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A joint or articulation (or articular surface) is the connection made between
bone A bone is a rigid organ Organ may refer to: Biology * Organ (biology), a part of an organism Musical instruments * Organ (music), a family of keyboard musical instruments characterized by sustained tone ** Electronic organ, an electronic ...
s,
ossicles The ossicles (also called auditory ossicles) are three bones in either middle ear that are among the smallest bones in the human body. They serve to transmit sounds from the air to the fluid-filled labyrinth (inner ear), labyrinth (cochlea). The ...
, or other hard structures in the body which link an animal's
skeletal system A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...
into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw-Hill Connect. Web
p.274
/ref> They are constructed to allow for different degrees and types of movement. Some joints, such as the
knee In humans and other primates, the knee joins the thigh with the human leg, leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur and patella (patellofemoral joint). It is the largest join ...
,
elbow The elbow is the region between the arm and the forearm that surrounds the elbow joint. The elbow includes prominent landmarks such as the olecranon, the cubital fossa (also called the chelidon, or the elbow pit), and the Lateral epicondyle of ...
, and
shoulder The human shoulder is made up of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone) as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder mak ...
, are self-lubricating, almost frictionless, and are able to withstand compression and maintain heavy loads while still executing smooth and precise movements. Other joints such as sutures between the bones of the
skull The skull is a bone protective Cranial cavity, cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible ...
permit very little movement (only during birth) in order to protect the brain and the
sense organ A sense is a biological system used by an organism for sensation, the process of gathering information about the world through the detection of Stimulus (physiology), stimuli. (For example, in the human body, the brain which is part of the cen ...
s. 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.


Classification

The number of joints depends on if 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. 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)

Structural classification names and divides joints according to the type of binding tissue that connects the bones to each other. There are four structural classifications of joints: *
fibrous joint In anatomy, fibrous joints are joints connected by Fibrous connective tissue, fibrous tissue, consisting mainly of collagen. These are fixed joints where bones are united by a layer of white fibrous tissue of varying thickness. In the skull the j ...
– joined by dense regular connective tissue that is rich in collagen fibersPrinciples of Anatomy & Physiology, 12th Edition, Tortora & Derrickson, Pub: Wiley & Sons *
cartilaginous joint Cartilaginous joints are connected entirely by cartilage (fibrocartilage or hyaline). Cartilaginous joints allow more movement between bones than a fibrous joint but less than the highly mobile synovial joint. Cartilaginous joints also forms the ...
– joined by
cartilage Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the Epiphysis, ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, th ...
. There are two types: primary cartilaginous joints composed of
hyaline cartilage Hyaline cartilage is the glass-like (hyaline) and translucent cartilage found on many joint surfaces. It is also most commonly found in the ribs, nose, larynx, and trachea. Hyaline cartilage is pearl-gray in color, with a firm consistency and has ...
, and secondary cartilaginous joints composed of hyaline cartilage covering the articular surfaces of the involved bones with
fibrocartilage Fibrocartilage consists of a mixture of white fibrous tissue and cartilaginous tissue in various proportions. It owes its inflexibility and toughness to the former of these constituents, and its Elasticity (physics), elasticity to the latter. It ...
connecting them. *
synovial joint A synovial joint, also known as diarthrosis, joins bones or cartilage with a fibrous joint capsule that is continuous with the periosteum of the joined bones, constitutes the outer boundary of a synovial cavity, and surrounds the bones' articulat ...
– 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. *
facet joint The facet joints (or zygapophysial joints, zygapophyseal, apophyseal, or Z-joints) are a set of synovial joint, synovial, plane joints between the articular processes of two adjacent vertebrae. There are two facet joints in each functional spin ...
– joint between two articular processes between two vertebrae.


Functional classification (movement)

Joints can also be classified functionally according to the type and degree of movement they allow: Joint movements are described with reference to the basic
anatomical planes An anatomical plane is a hypothetical plane used to transect the body, in order to describe the location of structures or the direction of movements. In human and animal anatomy, three principal planes are used: * The sagittal plane The sa ...
. *
synarthrosis A synarthrosis is a type of joint which allows no movement under normal conditions. Sutures of skull, Sutures and gomphoses are both synarthroses. Joints which allow more movement are called Amphiarthrosis, amphiarthroses or diarthroses. Syndesmose ...
– permits little or no mobility. Most synarthrosis joints are
fibrous joint In anatomy, fibrous joints are joints connected by Fibrous connective tissue, fibrous tissue, consisting mainly of collagen. These are fixed joints where bones are united by a layer of white fibrous tissue of varying thickness. In the skull the j ...
s (e.g., skull sutures). *
amphiarthrosis Amphiarthrosis is a type of continuous, slightly movable joint. Types In amphiarthroses, the contiguous bony surfaces can be: * A symphysis: connected by broad flattened disks of fibrocartilage, of a more or less complex structure, which adhere t ...
– permits slight mobility. Most amphiarthrosis joints are
cartilaginous joint Cartilaginous joints are connected entirely by cartilage (fibrocartilage or hyaline). Cartilaginous joints allow more movement between bones than a fibrous joint but less than the highly mobile synovial joint. Cartilaginous joints also forms the ...
s (e.g.,
intervertebral disc An intervertebral disc (or intervertebral fibrocartilage) lies between adjacent vertebrae in the vertebral column. Each disc forms a fibrocartilaginous joint (a symphysis), to allow slight movement of the vertebrae, to act as a ligament to hold t ...
s). *
synovial joint A synovial joint, also known as diarthrosis, joins bones or cartilage with a fibrous joint capsule that is continuous with the periosteum of the joined bones, constitutes the outer boundary of a synovial cavity, and surrounds the bones' articulat ...
(also known as a ''diarthrosis'') – freely movable. Synovial joints can in turn be classified into six groups according to the type of movement they allow:
plane joint A plane joint (arthrodial joint, gliding joint, plane articulation) is a synovial joint which, under physiological conditions, allows only gliding movement. Plane joints permit sliding movements in the plane of articular surfaces. The opposed sur ...
,
ball and socket joint The ball-and-socket joint (or spheroid joint) is a type of synovial joint in which the ball-shaped surface of one rounded bone fits into the cup-like depression of another bone. The distal bone is capable of motion around an indefinite number of ...
,
hinge joint A hinge joint (ginglymus or ginglymoid) is a bone joint in which the articular surfaces are molded to each other in such a manner as to permit motion only in one plane. According to one classification system they are said to be uniaxial (having ...
,
pivot joint In animal anatomy, a pivot joint (trochoid joint, rotary joint or lateral ginglymus) is a type of synovial joint whose axis of rotation, movement axis is parallel to the anatomical terms of location#Axes, long axis of the proximal bone, which typic ...
,
condyloid joint A condyloid joint (also called condylar, ellipsoidal, or bicondylar) is an ovoid articular surface, or condyle (anatomy), condyle that is received into an elliptical cavity. This permits movement in two planes, allowing flexion, Extension (kinesi ...
and saddle joint. 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. Another classification is according to the degrees of freedom allowed, and distinguished between joints with one, two or three degrees of freedom. A further classification is according to the number and shapes of the articular surfaces: flat, concave and convex surfaces. Types of articular surfaces include trochlear surfaces.


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: # Simple joint: two articulation surfaces (e.g.
shoulder joint The shoulder joint (or glenohumeral joint from Greek ''glene'', eyeball, + -''oid'', 'form of', + Latin ''humerus'', shoulder) is structurally classified as a synovial joint, synovial ball-and-socket joint and functionally as a diarthrosis and mu ...
,
hip joint In vertebrate anatomy, hip (or "coxa"Latin ''coxa'' was used by Celsus in the sense "hip", but by Pliny the Elder in the sense "hip bone" (Diab, p 77) in medical terminology) refers to either an anatomical region or a joint. The hip region is ...
) # Compound joint: three or more articulation surfaces (e.g. radiocarpal joint) # Complex joint: two or more articulation surfaces and an
articular disc The articular disk (or disc) is a thin, oval plate of fibrocartilage present in several joints which separates synovial cavities. This separation of the cavity space allows for separate movements to occur in each space. The presence of an articula ...
or meniscus (e.g.
knee joint In humans and other primates, the knee joins the thigh with the human leg, leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur and patella (patellofemoral joint). It is the largest join ...
)


Anatomical

The joints may be classified anatomically into the following groups: # Joints of hand # Elbow joints # Wrist joints # Axillary joints #
Sternoclavicular joint The sternoclavicular joint or sternoclavicular articulation is a synovial saddle The saddle is a supportive structure for a rider of an animal, fastened to Mammal#Anatomy, an animal's back by a girth (tack), girth. The most common type ...
s # Vertebral articulations #
Temporomandibular joint In anatomy, the temporomandibular joints (TMJ) are the two joints connecting the jawbone to the skull. It is a bilateral Synovial joint, synovial articulation between the temporal bone of the skull above and the Human mandible, mandible below; ...
s #
Sacroiliac joint The sacroiliac joint or SI joint (SIJ) is the joint A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional wh ...
s #
Hip joint In vertebrate anatomy, hip (or "coxa"Latin ''coxa'' was used by Celsus in the sense "hip", but by Pliny the Elder in the sense "hip bone" (Diab, p 77) in medical terminology) refers to either an anatomical region or a joint. The hip region is ...
s #
Knee joint In humans and other primates, the knee joins the thigh with the human leg, leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur and patella (patellofemoral joint). It is the largest join ...
s # Articulations of foot Unmyelinated nerve fibers are abundant in joint capsules and ligaments as well as in the outer part of intraarticular menisci. These nerve fibers are responsible for pain perception when a joint is strained.


Clinical significance

Damaging the cartilage of joints (
articular cartilage Hyaline cartilage is the glass-like (hyaline) and translucent cartilage Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the Epiphysis, ends of long bones at the joints as articular cartilage, a ...
) or the bones and muscles that stabilize the joints can lead to
joint dislocation A joint dislocation, also called luxation, occurs when there is an abnormal separation in the joint, where two or more bones meet.Dislocations. Lucile Packard Children’s Hospital at Stanford. Retrieved 3 March 2013 A partial dislocation is refer ...
s and osteoarthritis. Swimming is a great way to exercise the joints with minimal damage. A joint disorder is termed arthropathy, and when involving
inflammation Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells, blood vessels, and mol ...
of one or more joints the disorder is called
arthritis Arthritis is a term often used to mean any disorder that affects joints. Symptoms generally include joint pain and stiffness. Other symptoms may include redness, warmth, Joint effusion, swelling, and decreased range of motion of the affected j ...
. Most joint disorders involve arthritis, but joint damage by external
physical trauma An injury is any physiological damage to living tissue caused by immediate physical stress. An injury can occur intentionally or Accident, unintentionally and may be caused by blunt trauma, penetrating trauma, burning, Toxin, toxic exposure, asp ...
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 Osteoarthritis (OA) is a type of degenerative joint disease that results from breakdown of articular cartilage, joint cartilage and underlying bone which affects 1 in 7 adults in the United States. It is believed to be the fourth leading cause of ...
(also known as degenerative joint disease), occurs following trauma to the joint, following an
infection An infection is the invasion of tissue (biology), tissues by pathogens, their multiplication, and the reaction of host (biology), host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmiss ...
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 Rheumatoid arthritis (RA) is a long-term autoimmune disorder that primarily affects synovial joint, joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. Most commonly, the wrist and ...
and
psoriatic arthritis Psoriatic arthritis is a long-term inflammatory arthritis that occurs in people affected by the autoimmune disease An autoimmune disease is a condition arising from an abnormal immune response to a functioning body part. At least 80 types o ...
, which are
autoimmune diseases An autoimmune disease is a condition arising from an abnormal immune response to a functioning body part. At least 80 types of autoimmune diseases have been identified, with some evidence suggesting that there may be more than 100 types. Nearly ...
in which the body is attacking itself.
Septic arthritis Acute septic arthritis, infectious arthritis, suppurative arthritis, osteomyelitis, or joint infection is the invasion of a joint by an infectious agent resulting in arthritis, joint inflammation. Generally speaking, symptoms typically include re ...
is caused by joint infection. Gouty arthritis is caused by deposition of
uric acid Uric acid is a heterocyclic compound of carbon, nitrogen, oxygen, and hydrogen with the Chemical formula, formula C5H4N4O3. It forms ions and salts known as urates and acid urates, such as ammonium acid urate. Uric acid is a product of the meta ...
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 Calcium pyrophosphate (Ca2P2O7) is a chemical compound, an insoluble calcium salt containing the pyrophosphate In chemistry, pyrophosphates are phosphorus oxyanions that contain two phosphorus atoms in a P–O–P linkage. A number of pyrophosp ...
. This form of gout is known as
pseudogout Calcium pyrophosphate dihydrate (CPPD) crystal deposition disease, also known as pseudogout and pyrophosphate arthropathy, is a rheumatology, rheumatologic disease which is thought to be secondary to abnormal accumulation of calcium pyrophosphate ...
. 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 In orthodontics, a malocclusion is a misalignment or incorrect relation between the teeth of the upper and lower dental arches when they approach each other as the jaws close. The English-language English is a West Germanic languages ...
), and may be affecting as many as 75 million Americans.


History


Etymology

The English word ''joint'' is a past participle of the verb ''join'', and can be read as ''joined''.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. Joint is derived from Latin ''iunctus'', past participle of the Latin verb ''iungere'', join, unite, connect, attach.Lewis, C.T. & Short, C. (1879). ''A Latin dictionary founded on Andrews' edition of Freund's Latin dictionary.'' Oxford: Clarendon Press. The English term ''articulation'' is derived from Latin ''articulatio''. Humans have also developed lighter, more fragile joint bones over time due to the decrease in physical activity compared to thousands of years ago.Thompson, Helen.
Switching to Farming Made Human Joint Bones Lighter
. ''Smithsonian Magazine''. Smithsonian, 22 December 2014. Retrieved 28 November 2016.


See also

* Arthrology * Cracking joints *
Kinesiology Kinesiology () is the scientific study of human body movement. Kinesiology addresses physiological, anatomical, Biomechanics, biomechanical, Pathology, pathological, neuropsychological principles and mechanisms of movement. Applications of kines ...
*
Ligament A ligament is the Connective tissue#Types, fibrous connective tissue that connects bones to other bones. It is also known as ''articular ligament'', ''articular larua'', ''fibrous ligament'', or ''true ligament''. Other ligaments in the body inc ...
* Replacement joint


References


External links


Synovial joints Illustrations and Classification
{{Authority control Skeletal system