The sural nerve ''(L4-S1)'' is generally considered a pure cutaneous nerve of the posterolateral leg to the lateral ankle. The sural nerve originates from a combination of either the sural communicating branch and

medial sural cutaneous nerve The medial sural cutaneous nerve ''(L4-S3)'' is a sensory nerve of the leg. It supplies cutaneous innervation the posteromedial leg. Structure The medial sural cutaneous nerve originates from the posterior aspect of the tibial nerve of the ...

, or the

lateral sural cutaneous nerve The lateral sural cutaneous nerve of the lumbosacral plexus supplies the skin on the posterior and lateral surfaces of the leg. The lateral sural cutaneous nerve originates from the common fibular nerve''(L4-S2)'' and is the terminal branch o ...

. This group of nerves is termed the sural nerve complex. There are eight documented variations of the sural nerve complex. Once formed the sural nerve takes its course midline posterior to posterolateral around the lateral malleolus. The sural nerve terminates as the lateral dorsal cutaneous nerve.

Anatomy

The sural nerve ''(L4-S1)'' is a

cutaneous Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different d ...

sensory

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the e ...

of the posterolateral

calf Calf most often refers to: * Calf (animal), the young of domestic cattle. * Calf (leg), in humans (and other primates), the back portion of the lower leg Calf or calves may also refer to: Biology and animal byproducts * Veal, meat from calves * ...

with

innervation A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the e ...

to the distal one-third of the lower leg. Formation of the ''sural nerve'' is the result of either

anastomosis An anastomosis (, plural anastomoses) is a connection or opening between two things (especially cavities or passages) that are normally diverging or branching, such as between blood vessels, leaf#Veins, leaf veins, or streams. Such a connection m ...

of the

and the sural communicating nerve, or it may be found as a continuation of the

traveling parallel to the medial sural cutaneous nerve. The ''sural nerve'' specifically innervates

sensorium A sensorium (/sɛnˈsɔːrɪəm/) (plural: sensoria) is the apparatus of an organism's perception considered as a whole, the "seat of sensation" where it experiences, perceives and interprets the environments within which it lives. The term origi ...

over the posterolateral leg and lower lateral ankle via lateral calcaneal branches.

Innervation

The sural nerve provides

to the

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod exoskeleton, have diffe ...

of the posterior to posterolateral

leg A leg is a weight-bearing and locomotive anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single, linear element ca ...

. This

is part of the sciatic nerve

. It only provides autonomic and sensory nerve fibers to the skin of the posterolateral leg and ankle. These fibers originate from

perikaryon The soma (pl. ''somata'' or ''somas''), perikaryon (pl. ''perikarya''), neurocyton, or cell body is the bulbous, non-process portion of a neuron or other brain cell type, containing the cell nucleus. The word 'soma' comes from the Greek '' σῶ� ...

located in the

spinal ganglia A dorsal root ganglion (or spinal ganglion; also known as a posterior root ganglion) is a cluster of neurons (a ganglion) in a dorsal root of a spinal nerve. The cell bodies of sensory neurons known as first-order neurons are located in the dorsal ...

and travel via the

lumbosacral plexus The anterior divisions of the lumbar nerves, sacral nerve A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on ...

via

nerve roots A nerve root (Latin: ''radix nervi'') is the initial segment of a nerve leaving the central nervous system. Nerve roots can be classified as: *Cranial nerve roots: the initial or proximal segment of one of the twelve pairs of cranial nerves leaving ...

L4-S1. When testing for deficits understand that often multiple nerves (lateral calcaneal nerve, sural nerve, and lateral dorsal cutaneous nerves of the foot) provide a complicated marriage of converging sensorium around the lower extremity.

Anatomic Course

Grossly, the course of this nerve leads it from it
highly varied anastomotic formation
to its more predictable terminal course down the remaining posterior leg. The anastomosis forming the sural nerve typically occurs in the deep fascia above or within the surrounding space above the gastrocnemius muscle. Once formed, the sural nerve then pierces out of a fascial crura and travels from its posterior midline position wrapping laterally around the lateral malleolus; once around the lateral malleolus the name of the nerve changes to the lateral dorsal cutaneous nerve. Eight variations of sural nerve origin have been described with categorical subtyping.

Anatomic Formation

The nerves contributing to the formation of the sural nerve ''(

, sural communicating nerve)'' are deemed the '' sural nerve complex'' by some anatomists and surgeons. Eight formations of the '' sural nerve complex'' have been described in cadaveric studies.

Morphometrics

The pathway of the sural nerve ''(once formed)'' is consistent as it travels superficially in the posterior leg over the distal part of the gastrocnemius over the beginning of the

achilles tendon The Achilles tendon or heel cord, also known as the calcaneal tendon, is a tendon at the back of the lower leg, and is the thickest in the human body. It serves to attach the plantaris, gastrocnemius (calf) and soleus muscles to the calcaneus (h ...

and then travels parallel to the achilles with the

small saphenous vein The small saphenous vein (also short saphenous vein or lesser saphenous vein) is a relatively large superficial vein of the posterior leg. Structure The origin of the small saphenous vein, (SSV) is where the dorsal vein from the fifth digit (small ...

to send of lateral calcaneal branches while the remaining nerve passes under the

lateral malleolus A malleolus is the bony prominence on each side of the human ankle. Each leg is supported by two bones, the tibia on the inner side (medial) of the leg and the fibula on the outer side (lateral) of the leg. The medial malleolus is the promine ...

and finally finding its ''terminal name'' as the sural nerve becomes the

lateral dorsal cutaneous nerve The lateral dorsal cutaneous nerve is a cutaneous branch of the foot. This nerve is the terminal nerve portion of the sural nerve. The common convention for where the sural nerve transitions into the ''lateral dorsal cutaneous nerve'' is after th ...

. The formation patterns of the sural nerve complex is much more complicated and highly varied as documented by anatomists. The ''most common formation'' is the anastomotic scenario described above; the sural communicating branch joins the medial sural cutaneous nerve to become the sural nerve. Type 1 and 2 sural nerve complex formation prevalence is estimated up to greater than 70%, Although the remaining types (3-8) provide difficulty in making consistent clinical approximation of this nerve in the random population. The sural nerve then travels out of deep fascia to the subcutaneous posterior sura. Although, these types of sural nerve complex (type 1 and 2) are of the highest prevalence there are multiple scenarios which other contributing nerves that range in morphology of formation, sural nerve size, and location of the sural nerve union. Anatomists limit the name of the sural nerve from its origins after an anastomosis of the SCB (type 1) and medial sural cutaneous nerve or we name it for when it penetrates out of the deep fascia of the posterior sura.

Clinical significance

The sural nerve has a purely sensory function, and so its removal results in only a relatively minor consequential deficit. Due to its large size and significant length it has had a significant contribution in medicine twofold; the sural nerve is the most frequently accessed donor nerve site for peripheral nerve grafting and serves as the primary diagnostic site for nerve conduction studies for understanding of peripheral nerve pathologies. It is frequently a site of iatrogenic nerve injury during percutaneous repair of the Achilles tendon or surgical interventions on the lower extremity. The sural nerve is also a source for iatrogenic injuries during orthopedic interventions of the lower ankle and extremity. For this reason, and due to its large size and significant length it has had a significant contribution in medicine in the form of

nerve biopsy In medicine, a nerve biopsy is an invasive procedure in which a piece of nerve is removed from an organism and examined under a microscope. A nerve biopsy can lead to the discovery of various necrotizing vasculitis, amyloidosis, sarcoidosis, lepro ...

and diagnostics of peripheral nerve diseases. Sural

mononeuropathy Peripheral neuropathy, often shortened to neuropathy, is a general term describing disease affecting the peripheral nerves, meaning nerves beyond the brain and spinal cord. Damage to peripheral nerves may impair sensation, movement, gland, or o ...

is uncommon, however If affected, it can be due to diabetes, peripheral neuropathies, or trauma. Sometimes inflammatory or vasculitic diseases will selectively involve the sural nerve. In addition, the sural nerve will be involved in any kind of generalized peripheral sensory or sensorimotor neuropathy. Sensory changes from sural neuropathy are variable but usually occur in the posterolateral aspect of the leg and the dorsolateral foot. These can sometimes be painful with

paresthesia Paresthesia is an abnormal sensation of the skin (tingling, pricking, chilling, burning, numbness) with no apparent physical cause. Paresthesia may be transient or chronic, and may have any of dozens of possible underlying causes. Paresthesias ar ...

s and

dysesthesia Dysesthesia is an unpleasant, abnormal sense of touch. Its etymology comes from the Greek word "dys," meaning "bad," and "aesthesis," which means "sensation" (abnormal sensation). It often presents as pain Joseph J. Marbach, Joseph Marbach hypo ...

Nerve conduction studies A nerve conduction study (NCS) is a medical diagnostic test commonly used to evaluate the function, especially the ability of electrical conduction, of the motor and sensory nerves of the human body. These tests may be performed by medical spec ...

can be used to delineate sural nerve lesions. Treatment will depend on the cause of the neuropathy. Occasionally biopsy of the nerve is performed for diagnostic purposes. For example, ganglions are usually resected. Traumatic neuropathy is usually treated non-surgically. It is often the donor nerve when a nerve allograft is performed.

Sural nerve block

A sural

nerve block Nerve block or regional nerve blockade is any deliberate interruption of signals traveling along a nerve, often for the purpose of pain relief. Local anesthetic nerve block (sometimes referred to as simply "nerve block") is a short-term block, ...

can be used for quick anesthetization to the foot and lower leg. Because this technique requires few injections to reach adequate

anesthesia Anesthesia is a state of controlled, temporary loss of sensation or awareness that is induced for medical or veterinary purposes. It may include some or all of analgesia (relief from or prevention of pain), paralysis (muscle relaxation), ...

, a smaller volume of anesthetic is needed. The sural nerve is rather superficial, which makes it more accessible to surgeons. Therefore, it is relatively easier than other procedures. Also, due to its superficial properties, the sural nerve is easily blocked at multiple levels at or above the ankle. In one study, regional anesthesia of the foot and ankle, when performed by surgeons, was completely successful 95% of the time. Sural nerve block is not advised if a patient is allergic to the anesthetic solution, has infected tissue at the injection site, has severe bleeding disorder, or has preexisting neurological damage.

Additional images

File:RobertSteele SuralNerve GraysMODified.png , Dissection of popliteal space to show the formation of a type 1 sural nerve File:sural nerve formation.jpg , Cartoon version adapted from Steele et al. depicting type 1 sural nerve File:Type 1-8 SN formation.jpg, 8 documented types of sural nerve formation File:Gray826and831.PNG, Areas of skin sensation supplied by nerves in the leg. File:Gray834.svg, Areas of skin supplied by nerves of the leg - the sural nerve supplies the lateral ankle. File:Gray835.png, Deep nerves of the front of the leg. File:Gray836.png, Course of nerves at the bottom of the foot.

References

External links

Referenced papers:
Steele et al. 208 sample cadaveric review 2021

Ramakrishnan et al.systematic review on sural nerve formation 2015
h2>

Anatomy web references

* *

{{Authority control Nerves of the lower limb and lower torso