Download No. 2 The Introduction of Arthrology

No. 2
The Introduction
of Arthrology
Chapter 2 Arthrology
Section 1 Introduction
The bones are connected together by
fibrous, cartilaginous or osseous tissues at
different parts of their surfaces, and such
a connection is designated by the name of
joint or articulation.
 According to the movement they are
classified into two types of joints, i.e.
synarthroses (syn=together; arthron=joint)
and diarthroses.

Ⅰ. Synarthroses
The
synarthroses
(immovable
articulations) include the fibrous joints,
the cartilaginous joints and synostoses.
However, slight movement is, in fact,
permitted in some synarthroses.
Ⅰ) The Fibrous Joints
The fibrous joints include all the
articulations in which the bones are held
tightly together by fibrous connective
tissue. The bones are united by fibrous
tissue without any cavity. There are two
types of fibrous joints, sutures and
syndesmoses, depending in part on the
length of the connective tissue fibers that
hold the bones together.
1. Sutures
The separated bones are held together
by a thin layer of fibrous tissue. The union
is extremely tight and there is little or no
movement between the bones. This kind
of joint is found only between the flat
bones of the skull and can be fused by
ossification from the early 20s and
progresses throughout the life.
2. Syndesmoses
The bones are united by a ligament
or a sheet of fibrous tissue, e.g., the
yellow ligaments join the adjacent two
vertebral arches, and the interoseous
membrane joins the radius with the ulna.
Bones joined by syndesmoses are not
held as firmly as those joined by sutures.
Syndesmoses can permit some movement.
Ⅱ) Cartilaginous Joints
The bones are united by cartilage. They
allow little or no movement.
There are two types of cartilaginous
joints:
synchondroses
symphyses.
1. Synchondroses
The bones of a synchondrosis joint are
jointed by hyaline cartilage.For example, the
epiphysial cartilage plate connects the ends and
the shaft of a long bone.
Many synchondroses are temporary joints,
with the cartilage eventually being replaced by
bone. This replacement occurs between the
epiphyses and the diaphysis of long bones
(where the epiphyseal cartilages are replaced)
and between certain skull bones. The joints
formed between the first ten ribs and their costal
cartilages are permanent synchondroses.
2. Symphyses
The connecting material is a broad, flat
disc of fibrocartilage.
This kind of joint is found between the
bodies of vertebrae. The pubic symphysis
is another example of these joints. The
symphysis does not ossify throughout the
life.
Ⅲ) Synostoses
The bones are united by the
ossification of the fibrous joint or
synchondrosis between them, e.g., the
synostoses between the ilium, ischium
and pubis of the hip bone.
Ⅱ. Diarthroses
The Diarthroses (movable articulations,
synovial joints) there is a space between the
articulating bones, called the synovial cavity.
This kind of joints normally provide free
movement.
The bones are connected by the joint capsule
and ligament. There is a space between the
articulating bones, called the synovial cavity.
This kind of joints normally provide free
movement. We called them as Synovial Joints
Ⅰ) The Essential Structures of a
Synovial Joint
The essential structures are as follows:
Articular surface,
Articular capsule,
Articular cavity.
1. The articular surfaces
They are usually covered by the articular
cartilage. The articular cartilage is a
thin layer of hyaline cartilage that covers
the smooth articular surfaces of the bones.
It is very smooth but uneven in the
thickness.


2. The articular (joint) capsule
The articular capsule is a double-layered
membrane that surrounds and encloses the
joint. It is attached to the periphery of the
articular surface and adjacent bone surface.
The outer layer of the capsule (fibrous
membrane) is formed by dense connective
tissue whose fibers are firmly joined to the
periosteum of the bones and is riched in blood
vessels and nerves. Its thickness is
corresponding to the functions of the joint.

The inner layer of the articular capsule is
referred to as the synovial membrane. It
consists of lose connective tissue whose inner
surface is well supplied with capillaries. The
membrane, which is often thrown into folds
that project into the joint cavity, invests the
inside of the fibrous membrane, except for the
surface of the articular cartilages. It is very
thin, glistening and slippery.
The synovial membrane secretes a thick
fluid called synovial fluid (synovia). Synovial
fluid provides nourishment to the articular
cartilages, and lubricates the joint surfaces.
3. The articular (joint) cavity
It is a closed cavity formed by the
synovial membrane and the articular cartilage.
It contains a proper amount of synovia. Its
pressure is negative to the atmosphere pressure.
Ⅱ) The Accessory Structures of
Synovial Joints
The accessory structures are as follows:
The ligaments
The articular disc (or cartilage)
The articular labrum (lip)
1. The ligaments
The joints are usually strengthened by
accessory ligaments which are either
inside or outside the joint (the
intracapsular and extracapsular ligament).
These ligaments are designed to limit
movements of the joint in undesirable
direction.
2. The articular disc (or cartilage)
It is usually a fibrocartilage and divides the
joint cavity
partially or completely into two
parts.
Functions: It makes the articular surfaces
more fitting with each other and diminishes the
shock of the joint.
3. The articular labrum (lip)
It is a pliable, fibrocartilaginous ring that
helps to deepen the articular surface for the
bones, e.g., the labrum of the glenoid cavity of
the scapula.
Ⅲ) The Movement of Joint
The basic movements of joints are as follows:
1. Flexion and extension
2. Adduction and abduction
3. Rotation
4. Circumduction
1. Flexion and extension
These two antagonistic movements are
performed in the coronal axis.
The flexion decreases the angle between the
adjoining bones,
whereas the extension
increases the angle.
2. Adduction and abduction
The movements are perfomed in the sagittal axis.
The adduction means the movement of a bone
toward the midline of the body.
The abduction means the movement of a part
away from the midline of the body.
3. Rotation
It means moving a bone around its vertical axis.
It includes medial rotation and lateral rotation.
Pronation and supination:
The movements are specially for the forearm.
The pronation is a movement of the forearm in which the
palm of the hand is turned backward.
The supination is the movement in which the palm is
turned forward.
4. Circumduction
It is a movement in which the distal end of a bone moves
in a circle while the position of proximal end remains
relatively stable.
Ⅳ) The types of Synovial Joints
They can be classified according to the
number of bones, the axis and the type of
movement or the shape of articular surface etc.
1. The uniaxial joints
They permit movement only in one axis (coronal,
sagittal or vertical).
1) The hinge joints (or trochlear joints)
They permit flexion and extension, e.g., the
interphalangeal joints.
2) The pivot joints
They allow rotation around a long axis, e.g., the
proximal radioulnar joint permits rotation of the
head of radius.
2. The biaxial joints
They allow movement in two axes which meet at
right angle to each other.
1) The ellipsoid joints (or condyloid joints) They
permit flexion and extension, adduction and
abduction, as well as circumduction. Their articular
surfaces are ellipsoidal or oval in shape, e.g., the
radiocarpal joint.
2) The saddle joints
Their articular surfaces are concave and convex,
opposite to each other.
They allow movement of flexion, extention,
adduction, abduction and circumduction. The
carpometacarpal joint of the thumb is a good example.
3. The multiaxial joints
1) The plane joints (or gliding joint)
Some of these joints are referred to the multiaxial
joints. But they permit only a little of movement, e.g.,
the acromioclavicular joint.
2) The ball and socket joints
They are the most freely moving synovial joints.
Universal movements are permitted (i.e., in an almost
infinite number of axes), such as flexion and
extension, adduction and abduction, medial and
lateral rotation, and circumductiom, for example, the
shoulder and hip joints.