Editing Synovial joint (section)

== Structure ==
Synovial joints contain the following structures:
* Synovial cavity: all diarthroses have the characteristic space between the bones that is filled with [[synovial fluid]].
* [[Joint capsule]]: the fibrous capsule, continuous with the periosteum of articulating bones, surrounds the diarthrosis and unites the articulating bones; the joint capsule consists of two layers - (1) the outer [[Fibrous connective tissue|fibrous]] membrane that may contain ligaments and (2) the inner [[synovial membrane]] that secretes the lubricating, shock absorbing, and joint-nourishing synovial fluid; the joint capsule is highly innervated, but without blood and lymph vessels, and receives nutrition from the surrounding blood supply via either [[diffusion]] (slow), or via [[convection]] (fast, more efficient), induced through exercise.
* [[Articular cartilage]]: the bones of a synovial joint are covered by a layer of [[hyaline cartilage]] that lines the [[Epiphysis|epiphyses]] of the joint end of the bone with a smooth, slippery surface that prevents [[adhesion]]; articular cartilage functions to absorb shock and reduce [[friction]] during movement.

Many, but not all, synovial joints also contain additional structures:<ref name="Graysp20"/>
* [[Articular disc]]s or menisci - the [[fibrocartilage]] pads between opposing surfaces in a joint
* Articular fat pads - [[adipose tissue]] pads that protect the articular cartilage, as seen in the infrapatellar fat pad in the knee
* [[Tendons]]<ref name="Graysp20"/> - cords of [[dense regular connective tissue]] composed of parallel bundles of [[collagen fibers]]
* Accessory ligaments (extracapsular and intracapsular) - the fibers of some fibrous membranes are arranged in parallel bundles of dense regular connective tissue that are highly adapted for resisting strains to prevent extreme movements that may damage the articulation{{Citation needed|date=October 2012}}
* [[Bursae]] - sac-like structures that are situated strategically to alleviate friction in some joints (shoulder and knee) that are filled with fluid similar to synovial fluid<ref name="Tortora12thEd"/>{{Page needed|date=October 2012}}

The bone surrounding the joint on the proximal side is sometimes called the ''plafond'' (French word for ceiling), especially in the [[talocrural joint]]. Damage to this structure is referred to as a [[Gosselin fracture]].

===Blood supply===
The blood supply of a synovial joint is derived from the arteries sharing in the [[anastomosis]] around the joint.

=== Types ===
There are seven types of synovial joints.<ref name="umich2010couse"/> Some are relatively immobile, therefore more stable. Others have multiple degrees of freedom, but at the expense of greater risk of injury.<ref name="umich2010couse"/> In ascending order of mobility, they are:

{| class="wikitable"
! Name
! Example
! Description
|- 
| [[Plane joint]]s<br/>(or gliding joint) 
| [[carpal]]s of the [[wrist]], [[acromioclavicular joint]]
| These joints allow only gliding or sliding movements, are multi-axial such as the articulation between vertebrae.
|- 
| [[Hinge joint]]s
| [[Elbow-joint|elbow]] (between the [[humerus]] and the [[ulna]])
| These joints act as a [[door]] [[hinge]] does, allowing flexion and extension in just one plane, i.e. uniaxial.
|-
| [[Pivot joint]]s
| [[atlanto-axial joint]], [[proximal radioulnar joint]], and [[distal radioulnar joint]]
| One bone rotates about another
|- 
| [[Condyloid joint]]s<br/>(or ellipsoidal joints)
| [[wrist joint]] ([[radiocarpal joint]])
| A condyloid joint is a modified ball and socket joint that allows primary movement within two perpendicular axes, passive or secondary movement may occur on a third axes. Some classifications make a distinction between condyloid and ellipsoid joints;<ref name="Rogers2010p157"/><ref name="Sharkey2008p33"/> these joints allow flexion, extension, abduction, and adduction movements (circumduction).  
|- 
| [[Saddle joint]]s
| [[Carpometacarpal]] or trapeziometacarpal joint of [[thumb]] (between the [[metacarpal]] and [[carpal]] - [[trapezium (bone)|trapezium]]), [[sternoclavicular joint]]
| Saddle joints, where the two surfaces are reciprocally concave/convex in shape, which resemble a [[horse tack|saddle]], permit the same movements as the condyloid joints but allows greater movement.
|- 
| {{nowrap|[[Ball and socket joint]]s}}<br/>"universal Joint"
| [[shoulder]] ([[glenohumeral]]) and [[hip]] joints
| These allow for all movements except gliding
|- 
| Compound joints<ref name="Moini2011p231"/><ref name="Abernethy2005p331"/><br/>/ bicondyloid joints<ref name="Graysp20"/>
| [[knee]] joint
| condylar joint (condyles of femur join with condyles of tibia) and saddle joint (lower end of femur joins with patella)
|}

====Multiaxial joints====
[[File:903 Multiaxial Joint.jpg|thumb|A multiaxial joint, such as the hip joint, allows for three types of movement: anterior-posterior, medial-lateral, and rotational.]]
A '''multiaxial joint''' ('''polyaxial joint''' or '''triaxial joint''') is a synovial joint that allows for several directions of movement.<ref>{{cite web |last1=Miles |first1=Linda |title=LibGuides: BIO 140 - Human Biology I - Textbook: Chapter 41 - Classification of Joints |url=https://guides.hostos.cuny.edu/bio140/12-41 |website=guides.hostos.cuny.edu |publisher=Hostos Community College Library |access-date=21 May 2023 |language=en}}</ref> In the human body, the [[shoulder joint|shoulder]] and [[hip joint]]s are multiaxial joints.<ref>{{cite book |last1=Lawry |first1=George V. |title=Chapter 1 - Anatomy of Joints, General Considerations, and Principles of Joint Examination |chapter=Anatomy of Joints, General Considerations, and Principles of Joint Examination |chapter-url=https://www.sciencedirect.com/science/article/abs/pii/B9780323030038500052 |website=Musculoskeletal Examination and Joint Injection Techniques |publisher=Mosby |access-date=21 May 2023 |pages=1–6 |language=en |date=1 January 2006|doi=10.1016/B978-0-323-03003-8.50005-2 |isbn=978-0-323-03003-8 }}</ref> They allow the upper or lower limb to move in an anterior-posterior direction and a medial-lateral direction. In addition, the limb can also be rotated around its long axis. This third movement results in rotation of the limb so that its anterior surface is moved either toward or away from the midline of the body.<ref name="ana&physio">{{cite book |last1=Betts |first1=J. Gordon |title=Anatomy & physiology |date=2013 |publisher=OpenStax |chapter=9.1 Classification of joints|location=Houston, Texas |isbn=978-1-947172-04-3 |url=https://openstax.org/books/anatomy-and-physiology/pages/9-1-classification-of-joints |access-date=14 May 2023}}</ref>