Fibrous Joint .
The bones are joined by fibrous tissue in fibrous joints . These joints are either immovable or permit a slight degree of movement. These can be grouped in the following three subtypes.
1. Sutures:-
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| Types of sutures |
These are peculiar to skull, and are immovable. According to the shape of bony margins, the sutures can be:
(i) Plane, e.g. internasal suture .
(ii) Serrate, e.g. interparietal suture .
(iii) Squamous, e.g. Temporo-parietal suture .
(iv) Denticulate, e.g. lambdoid suture .
(v) Schindylesis type , e.g. between rostrum of sphenoid and upper border of vomer.
Neonatal skull reveals fontanelles which are temporary in nature. At six specific points on the sutures in new born skull are membrane filled gaps called “fontanelles”. These allow the underlying brain to increase in size. Anterior fontanelle is used to judge the hydration of the infant. All these fontanelles become bone by 18 months .
2. Syndesmosis:-
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| Syndesmosis: – Inferior tibiofibular joint |
The bones are connected by the interosseous ligament. Example: inferior tibiofibular joint .
3. Gomphosis (peg and socket joint) :-
Example: root of the tooth in
its bony socket .
Cartilaginous Joint .
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| Primary cartilaginous joint |
The bones are joined by cartilage in this type of joints . These are of the
following two types:-
1. Primary cartilaginous joints (synchondrosis or hyaline cartilage
joints): –
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 bone (synostosis).
Examples:-
(a) Joint between epiphysis and diaphysis of a growing long bone .
(b) Spheno-occipital joint .
(c) First chondrosternal joint .
(d) Costochondral joints .
2. Secondary cartilaginous joints (symphyses or fibrocartilaginous
joints):-
The articular surfaces are covered by a thin layer of hyaline
cartilage, and united by .a disc of fibrocartilage.
These joints are permanent and persist throughout life. In this
respect symphysis menti is a misnomer as it is a synostosis.
Typically the secondary cartilaginous joints occur in the median
plane of the body, and permit limited movements due to
compressible pad of fibro-cartilage such as in the pubic symphysis
and manubriosternal joints.
The thickness of fibrocartilage is directly related to the range of
movement. Secondary cartilaginous joints may represent an
intermediate stage in the evolution of synovial joints.
Examples :-
(a) Symphysis pubis .
(b) Manubriosternal joint .
(c) Intervertebral joints between the vertebral bodies .
Synovial Joint .
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| Simple synovial joint |
Features of Synovial Joint .
1. The articular surfaces are covered with hyaline (articular) cartilage
(fibrocartilage in certain membrane bones).
Articular cartilage is avascular, non-nervous and elastic.
Lubricated with synovial fluid, the cartilage provides slippery
surfaces for free movements, like ‘ice on ice’.
The surface of the cartilage shows fine undulations filled with
synovial fluid.
2. 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 or meniscus .
3. The joint is surrounded by an articular capsule which is made up
of a fibrous capsule lined by synovial membrane.
Because of its rich nerve supply, the fibrous capsule is sensitive
to stretches imposed by movements. This sets up appropriate
reflexes to protect the joint from any sprain. This is called the
‘watch-dog’ action of the capsule.
The fibrous capsule is often reinforced by :-
(a) Capsular or true ligaments representing thickenings of the
fibrous capsule .
(b) The accessory ligaments (distinct from fibrous capsule) which
may be intra or extracapsular.
” Synovial Membrane ”
The synovial membrane lines whole of the interior of the joint,
except for the articular surfaces covered by hyaline cartilage.
The membrane secretes a slimy viscous fluid called the synovia
or synovial fluid which lubricates the joint and nourishes the
articular cartilage. The viscosity of fluid is due to hyaluronic acid
secreted by cells of the synovial membrane.
4. Varying degrees of movements are always permitted by the
synovial joints .
Classification of Synovial Joint .
[A] Plane Synovial Joint .
Articular surfaces are more or less flat (plane). They permit gliding
movements (translations) in various directions.
Examples:-
(a) Intercarpal joints .
(b) Intertarsal joints .
(c) Joints between articular processes of vertebrae .
(d) Cricothyroid joint .
(e) Cricoarytenoid joint .
(f) Superior tibiofibular .
(g) Interchondral joint (5-9 ribs) .
(h) Costovertebral .
(i) Costotransverse .
(j) Acromioclavicular with intra-articular disc .
(k) Carpometacarpal (except first) .
(1) Tarsometatarsal .
(m) Intermetacarpal .
(n) Intermetatarsal .
(o) Chondrosternal (except first) .
(p) Sacroiliac .
[B].Hinge Joints (Ginglymi) .
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| Hinge Joints:-Elbow joint |
Articular surfaces are pulley-shaped. There are strong collateral
ligaments. Movements are permitted in one plane around a transverse
axis.
Examples:-
(a) Elbow joint .
(b) Ankle joint .
(c) Interphalangeal joints .
[C]. Pivot (Trochoid) Joints .
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| Pivot (Trochoid) Joints :- Radioulnar joints |
Articular surfaces comprise a central bony pivot (peg) surrounded by an osteoligamentous ring. Movements are permitted in one plane around a vertical axis.
Examples:-
(a) Superior and inferior radio-ulnar joints .
(b) Median atlanto-axial joint .
[D].Condylar (Bicondylar) Joints .
Articular surfaces include two distinct condyles (convex male surfaces)
fitting into reciprocally concave female surfaces (which are also,
sometimes known as condyles, such as in tibia). These joints permit
movements mainly in one plane around a transverse axis, but partly in
another plane (rotation) around a vertical axis.
Examples:-
(a) Knee joint .
(b) Right and left jaw joints or temporomandibular joint .
[E]. Ellipsoid Joints .
Articular surfaces include an oval, convex, male surface fitting into an
elliptical, concave female surface. Free movements are permitted
around both the axes, flexion and extension around the transverse axis,
and abduction and adduction around the anteroposterior axis.
Combination of movements produces circumduction. Typical rotation
around a third (vertical) axis does not occur.
Examples:-
(a) Wrist joint .
(b) Metacarpophalangeal joints .
(c) Atlanto-occipital joints .
[F]. Saddle (Sellar) Joints .
Articular surfaces are reciprocally concavo-convex. Movements are
similar to those permitted by an ellipsoid joint with addition of some
rotation (conjunct rotation) around a third axis which however cannot
occur independently.
Examples:-
(a) First carpometacarpal joint .
(b) Sternoclavicular joint .
(c) Calcaneocuboid joint .
(d) Incudomalleolar joint .
(e) Between femur and patella .
[G]. Ball-and-Socket (Spheroidal) Joints .
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| Hip joint: Ball and socket variety |
Articular surfaces include a globular head (male surface) fitting into a
cup-shaped socket (female surface). Movements occur around an
indefinite number of axes which have one common centre. Flexion,
extension, abduction, adduction, medial rotation, lateral rotation and
circumduction, all occur quite freely.
Examples:-
(a) Shoulder joint .
(b) Hip joint .
(c) Talocalcaneonavicular joint .
(d) Incudostapedial joint .
