The sural nerve is a purely sensory nerve located in the lower leg and foot, dedicated to transmitting feelings from the skin to the central nervous system. Its name is derived from the Latin word “sura,” meaning calf. The nerve provides the brain with information about touch, temperature, pain, and vibration in a specific region of the lower limb. It is often discussed in medical contexts due to its clinical utility and susceptibility to injury.
Anatomy and Course
The sural nerve is formed by the joining of two smaller sensory nerves in the calf region. It is typically created from the medial sural cutaneous nerve, a branch of the tibial nerve, and the lateral sural cutaneous nerve, a branch of the common fibular (peroneal) nerve. This merger usually occurs in the distal third of the posterior leg.
Once formed, the nerve descends through the calf, lying just beneath the skin and superficial to the fascia. It courses alongside the small saphenous vein as it travels down the back of the leg. The nerve continues its path toward the ankle, passing about an inch posterior to the lateral malleolus (the outer ankle bone). It then extends onto the outer side of the foot, where it terminates as the lateral dorsal cutaneous nerve.
Sensory Role
The primary function of the sural nerve is to provide skin sensation to a distinct area of the lower limb. The nerve supplies sensation to the skin over the posterolateral aspect of the distal third of the leg, covering the back of the calf below the knee. Its innervation extends down to the foot, covering the outer side of the ankle and the heel, and the entire outer side of the foot, including the fifth toe. This sensory input is essential for detecting changes in temperature, pain, and touch, which contributes to maintaining balance by sensing foot position.
Injury and Neuropathy
The superficial location of the sural nerve makes it vulnerable to external trauma and compression, leading to sural neuropathy. Damage can range from direct impact, such as a sports injury, to prolonged external pressure from tight footwear or ankle braces. A common mechanism of injury is a severe lateral ankle sprain, where the nerve can be stretched or compressed as it passes around the ankle joint. Damage can also occur unintentionally during surgical procedures around the ankle or Achilles tendon, referred to as iatrogenic injury.
Symptoms of sural neuropathy are typically felt in the nerve’s distribution area and often include a lack of sensation or numbness. Patients frequently report tingling, burning, or electric shock-like pain, medically termed paresthesia. In some cases, light touch can cause significant pain, a condition called allodynia. Persistent pain or a painful lump, known as a neuroma, can develop at the site of a partial or complete nerve transection.
Medical Application
The sural nerve plays a unique role in medical procedures due to its purely sensory nature. Because its removal results in a sensory deficit limited to a small area of the lateral foot, it is the most frequently accessed donor nerve site in the body. Surgeons use sections of the sural nerve as autologous nerve grafts to repair more functionally significant nerve injuries elsewhere, such as the face, arm, or hand.
The nerve is also a preferred site for diagnostic nerve biopsies, a procedure used to help diagnose complex peripheral nerve disorders like vasculitis or various forms of peripheral neuropathy. Its superficial course and relatively large size make it easy to locate and harvest for both grafting and biopsy purposes. While harvesting the nerve causes a permanent loss of sensation, the resulting deficit is often considered a manageable trade-off for repairing a nerve with a major motor function.