View source for Joint

{{Short description|Location at which two or more bones make contact}}
{{other uses}}
{{Infobox anatomy
| Name        = Joint
| Latin       = articulus,<br />junctura,<br />articulatio
| Greek       = 
| Image       = Joint.svg
| Caption     = Diagram of a typical [[synovial joint]]
| Width       = 300
| Image2      = Gray298.png
| Caption2    = Depiction of an [[intervertebral disc]], a [[cartilaginous joint]]
| Precursor   = 
| System      = [[Musculoskeletal system]]<br />Articular system
| Artery      = 
| Vein        = 
| Nerve       = 
| Lymph       = 
}}
A '''joint''' or '''articulation''' (or '''articular surface''') is the connection made between [[bone]]s, [[ossicles]], or other hard structures in the body which link an animal's [[skeletal system]] into a functional whole.<ref name="Whiting2006p40">{{cite book |last1=Whiting |first1=William Charles |last2=Rugg |first2=Stuart |year=2006 |title=Dynamic Human Anatomy |volume=10 |url=https://books.google.com/books?id=ylyAXBPno2IC&pg=PA40 |pages=40|publisher=Human Kinetics |isbn=9780736036825 }}</ref><ref>{{cite web|url=http://www.emedicinehealth.com/script/main/art.asp?articlekey=8746|title=Articulation definition|publisher=eMedicine Dictionary|date=30 October 2013|access-date=18 November 2013|archive-date=31 July 2012|archive-url=https://web.archive.org/web/20120731092044/http://www.emedicinehealth.com/script/main/art.asp?articlekey=8746|url-status=dead}}</ref><ref name="Saladinp274">Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw-Hill Connect. Web. [http://connect.mheducation.com/connect/hmEBook.do?setTab=sectionTabs p.274]</ref> They are constructed to allow for different degrees and types of movement. Some joints, such as the [[knee]], [[elbow]], and [[shoulder]], are self-lubricating, almost frictionless, and are able to withstand compression and maintain heavy loads while still executing smooth and precise movements.<ref name="Saladinp274"/> Other joints such as [[suture (joint)|sutures]] between the bones of the [[skull]] permit very little movement (only during birth) in order to protect the brain and the [[sense organ]]s.<ref name="Saladinp274"/> The connection between a tooth and the [[jawbone]] is also called a joint, and is described as a fibrous joint known as a [[gomphosis]]. Joints are classified both structurally and functionally.<ref name="isbn0-443-07168-3">{{cite book|last1=Standring|first1=Susan|title=Gray's anatomy : the anatomical basis of clinical practice.|date=2006|publisher=Elsevier Churchill Livingstone|location=Edinburgh|isbn=0-443-07168-3|page=[https://archive.org/details/graysanatomyanat0000unse/page/38 38]|edition=39th|url=https://archive.org/details/graysanatomyanat0000unse/page/38}}</ref>

Joints play a vital role in the human body, contributing to movement, stability, and overall function. They are essential for mobility and flexibility, connecting bones and facilitating a wide range of motions, from simple bending and stretching to complex actions like running and jumping. Beyond enabling movement, joints provide structural support and stability to the skeleton, helping to maintain posture, balance, and the ability to bear weight during daily activities.

The clinical significance of joints is highlighted by common disorders that affect their health and function. '''Osteoarthritis''', a degenerative joint disease, involves the breakdown of cartilage, leading to pain, stiffness, and reduced mobility. '''Rheumatoid arthritis''', an autoimmune disorder, causes chronic inflammation in the joints, often resulting in swelling, pain, and potential deformity. Another prevalent condition, '''gout''', arises from the accumulation of uric acid crystals in the joints, triggering severe pain and inflammation.

Joints also hold diagnostic importance, as their condition can indicate underlying health issues. Symptoms such as joint pain and swelling may signal inflammatory diseases, infections, or metabolic disorders. Effective treatment and management of joint-related conditions often require a multifaceted approach, including physical therapy, medications, lifestyle changes, and, in severe cases, surgical interventions. Preventive care, such as regular exercise, a balanced diet, and avoiding excessive strain, is critical for maintaining joint health, preventing disorders, and improving overall quality of life.

==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|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>

==Clinical significance==
{{Further|Arthropathy|Arthritis|Joint replacement}}
Damaging the cartilage of joints ([[articular cartilage]]) or the bones and muscles that stabilize the joints can lead to [[joint dislocation]]s and osteoarthritis. Swimming is a great way to exercise the joints with minimal damage.<ref name="Saladinp274"/> Another potential intervention is the oral supplementation of type II collagen, glucosamine hydrochloride, and chondroitin sulfate improvin the quality of life.<ref>{{cite journal |last1=Fladerer-Grollitsch |first1=Johannes-Paul |last2=Klein |first2=Thomas |last3=Kompek |first3=Albert |last4=Steiner |first4=Nicole |last5=Menzel |first5=Daniel |last6=Schön |first6=Christiane |title=Effects of cartilage-supporting nutritional supplementation on knee osteoarthritis symptoms and quality of life in a 12-week randomized double-blind placebo-controlled pilot study |journal=Scientific Reports |date=15 July 2025 |volume=15 |issue=1 |doi=10.1038/s41598-025-11723-2}}</ref>

A joint disorder is termed [[arthropathy]], and when involving [[inflammation]] of one or more joints the disorder is called [[arthritis]]. Most joint disorders involve arthritis, but joint damage by external [[physical trauma]] is typically not termed arthritis.

Arthropathies are called ''polyarticular'' (multiarticular) when involving many joints and ''monoarticular'' when involving only a single joint.

Arthritis is the leading cause of disability in people over the age of 55. There are many different forms of arthritis, each of which has a different cause. The most common form of arthritis, [[osteoarthritis]] (also known as degenerative joint disease), occurs following trauma to the joint, following an [[infection]] of the joint or simply as a result of aging and the deterioration of articular cartilage. Furthermore, there is emerging evidence that abnormal anatomy may contribute to early development of osteoarthritis. Other forms of arthritis are [[rheumatoid arthritis]] and [[psoriatic arthritis]], which are [[autoimmune disorder|autoimmune diseases]] in which the body is attacking itself. [[Septic arthritis]] is caused by joint infection. [[Gout|Gouty arthritis]] is caused by deposition of [[uric acid]] crystals in the joint that results in subsequent inflammation. Additionally, there is a less common form of gout that is caused by the formation of rhomboidal-shaped crystals of [[calcium pyrophosphate]]. This form of gout is known as [[Chondrocalcinosis|pseudogout]].

[[Temporomandibular joint syndrome]] (TMJ) involves the jaw joints and can cause facial pain, clicking sounds in the jaw, or limitation of jaw movement, to name a few symptoms. It is caused by psychological tension and misalignment of the jaw ([[malocclusion]]), and may be affecting as many as 75 million Americans.<ref name="Saladinp274"/>

==History==

===Etymology===
The English word ''joint'' is a past participle of the verb ''join'', and can be read as ''joined''.<ref name="Klein1971">Klein, E. (1971). A comprehensive etymological dictionary of the English language. Dealing with the origin of words and their sense development thus illustration the history of civilization and culture. Amsterdam: Elsevier Science B.V.</ref> Joint is derived from Latin ''iunctus'',<ref name="Klein1971"/> past participle of the Latin verb ''iungere'', join, unite, connect, attach.<ref name="Lewis & Short">Lewis, C.T. & Short, C. (1879). ''A Latin dictionary founded on Andrews' edition of Freund's Latin dictionary.'' Oxford: Clarendon Press.</ref>

The English term ''articulation'' is derived from Latin ''articulatio''.<ref name="Klein1971"/>

Humans have also developed lighter, more fragile joint bones over time due to the decrease in physical activity compared to thousands of years ago.<ref name="Thompson2014">Thompson, Helen. "[http://www.smithsonianmag.com/science-nature/switching-farming-made-human-joint-bones-lighter-180953711/ Switching to Farming Made Human Joint Bones Lighter]". ''Smithsonian Magazine''. Smithsonian, 22 December 2014. Retrieved 28 November 2016.</ref>

==See also==

* [[Arthrology]]
* [[Cracking joints]]
* [[Kinesiology]]
* [[Ligament]]
* [[Development of joints]]

==References==
{{reflist}}

==External links==
{{Commons category|Joints|lcfirst=yes}}
* [http://www.sports-db.com/home/information/joints.html Synovial joints Illustrations and Classification]

{{Human systems and organs}}
{{Joints}}
{{Cranial fibrous joints}}
{{Joints of head and neck}}
{{Joints of torso}}
{{Joints of upper limbs}}
{{Joints of lower limbs}}

{{Authority control}}

[[Category:Joints| ]]
[[Category:Skeletal system]]