The sural nerve (S1, S2) is a peripheral nerve that arises in the posterior compartment of the leg (calf or sural region). It is formed by the union of two smaller sensory nerves: the medial sural cutaneous nerve (a branch of the tibial nerve), and lateral sural cutaneous nerve (branch of the common fibular nerve). In the posterior leg, the sural nerve courses alongside the small saphenous vein.
The sural nerve is a purely sensory nerve. Its main function is to provide the sensory supply for the posterolateral aspect of the distal third of the leg, lateral aspect of the foot, heel and ankle.
This article will discuss the anatomy and function of the sural nerve.
|Medial sural cutaneous nerve, lateral sural cutaneous nerve
|Lateral dorsal cutaneous nerve of foot, lateral calcaneal branches of sural nerve
|Posterolateral aspect of the distal third of the leg, ankle, foot and heel
- Origin and course
- Branches and innervation
- Clinical relations
Origin and course
The sural nerve (S1, S2) originates in the posterior leg from a merger of two smaller nerves: the medial sural cutaneous nerve and the lateral sural cutaneous nerve. The medial sural cutaneous nerve branches from the tibial nerve (L4-S3) and descends in the posterior leg compartment between the two heads of the gastrocnemius muscle. The lateral sural cutaneous nerve is a branch of the common fibular (peroneal) nerve (L4-S2) that passes over the lateral head of the gastrocnemius muscle. Upon reaching the distal one-third of the leg, these nerves merge to form the sural nerve. However, it is important to note that the level of the union can vary greatly, from the popliteal fossa to the level of the ankle where the sural nerve enters the foot.
Upon arising, the sural nerve descends between the heads of the gastrocnemius muscle. It then passes near the lateral margin of the calcaneal tendon, ( running alongside the small saphenous vein until it reaches the ankle. The sural nerve then passes between the lateral malleolus and the calcaneus and enters into the foot. Upon reaching the lateral aspect of the foot, the nerve terminates as the lateral dorsal cutaneous nerve.
Branches and innervation
In the leg, the sural nerve directly innervates the skin over the posterolateral aspect of the distal third of the leg.
Upon entering the foot, the sural nerve gives off two terminal branches:
- Lateral calcaneal branch of sural nerve, which innervates the skin over the lateral portion of the heel.
- Lateral dorsal cutaneous nerve of foot, which supplies the lateral side of the dorsum of the foot. This nerve ends as a dorsal digital nerve for the sensory supply of the lateral aspect of the fifth toe.
The sural nerve entrapment
Sural nerve entrapment is a rare clinical condition that occurs when the nerve is compressed or fixed. One of the most common causes is fascial thickening which occurs when the rigid anatomic fibrous arcade formed at the fascial opening becomes thickened and doubled. This forms a fibrous arch that may compress the sural nerve. It can also be caused by fractures of the sural area, intrinsic factors (ganglions and lipomas), prolonged external compression, repetitive ankle sprains, and gastrocnemius muscle injury.
The diagnosis of sural entrapment neuropathy is based typically on physical examination. The symptoms usually include burning sural pain in the posterior aspect of the leg (often radiating pain in the distal foot), and abnormal nerve sensations (hypesthesia, dysaesthesia, or paraesthesia). The treatment depends on the etiology and the severity of the nerve damage. It usually includes conservative therapy (decompression method) or a surgical approach.
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