Editing Joint (section)

==Classification==

The number of joints depends on if [[Sesamoid bone|sesamoids]] are included, age of the human and the definition of joints. However, the number of sesamoids is the same in most people with variations being rare.<ref>{{Cite journal|last=Wood|first=V. E.|date=October 1984|title=The sesamoid bones of the hand and their pathology|url=https://pubmed.ncbi.nlm.nih.gov/6512360/#:~:text=Most%20people%20have%20five%20sesamoid,finger%20on%20the%20ulnar%20side.|journal=Journal of Hand Surgery (Edinburgh, Scotland)|volume=9|issue=3|pages=261–264|doi=10.1016/0266-7681(84)90038-x|issn=0266-7681|pmid=6512360|s2cid=72038079}}</ref><ref>{{Cite web|title=Sesamoid Injuries in the Foot – Sesamoiditis Foot {{!}} Foot Health Facts - Foot Health Facts|url=https://www.foothealthfacts.org/conditions/sesamoid-injuries-in-the-foot|access-date=2021-07-04|website=www.foothealthfacts.org}}</ref><ref>{{Cite journal|last1=Chen|first1=Wei|last2=Cheng|first2=Jiaxiang|last3=Sun|first3=Ran|last4=Zhang|first4=Zekun|last5=Zhu|first5=Yanbin|last6=Ipaktchi|first6=Kyros|last7=Zhang|first7=Yingze|date=2015-07-15|title=Prevalence and variation of sesamoid bones in the hand: a multi-center radiographic study|journal=International Journal of Clinical and Experimental Medicine|volume=8|issue=7|pages=11721–11726|issn=1940-5901|pmc=4565393|pmid=26380010}}</ref>

Joints are mainly classified structurally and functionally. Structural classification is determined by how the bones connect to each other, while functional classification is determined by the degree of movement between the articulating bones. In practice, there is significant overlap between the two types of classifications.

===Clinical, numerical classification===
*monoarticular – concerning one joint
*oligoarticular or pauciarticular – concerning 2–4 joints
*polyarticular – concerning 5 or more joints

=== Structural classification (binding tissue)===
[[File:Structural Classification of Joints.jpg|thumb|300x300px|Types of joints based upon their structure (L to R): cartilaginous joint, fibrous joint, and synovial joint.]]
Structural classification names and divides joints according to the type of binding tissue that connects the bones to each other.<ref name="Whiting2006p40"/> There are four structural classifications of joints:<ref name="umich2010ClByTiss">{{cite web |url=http://anatomy.med.umich.edu/modules/joints_module/joints_03.html 
|archive-url=https://web.archive.org/web/20110608081814/http://anatomy.med.umich.edu/modules/joints_module/joints_03.html |archive-date=2011-06-08 |title=Introduction to Joints (3) – Joints – Classification by Tissue Joining Bones |access-date=2008-01-29 | publisher=anatomy.med.umich.edu}}</ref>
* [[fibrous joint]] – joined by dense regular connective tissue that is rich in collagen fibers<ref name="anatomical">Principles of Anatomy & Physiology, 12th Edition, Tortora & Derrickson, Pub: Wiley & Sons</ref>
* [[cartilaginous joint]] – joined by [[cartilage]]. There are two types: [[Cartilaginous joint#Primary cartilaginous joints|primary cartilaginous joints]] composed of [[hyaline cartilage]], and [[Cartilaginous joint#Secondary cartilaginous joints|secondary cartilaginous joints]] composed of hyaline cartilage covering the articular surfaces of the involved bones with [[fibrocartilage]] connecting them.
* [[synovial joint]] – not directly joined – the bones have a synovial cavity and are united by the dense irregular connective tissue that forms the articular capsule that is normally associated with accessory ligaments.<ref name="anatomical"/>
* [[facet joint]] – joint between two articular [[process (anatomy)|processes]] between two vertebrae.<ref name="Medilexicon">{{cite web | url=http://www.medilexicon.com/medicaldictionary.php?t=31339 | publisher=Medilexicon – Medical Dictionary | title=Articular Facet | access-date=December 19, 2013 | archive-date=August 6, 2016 | archive-url=https://web.archive.org/web/20160806005701/http://www.medilexicon.com/medicaldictionary.php?t=31339 | url-status=dead }}</ref><ref>{{cite web | url=http://www.ontobee.org/browser/index.php?keywords=Articular+facet&Submit2=Search+terms&o=FMA | title=Foundational Model of Anatomy | access-date=December 19, 2013 | url-status=dead | archive-url=https://web.archive.org/web/20131219182622/http://www.ontobee.org/browser/index.php?keywords=Articular+facet&Submit2=Search+terms&o=FMA | archive-date=December 19, 2013 }}</ref>

===Functional classification (movement)===
Joints can also be classified functionally according to the type and degree of movement they allow:<ref name="Whiting2006p40"/><ref name="umich2010ClByMov">{{cite web |url=http://anatomy.med.umich.edu/modules/joints_module/joints_02.html |archive-url=https://web.archive.org/web/20110718163549/http://anatomy.med.umich.edu/modules/joints_module/joints_02.html |archive-date=2011-07-18 |title=Introduction to Joints (2) – Joints – Classification by Movement |access-date=2012-10-06 | publisher=anatomy.med.umich.edu}}</ref> Joint movements are described with reference to the basic [[anatomical planes]].<ref name="Saladinp274"/>
* [[synarthrosis]] – permits little or no mobility. Most synarthrosis joints are [[fibrous joint]]s, such as skull sutures. This lack of mobility is important, because the skull bones serve to protect the brain.<ref name="openstax">{{cite book|title=- Anatomy and Physiology|author=J. Gordon Betts |display-authors=et al|publisher=OpenStax|chapter=9.1 Classification of Joints|date=20 April 2022 |chapter-url=https://openstax.org/books/anatomy-and-physiology-2e/pages/9-1-classification-of-joints|access-date=13 May 2023|isbn=978-1-951693-42-8}}</ref>
* [[amphiarthrosis]] – permits slight mobility. Most amphiarthrosis joints are [[cartilaginous joint]]s. An example is the [[intervertebral disc]]. Individual intervertebral discs allow for small movements between adjacent vertebrae, but when added together, the vertebral column provides the flexibility that allows the body to twist, or bend to the front, back, or side.<ref name="openstax"/>
* [[synovial joint]] (also known as a ''diarthrosis'') – freely movable.<ref name="Whiting2006p40"/><ref name="umich2010ClByMov"/> Synovial joints can in turn be classified into six groups according to the type of movement they allow: [[plane joint]], [[ball and socket joint]], [[hinge joint]], [[pivot joint]],<ref name="Morton1849p119">{{cite book |author-link=Samuel George Morton |first1=Samuel George |last1=Morton |year=1849 |title=An Illustrated System of Human Anatomy |url=https://archive.org/details/61120330R.nlm.nih.gov/page/n128 |page=119}}</ref><ref name="Gray1859p136">{{cite book |author-link=Henry Gray |first=Henry |last=Gray |year=1859 |title=Anatomy, descriptive and surgical |url=https://archive.org/details/06220300R.nlm.nih.gov/page/n169 |page=136}}</ref> [[condyloid joint]] and [[saddle joint]].<ref name="Gray1887p220">{{cite book |author-link=Henry Gray |first=Henry |last=Gray |year=1887 |title=Anatomy, descriptive and surgical |url=https://archive.org/stream/anatodescripti00grayrich#page/220/mode/2up |page=220}}</ref>
Joints can also be classified, according to the number of axes of movement they allow, into nonaxial (gliding, as between the proximal ends of the ulna and radius), monoaxial (uniaxial), biaxial and [[Multiaxial joint|multiaxial]].<ref name="Platzer2008p28">{{cite book |last1=Platzer |first1=Werner |year=2008 |title=Color Atlas of Human Anatomy |volume=1 |url=https://books.google.com/books?id=T9bb4T422j8C&pg=PA28 |page=28|publisher=Thieme |isbn=9783135333069 }}</ref> Another classification is according to the [[Degrees of freedom (mechanics)|degrees of freedom]] allowed, and distinguished between joints with one, two or three degrees of freedom.<ref name="Platzer2008p28"/> A further classification is according to the number and shapes of the articular surfaces: flat, concave and convex surfaces.<ref name="Platzer2008p28"/> Types of articular surfaces include [[wikt:trochlear|trochlear]] surfaces.<ref>Armen S Kelikian, Shahan Sarrafian [https://books.google.com/books?id=I8h6bDR0SLMC&pg=PA94 ''Sarrafian's Anatomy of the Foot and Ankle: Descriptive, Topographic, Functional''] p.&nbsp;94</ref>

===Biomechanical classification===
Joints can also be classified based on their anatomy or on their biomechanical properties. According to the anatomic classification, joints are subdivided into ''simple'' and ''compound'', depending on the number of bones involved, and into ''complex'' and ''combination'' joints:<ref name="titleIntroductory Anatomy: Joints">{{cite web |url=http://www.leeds.ac.uk/chb/lectures/anatomy4.html |title=Introductory Anatomy: Joints |access-date=2008-01-29 |archive-date=2008-01-18 |archive-url=https://web.archive.org/web/20080118135754/http://www.leeds.ac.uk/chb/lectures/anatomy4.html |url-status=dead }}</ref>
# Simple joint: two articulation surfaces (e.g. [[shoulder joint]], [[hip joint]])
# Compound joint: three or more articulation surfaces (e.g. [[radiocarpal joint]])
# Complex joint: two or more articulation surfaces and an [[articular disc]] or [[meniscus (anatomy)|meniscus]] (e.g. [[knee|knee joint]])

===Anatomical=== <!--joint groups redirects here-->
[[File:Joints 1 -- Smart-Servier.png|thumb|Joints of the human body]]
The joints may be classified anatomically into the following groups:
# [[Joints of hand]]
# [[Elbow|Elbow joints]]
# [[Wrist|Wrist joints]]
# [[Axillary joints]]
# [[Sternoclavicular joint]]s
# [[Vertebral articulation]]s
# [[Temporomandibular joint]]s
# [[Sacroiliac joint]]s
# [[Hip joint]]s
# [[Knee|Knee joint]]s
# [[Articulations of foot]]

[[Axon|Unmyelinated nerve fibers]] are abundant in joint capsules and ligaments, as well as in the outer part of intra-articular menisci. These nerve fibers are responsible for pain perception when a joint is strained.<ref>{{Cite web|url=https://www.elsevier.com/books/clinical-neuroanatomy-and-neuroscience/mtui/978-0-7020-3738-2|title=Clinical Neuroanatomy and Neuroscience - 6th Edition|website=www.elsevier.com|access-date=2019-03-17}}</ref>