dorsal cutaneous nerve, providing sensation to the small toe.
Primary Function and Sensory Coverage
The sural nerve is a cutaneous nerve dedicated entirely to sensation, having no motor control over muscles. Its primary role is to relay information about external stimuli, such as pain, temperature, and vibration, back to the central nervous system. It also contributes to the sense of foot position, aiding in balance while standing and walking.
The area of skin innervated by this nerve is specific and predictable, covering the lower posterior third of the lateral calf. It provides sensory input to the skin over the lateral ankle and the heel. Its terminal branch extends this coverage to the lateral side of the foot and the fifth toe.
The sural nerve provides a reliable sensory map of the lower limb. Damage to the nerve or a successful nerve block procedure results in a sensory deficit, or numbness, corresponding precisely to this defined region. Its purely sensory nature is a factor in its frequent use in various medical procedures.
Common Clinical Issues and Injuries
The superficial course of the sural nerve makes it vulnerable to injury from trauma, compression, and surgical damage around the ankle and lower leg. A common issue is nerve entrapment, where the nerve becomes compressed or irritated by surrounding structures. This often occurs near the ankle following trauma, or where the nerve pierces the deep fascia of the calf (the superficial sural aponeurosis).
Entrapment causes symptoms like burning pain, tingling, or numbness (hyperesthesia or paresthesia) in the region the nerve supplies. Ankle sprains are a frequent cause of injury, as severe stretching of ligaments places excessive tension on the nerve, leading to pain or chronic discomfort. The nerve’s proximity to the small saphenous vein also makes it susceptible to accidental damage during vein harvesting procedures for coronary artery bypass surgery.
The sural nerve is the most common source for autologous nerve grafts, which are sections of nerve tissue used to repair damaged nerves elsewhere. It is chosen because it is purely sensory, has a good diameter, and provides a decent length of tissue. Removing the nerve results in a sensory deficit (numbness) in its distribution area, but this is generally well-tolerated since no motor function is affected.
The nerve is a frequent target for localized pain relief through nerve blocks. Healthcare providers inject an anesthetic near the nerve, often using ultrasound guidance, to temporarily numb its sensory field for surgical procedures or to diagnose chronic pain. The sural nerve is also a preferred site for a nerve biopsy, where a small section is removed for laboratory testing to help diagnose peripheral neuropathies.