General Anatomy of Joints: Classification of joints-Fibrous joints, Cartilaginous joints and Synovial Joints

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Classification of Joints (Viva, Short notes, Short Questions)
Structural classification:
Fibrous joints: (***short note)
In this type of joints the bones are joined together by fibrous tissue.
Due to the presence of fibrous tissue these joints are either immovable or permit movement
to a very little extent.
Fibrous joints are further divided into the following subtypes;
1. Sutures: These are peculiar to skull and are immovable. According to the shape of
the bony margin the sutures may be;
 Plane sutures
 Serrate sutures
 Denticulate sutures
 Squamous sutures
 Limbous sutures
 Schindylesis
Types of Sutures

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2. Syndesmosis: In this type of fibrous joints the bones are connected with
interosseus ligament for example the inferior tibiofibular joint and Interosseous
membrane between Radius and Ulna, Tibia and Fibula.
Inferior tibiofibular joint
3. Gomphosis: These are also known as peg and socket joints. Examples are tooth in
the socket.
Gomphosis (Teeth in their Sockets)

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Cartilaginous joints: (***short note)
In this type of joints there is a piece of cartilage between the bones which hold the bones
together and makes a joint.
Cartilaginous joints are further divided into the following subtypes;
1. Primary cartilaginous joints: (synchondrosis): In this subtype the bones are
united by a plate of hyaline cartilage so that the joint is immovable and strong.
These joints are temporary in nature because after a certain age the cartilaginous
plate is replaced by the bone. Examples of this type of joints are joint between the
epiphyses and diaphysis of a growing long bone (Epiphyseal Plate), the
costochondral joint and the first chondrosternal joint.
Joint between epiphysis and diaphysis with intervening epiphyseal plate of
cartilage
2. Secondary cartilaginous joints: (symphysis): These are also known as fibro-
cartilaginous joints. There articular surface is covered by a thin layer of hyaline
cartilage and the bones are united by fibro-cartilage.
These joints are permanent and persist throughout the life of an individual.
Typically the secondary cartilaginous joints occur in the median plane of the body
and permit limited movements because of compressible pad of cartilage in them.
The thickness of the fibro-cartilage in these joints is directly related to the range of
movement the joint offers. Examples of this type of joints are; symphysis pubis,
manubrio-sternal joint and intervertebral joints between the vertebral bodies.

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Symphysis Pubis
Synovial joints:
Synovial joints are most evolved and therefore most mobile type of joints.
Functional classification:
Immovable joints: (Synarthroses)
They are fixed joints at which there is no movement. The articular surfaces are joined by tough
fibrous tissue. Often the edges of the bones are dovetailed into one another as in the sutures of
the skull.
Partially moveable joints: (Amphiarthroses)
They are joints in which slight movement is possible. A pad of cartilage lies between the bone
surface and there is a fibrous capsule to hold the bone and cartilage in place. The cartilages of
such joints also act as shock absorbers for example the intervertebral discs between the bodies
of vertebrae where the cartilage is strengthened by extra collagen fibers.
Freely moveable joints: (Diarthroses)
They are the synovial joints of structural classification. They are freely moveable though at
some of them the movement is restricted by the shape of the articulating surfaces and by the
ligaments which hold them together. These ligaments are of elastic connective tissue.

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Structure of Synovial Joint (***short note)
A typical Synovial Joint (Image source: Madhero88/Wikipedia)
Synovial joints are most evolved and therefore most mobile type of joints. They possess the
following characteristic features;
 There articular surfaces are covered with hyaline cartilage. This articular cartilage
is avascular, non nervous and elastic. Lubricated with synovial fluid, the cartilage
forms slippery surfaces for free movements.
 Between the articular surfaces there is a joint cavity filled with synovial fluid. The
cavity may be partially or completely subdivided by an articular disc known as
meniscus.
 The joint is surrounded by an articular capsule which is fibrous in nature and is
lined by synovial membrane. Because of its rich nerve supply the fibrous capsule is
sensitive to stretches imposed by movements.
 The synovial membrane lines the entire joint except the articular surfaces
covered by hyaline cartilage. It is this membrane that secretes the slimy fluid called
synovial fluid which lubricates the joint and nourishes the articular cartilage.
 Varying degrees of movements are always permitted by the synovial joints.

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Types of synovial joints: (***short note, viva and Short Questions)
Scheme of Types of Synovial Joints (Image Source: Produnis/Wikipedia)
Synovial joints are of the following types;
Plane synovial joints:
The articular surfaces of plane synovial joints are more or less plane.
These joints permit gliding movements in various directions.
Examples are intercarpal joints, intertarsal joints, and joints between the articular processes of
vertebrae.

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Plane Synovial Joints of Carpus
Hinge joints:
In these joints the articular surfaces are pulley shaped.
There are strong collateral ligaments to provide stability to the joint.
Movements are permitted in one plane around a transverse axis.
Examples are elbow joint, ankle joint, interphaleangeal joint.
Hinge Joint (Elbow Joint)
Pivot joints:
Pivot joints are formed by a central bony pivot surrounded by an osteo-ligamentous ring.
Movements are permitted in one plane around a vertical axis. Examples of this type are
superior and inferior radioulnar joints and the median atlantoaxial joint.
Proximal Radioulnar Joint

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Condylar joints:
These are also known as bicondylar joints. There articular surfaces consist of two distinct
condyles in which one is convex surface (called the male surface) fitting into a concave
surface (called the female surface) of the other bone. These joints mainly permit the
movement in plane around a transverse axis. Example of this type of joints is knee joint, TM
joint.
Knee Joint (Posterior View)
Ellipsoid joints:
In this case the articular surfaces include an oval convex male surface fitting into an ellipsoid
female surface.
The movements are permitted around two axis; flexion and extension around the transverse
axis and adduction and abduction round antero-posterior axis.
Combination of these movements produces Circumduction.
Typical rotation around a third vertical axis does not occur.
Examples of this type of joints are wrist joint, metacarpophalangeal joint and atlanto-occipital
joint.

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Wrist Joint (ellipsoid Joint)
Saddle joints:
Articular surfaces are reciprocally concavo-convex.
Movements are similar to those permitted by ellipsoid joint with addition of some rotation
(conjunct rotation (rotation which accompany other movements)) around a third axis which
occurs independently.
Examples of this type of joints are first carpometacarpal joint, sternoclavicular joint,
calcaneocuboid joint.
Saddle Joint

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Ball and socket joints:
These are also called spheroidal joints.
There articular surfaces include a globular head fitting into a cup shaped socket.
Movement occurs around an indefinite number of axes which have common center.
Flexion, extension, abduction, adduction, rotation, Circumduction all occur quite freely.
Examples of this type of joints are shoulder joint, hip joint and talo-calcaneonavicular joint.
Ball and Socket Joint (Hip Joint)
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