Editing Sciatica (section)

==Pathophysiology==
The sciatic nerve comprises nerve roots L4, L5, S1, S2, and S3 in the spine.<ref>Giuffre BA, Black AC, Jeanmonod R. [https://www.ncbi.nlm.nih.gov/books/NBK482431/ Anatomy, Sciatic Nerve]. [Updated 2023 May 4]. In: StatPearls [Internet]. Treasure Island (Florida): StatPearls Publishing; 2023 January. Available from: https://www.ncbi.nlm.nih.gov/books/NBK482431/.</ref> These nerve roots merge in the pelvic cavity to form the [[sacral plexus]] and the sciatic nerve branches from that. Sciatica symptoms can occur when there is pathology anywhere along the course of these nerves.<ref name=":02">Davis D, Maini K, Vasudevan A. [https://www.ncbi.nlm.nih.gov/books/NBK507908/ Sciatica]. [Updated 2022 May 6]. In: StatPearls [Internet]. Treasure Island (Florida): StatPearls Publishing; 2023 January. Available from: https://www.ncbi.nlm.nih.gov/books/NBK507908/.</ref>

=== Intraspinal sciatica ===
[[File:728 Herniated Disk.jpg|thumb|348x348px|Left: Illustration of herniated spinal disc, superior view. Right: MRI showing herniated L5-S1 disc (red arrow tip), sagittal view.]]
Intraspinal, or discogenic sciatica refers to sciatica whose pathology involves the spine. In 90% of sciatica cases, this can occur as a result of a spinal disc bulge or [[spinal disc herniation|herniation]].<ref name=":3" /><ref>{{cite journal |vauthors=((Siddiq MAB)), Clegg D, Hasan SA, Rasker JJ |date=October 2020 |title=Extra-spinal sciatica and sciatica mimics: a scoping review |url= |journal=Korean J Pain |volume=33 |issue=4 |pages=305–317 |doi=10.3344/kjp.2020.33.4.305 |pmc=7532296 |pmid=32989195}}</ref> Sciatica is generally caused by the compression of [[lumbar nerves]] L4 or L5 or [[sacral nerves|sacral nerve]] S1.<ref name=":4">{{Cite book|title=Practical Office Orthopedics|last=Parks|first=Edward|publisher=McGraw-Hill|year=2017|isbn=9781259642876|location=[New York, N.Y.]|pages=Chapter 6: Low Back Pain|oclc=986993775}}</ref> Less commonly, [[sacral nerves]] S2 or S3 may cause sciatica.<ref name=":4" />

Intervertebral spinal discs consist of an outer [[Anulus fibrosus disci intervertebralis|anulus fibrosus]] and an inner [[Intervertebral disc|nucleus pulposus]].<ref name=":3" /> The [[Anulus fibrosus disci intervertebralis|anulus fibrosus]] forms a rigid ring around the [[Intervertebral disc|nucleus pulposus]] early in human development, and the gelatinous contents of the nucleus pulposus are thus contained within the disc.<ref name=":3" /> Discs separate the spinal vertebrae, thereby increasing spinal stability and allowing nerve roots to properly exit through the spaces between the vertebrae from the spinal cord.<ref>{{Cite book|url=https://accessmedicine.mhmedical.com/book.aspx?bookID=980|title=Schwartz's Principles of Surgery|last=Halpern|first=Casey H.|publisher=McGraw-Hill|others=Grady, M. Sean|year=2015|isbn=9780071800921|edition=   Tenth |location=[New York]|pages=Chapter 42: Neurosurgery|oclc=892490454}}</ref> As an individual ages, the [[Anulus fibrosus disci intervertebralis|anulus fibrosus]] weakens and becomes less rigid, making it at greater risk for tear.<ref name=":3" /> When there is a tear in the [[Anulus fibrosus disci intervertebralis|anulus fibrosus]], the [[Intervertebral disc|nucleus pulposus]] may extrude through the tear and press against spinal nerves within the spinal cord, [[cauda equina]], or exiting [[nerve root]]s, causing inflammation, numbness, or excruciating pain.<ref name=":1">{{Cite book |editor-last=LeBlond |editor-first=Richard F. |editor2-last=Brown |editor2-first=Donald D. |editor3-last=Suneja |editor3-first=Manish |editor4-last=Szot |editor4-first=Joseph F. |year=2015 |chapter=Chapter 13: The Spine, Pelvis, and Extremities |title=DeGowin's Diagnostic Examination |url=https://accessmedicine.mhmedical.com/book.aspx?bookid=1192 |edition=Tenth |location=New York |publisher=McGraw-Hill Education |isbn=9780071814478 |oclc=876336892}}</ref> Inflammation of spinal tissue can then spread to adjacent facet joints and cause [[facet syndrome]], which is characterized by lower back pain and referred pain in the [[Posterior compartment of thigh|posterior thigh]].<ref name=":3" />

Other causes of sciatica secondary to spinal nerve entrapment include the roughening, enlarging, or misalignment (''[[spondylolisthesis]]'') of [[vertebra]]e, or [[degenerative disc disease|disc degeneration]] that reduces the diameter of the lateral foramen through which nerve roots exit the spine.<ref name=":3" /> When sciatica is caused by compression of a [[dorsal nerve root]], it is considered a lumbar [[radiculopathy]] or [[radiculitis]] when accompanied by an inflammatory response.<ref name=":2" />

=== Extraspinal sciatica ===
[[File:Fibrovascular entrapment of the sciatic nerve undefined distribution.jpg|thumb|Illustration of fibrovascular bands restricting mobility of the sciatic nerve in multiple directions, like a splattering of glue]]
The sciatic nerve is highly mobile during hip and leg movements.<ref>{{cite journal |vauthors=Martin HD, Khoury AN, Schroder R, Gomez-Hoyos J, Yeramaneni S, Reddy M, James Palmer I |date=July 2017 |title=The effects of hip abduction on sciatic nerve biomechanics during terminal hip flexion |url= |journal=J Hip Preserv Surg |volume=4 |issue=2 |pages=178–186 |doi=10.1093/jhps/hnx008 |pmc=5467418 |pmid=28630740}}</ref><ref>{{cite journal |vauthors=Alshami AM, Alshammari TK, AlMuhaish MI, Hegazi TM, Tamal M, Abdulla FA |date=June 2022 |title=Sciatic nerve excursion during neural mobilization with ankle movement using dynamic ultrasound imaging: a cross-sectional study |url= |journal=J Ultrasound |volume=25 |issue=2 |pages=241–249 |doi=10.1007/s40477-021-00595-7 |pmc=9148322 |pmid=34036554}}</ref> Any pathology which restricts normal movement of the sciatic nerve can put abnormal pressure, strain, or tension on the nerve in certain positions or during normal movements. For example, the presence of [[Scar|scar tissue]] around a nerve can cause traction neuropathy.<ref>{{cite journal |vauthors=Crosio A, Ronchi G, Fornasari BE, Odella S, Raimondo S, Tos P |date=April 2021 |title=Experimental Methods to Simulate and Evaluate Postsurgical Peripheral Nerve Scarring |url= |journal=J Clin Med |volume=10 |issue=8 |page=1613 |doi=10.3390/jcm10081613 |pmc=8070420 |pmid=33920209 |doi-access=free }}</ref>

A well known muscular cause of extraspinal sciatica is [[piriformis syndrome]]. The [[piriformis muscle]] is directly adjacent to the course of the sciatic nerve as it traverses through the intrapelvic space. Pathologies of the piriformis muscle such as injury (e.g. swelling and scarring), inflammation (release of [[cytokine]]s affecting the local cellular environment), or space occupying lesions (e.g. tumor, cyst, hypertrophy) can affect the sciatic nerve.<ref name=":02"/> Anatomic variations in nerve branching can also predispose the sciatic nerve to further compression by the piriformis muscle, such as if the sciatic nerve pierces the piriformis muscle.<ref>{{cite journal |vauthors=ROBINSON DR |date=March 1947 |title=Pyriformis syndrome in relation to sciatic pain |url= |journal=Am J Surg |volume=73 |issue=3 |pages=355–358 |doi=10.1016/0002-9610(47)90345-0 |pmid=20289074}}</ref>

The sciatic nerve can also be entrapped outside of the pelvic space and this is called [[deep gluteal syndrome]].<ref name=":5">{{cite journal |vauthors=Kizaki K, Uchida S, Shanmugaraj A, Aquino CC, Duong A, Simunovic N, Martin HD, Ayeni OR |date=October 2020 |title=Deep gluteal syndrome is defined as a non-discogenic sciatic nerve disorder with entrapment in the deep gluteal space: a systematic review |url= |journal=Knee Surg Sports Traumatol Arthrosc |volume=28 |issue=10 |pages=3354–3364 |doi=10.1007/s00167-020-05966-x |pmid=32246173|s2cid=214784014 }}</ref> Surgical research has identified new causes of entrapment such as fibrovascular scar bands, vascular abnormalities, [[Heterotopic ossification|heterotropic ossification]], [[gluteal muscles]], [[Hamstring|hamstring muscles]], and the [[Gemelli muscles|gemelli]]-[[Obturator internus muscle|obturator internus]] complex.<ref name=":6">{{cite journal |vauthors=Martin HD, Reddy M, Gómez-Hoyos J |date=July 2015 |title=Deep gluteal syndrome |url= |journal=J Hip Preserv Surg |volume=2 |issue=2 |pages=99–107 |doi=10.1093/jhps/hnv029 |pmc=4718497 |pmid=27011826}}</ref> In almost half of the endoscopic surgery cases, fibrovascular scar bands were found to be the cause of entrapment, impeding the movement of the sciatic nerve.<ref>{{cite journal |vauthors=Martin HD, Shears SA, Johnson JC, Smathers AM, Palmer IJ |date=February 2011 |title=The endoscopic treatment of sciatic nerve entrapment/deep gluteal syndrome |url= |journal=Arthroscopy |volume=27 |issue=2 |pages=172–81 |doi=10.1016/j.arthro.2010.07.008 |pmid=21071168|doi-access=free }}</ref><ref>{{cite journal |vauthors=Park MS, Yoon SJ, Jung SY, Kim SH |date=May 2016 |title=Clinical results of endoscopic sciatic nerve decompression for deep gluteal syndrome: mean 2-year follow-up |url= |journal=BMC Musculoskelet Disord |volume=17 |issue= |pages=218 |doi=10.1186/s12891-016-1062-3 |pmc=4875686 |pmid=27206482 |doi-access=free }}</ref>