The sciatic nerve, also called the ischiadic nerve, is a large nerve in humans and other vertebrate animals. It is the largest branch of the sacral plexus and runs alongside the hip joint and down the right lower limb. It is the longest and widest single nerve in the human body, going from the top of the leg to the foot on the posterior aspect. The sciatic nerve has no cutaneous branches for the thigh. This nerve provides the connection to the nervous system for the skin of the lateral leg and the whole foot, the muscles of the back of the thigh, and those of the leg and foot. It is derived from Spinal nerve L4 to S3. It contains Axon from both the anterior and posterior divisions of the lumbosacral plexus.
Structure
In humans, the sciatic nerve is formed from the L4 to S3 segments of the sacral plexus, a collection of nerve fibres that emerge from the
Sacrum part of the
spinal cord. The lumbosacral trunk from the L4 and L5 roots descends between the sacral promontory and ala, and the S1 to S3 roots emerge from the ventral sacral foramina. These nerve roots unite to form a single nerve in front of the piriformis muscle. The nerve passes beneath the piriformis and through the greater sciatic foramen, exiting the pelvis.
From here, it travels down the posterior thigh to the
popliteal fossa. The nerve travels in the posterior compartment of the thigh behind (superficial to) the adductor magnus muscle and is itself in front of (deep to) the long head of the biceps femoris muscle. At the popliteal fossa, the nerve divides into its two branches:
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The tibial nerve, which travels down the posterior compartment of the leg into the foot
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The common fibular nerve (also called the common peroneal nerve), which travels down the anterior and lateral compartments of the leg into the foot
The sciatic nerve is the largest nerve in the human body.
Development
Function
The sciatic nerve supplies sensation to the
skin of the
foot, as well as the entire lower leg (except for its inner side). Sensation to skin to the sole of the foot is provided by the
tibial nerve, and the lower leg and upper surface of the foot via the common fibular nerve.
The sciatic nerve also innervates muscles. In particular:
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Via the tibial nerve, the muscles in the posterior compartment of the leg and sole of the foot (plantar aspect).
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Via the common fibular nerve, the muscles in the anterior and lateral compartments of the leg.
Clinical significance
Sciatica
Pain caused by compression or irritation of the sciatic nerve by a problem in the lower back is called
sciatica. Common causes of sciatica include the following lower back and hip conditions: spinal disc herniation, degenerative disc disease, lumbar spinal stenosis, spondylolisthesis, and piriformis syndrome.
Other acute causes of sciatica include
, muscular
hypertension, and
sneezing.
Injury
A sciatic nerve injury occurs between 0.5% and 2.0% of the time during a
Hip replacement replacement.
Sciatic nerve palsy is a complication of total hip arthroplasty with an incidence of 0.2% to 2.8% of the time, or with an incidence of 1.7% to 7.6% following revision.
Following the procedure, in rare cases, a screw, broken piece of trochanteric wire, fragment of methyl methacrylate bone cement, or Burch-Schneider antiprofusio cage can impinge on the nerve; this can cause sciatic nerve
palsy, which may resolve after the fragment is removed and the nerve is freed. The nerve can be surrounded by oxidised, regenerated cellulose to prevent further scarring. Sciatic nerve palsy can also result from severe
spinal stenosis following the procedure, which can be addressed by spinal decompression surgery.
[is cited by Stiehl and Stewart for the 0.5-2.0% figure.] It is unclear if inversion therapy is able to decompress the sacral vertebrae; it may only work on the lumbar aspects of the sciatic nerves.
A sciatic nerve injury may also occur from improperly performed injections into the buttock, and may result in sensory loss.
Other disease
Bernese periacetabular
osteotomy resulted in major nerve deficits in the sciatic or femoral nerves in 2.1% of 1760 patients, of whom approximately half experienced complete recovery within a mean of 5.5 months.
Sciatic nerve exploration can be done by endoscopy in a minimally invasive procedure to assess lesions of the nerve.
Anaesthetic
Signals from the sciatic nerve and its branches can be blocked, in order to interrupt the transmission of
Pain signal from the innervation area, by performing a regional nerve blockade called a sciatic nerve block.
Society and culture
According to
Jewish law, the sciatic nerve (
Hebrew:
Gid hanasheh) may not be eaten by Jews to commemorate
Jacob's injury in his struggle with an
angel.
==Additional images==
See also
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Lesser sciatic notch
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Greater sciatic notch
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Lumbosacral plexus
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Sacral plexus
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Tibial nerve
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Common peroneal nerve
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Peripheral nervous system
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Sciatica
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Spinal disc herniation
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Piriformis syndrome
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Deep gluteal syndrome
Notes
External links
