1.
joint

2.
JOINT CLASSIFICATIONS
● Joints are classified structurally, based on their anatomical characteristics,
and functionally, based on the type of movement they permit.
● The structural classification of joints is based on two criteria:
(1)The presence or absence of a space between the articulating bones, called a
synovial cavity, and
(2) the type of connective tissue that binds the bones together.

3.
● Structurally, joints are classified as one of the following types:
⮚ Fibrous joints: There is no synovial cavity, and the bones are held together
by dense irregular connective tissue that is rich in collagen fibers.
⮚ Cartilaginous joints: There is no synovial cavity and the bones are held
together by cartilage.
⮚ Synovial joints: The bones forming the joint have a synovial cavity and are
united by the dense irregular connective tissue of an articular capsule, and
often by accessory ligaments.

4.
● The functional classification of joints relates to the degree of movement
they permit.
● Functionally, joints are classified as one of the following types:
⮚ Synarthrosis : An immovable joint. The plural is synarthroses.
⮚ Amphiarthrosis : A slightly movable joint. The plural is amphiarthroses.
⮚ Diarthrosis : A freely movable joint. The plural is diarthroses.
● All diarthroses are synovial joints.

5.
1. FIBROUS JOINTS
❖ Sutures
● A suture is a fibrous joint composed of a thin layer of dense irregular
connective tissue; sutures occur only between bones of the skull.
● An example is the coronal suture between the parietal and frontal bones.
● The irregular, interlocking edges of sutures give them added strength and
decrease their chance of fracturing. Because a suture is immovable, it is
classified functionally as a synarthrosis.
● Some sutures that are present during childhood are replaced by bone in the
adult.

6.
● Such a suture is an example of a synostosis, or bony joint—a joint in which
there is a complete fusion of two separate bones into one bone.
● For example, the frontal bone grows in halves that join together across a
suture line.
● Usually they are completely fused by age 6 and the suture becomes obscure.
● If the suture persists beyond age 6, it icalled a metopic suture.
● A synostosis is also classified functionally as a synarthrosis.

7.
❖ Syndesmoses
● A syndesmosis is a fibrous joint in which there is a greater distance between
the articulating surfaces and more dense irregular connective tissue than in a
suture.
● The dense irregular connective tissue is typically arranged as a bundle and
the joint permits limited movement.
● One example of a syndesmosis is the distal tibiofibular joint, where the
anterior tibiofibular ligament connects the tibia and fibula.
● It permits slight movement.

8.
● Another example of a syndesmosis is called a gomphosis or dentoalveolar
joint, in which a cone-shaped peg fits into a socket.
● The only examples of gomphoses in the human body are the articulations
between the roots of the teeth and their sockets in the maxillae and mandible.
● The dense irregular connective tissue between a tooth and its socket is the
thin periodontal ligament.
● A gomphosis permits no movement.
● Inflammation and degeneration of the gums, periodontal ligament, and bone is
called periodontal disease.

9.
❖ Interosseous Membranes
● The final category of fibrous joint is the interosseous membrane, a
substantial sheet of dense irregular connective tissue that binds neighboring
long bones and permits slight movement.
● There are two principal interosseous membrane joints in the human body.
● One occurs between the radius and ulna in the forearm and the other
occurs between the tibia and fibula in the leg.

10.
2. CARTILAGINOUS JOINTS
● Like a fibrous joint, a cartilaginous joint lacks a synovial cavity and allows
little or no movement.
● Here the articulating bones are tightly connected by either hyaline cartilage or
fibrocartilage.
● The two types of cartilaginous joints are synchondroses and symphyses.
● A synchondrosis is a cartilaginous joint in which the connecting material is
hyaline cartilage.

11.
● An example of a synchondrosis is the epiphyseal (growth) plate that connects
the epiphysis and diaphysis of a growing bone.
● A photomicrograph of the epiphyseal plate. Functionally, a synchondrosis is a
synarthrosis.
● When bone elongation ceases, bone replaces the hyaline cartilage, and the
synchondrosis becomes a synostosis, a bony joint.
● Another example of a synchondrosis is the joint between the first rib and the
manubrium of the sternum, which also ossifies during adult life and becomes
an immovable synostosis, or bony joint.

12.
❖ Symphyses
● A symphysis is a cartilaginous joint in which the ends of the
articulating bones are covered with hyaline cartilage, but a
broad, flat disc of fibrocartilage connects the bones.
● All symphyses occur in the midline of the body.
● The pubic symphysis between the anterior surfaces of the hip
bones is one example of a symphysis.
● This type of joint is also found at the junction of the manubrium
and body of the sternum and at the intervertebral joints between
the bodies of vertebrae.
● A portion of the intervertebral disc is composed of fibrocartilage.
● A symphysis is an amphiarthrosis, a slightly movable joint.

13.
3. SYNOVIAL JOINTS

14.
Structure of Synovial Joints
● Synovial joints have certain characteristics that distinguish them from
other joints.
● The unique characteristic of a synovial joint is the presence of a
space called a synovial cavity between the articulating bones.
● Because the synovial cavity allows a joint to be freely movable, all
synovial joints are classified functionally as diarthroses.
● The bones at a synovial joint are covered by a layer of hyaline
cartilage called articular cartilage.
● The cartilage covers the articulating surface of the bones with a
smooth, slippery surface but does not bind them together.
● Articular cartilage reduces friction between bones in the joint during
movement and helps to absorb shock.

15.
Articular Capsule
● A sleeve like articular capsule surrounds a synovial joint,
encloses the synovial cavity, and unites the articulating bones.
● The articular capsule is composed of two layers, an outer
fibrous membrane and an inner synovial membrane.
● The fibrous membrane usually consists of dense irregular
connective tissue that attaches to the periosteum of the
articulating bones.
● In fact, the fibrous membrane is literally a thickened
continuation of the periosteum between the bones.
● The flexibility of the fibrous membrane permits considerable
movement at a joint, while its great tensile strength helps
prevent the bones from dislocating.

16.
● The fibers of some fibrous membranes are arranged as parallel bundles of
dense regular connective tissue that are highly adapted for resisting strains.
● The strength of these fiber bundles, called ligaments, is one of the principal
mechanical factors that hold bones close together in a synovial joint.
● The inner layer of the articular capsule, the synovial membrane, is composed
of areolar connective tissue with elastic fibers.

17.
● At many synovial joints the synovial membrane includes
accumulations of adipose tissue, called articular fat pads.
● An example is the infrapatellar fat pad in the knee.
● A “double-jointed” person does not really have extra joints.
● Individuals who are “double-jointed” have greater flexibility in their
articular capsules and ligaments; the resulting increase in range of
motion allows them to entertain fellow partygoers with activities
such as touching their thumbs to their wrists and putting their
ankles or elbows behind their necks.
● Unfortunately, such flexible joints are less structurally stable and
are more easily dislocated.

18.
Synovial Fluid
● The synovial membrane secretes synovial fluid, a viscous, clear or
pale yellow fluid named for its similarity in appearance and
consistency to uncooked egg white.
● Synovial fluid consists of hyaluronic acid secreted by fibroblast-like
cells in the synovial membrane and interstitial fluid filtered from
blood plasma.
● It forms a thin film over the surfaces within the articular capsule.
● Its functions include reducing friction by lubricating the joint,
absorbing shocks, and supplying oxygen and nutrients to and
removing carbon dioxide and metabolic wastes from the
chondrocytes within articular cartilage.

19.
● Synovial fluid also contains phagocytic cells that remove microbes and the
debris that results from normal wear and tear in the joint.
● When a synovial joint is immobile for a time, the fluid becomes quite viscous,
but as joint movement increases, the fluid becomes less viscous.
● One of the benefits of warming up before exercise is that it stimulates the
production and secretion of synovial fluid; more fluid means less stress on the
joints during exercise.

20.
● We are all familiar with the cracking sounds heard as certain joints move, or
the popping sounds that arise when people crack their knuckles.
● According to one theory, when the synovial cavity expands, the pressure of
the synovial fluid decreases, creating a partial vacuum.
● The suction draws carbon dioxide and oxygen out of blood vessels in the
synovial membrane, forming bubbles in the fluid.
● When the bubbles burst, as when the fingers are flexed (bent), the cracking or
popping sound is heard.

21.
Accessory Ligaments and Articular Discs
● Many synovial joints also contain accessory ligaments called
extracapsular ligaments and intracapsular ligaments.
● Extracapsular ligaments lie outside the articular capsule.
● Examples are the fibular and tibial collateral ligaments of the knee
joint.
● Intracapsular ligaments occur within the articular capsule but are
excluded from the synovial cavity by folds of the synovial membrane.
● Examples are the anterior and posterior cruciate ligaments of the
knee joint.
● Inside some synovial joints, such as the knee, pads of fibrocartilage
lie between the articular surfaces of the bones and are attached to
the fibrous capsule.

22.
● These pads are called articular discs or menisci.
● The discs usually subdivide the synovial cavity into two spaces, allowing
separate movements to occur in each space.
● As you will see later, separate movements also occur in the respective
compartments of the temporomandibular joint.
● By modifying the shape of the joint surfaces of the articulating bones,
articular discs allow two bones of different shapes to fit together more tightly.
● Articular discs also help to maintain the stability of the joint and direct the flow
of synovial fluid to the areas of greatest friction.

23.
TYPES OF SYNOVIAL JOINTS
● Although all synovial joints are similar in structure, the shapes of the
articulating surfaces vary; thus, many types of movements are possible.
● Synovial joints are divided into six categories based on type of movement:
▪ Planar, hinge,
▪ Pivot,
▪ Condyloid,
▪ Saddle, and
▪ Ball-and-socket.

24.
Planar Joints
● The articulating surfaces of bones in a planar joint are flat or slightly curved.
● Planar joints primarily permit back-and-forth and side-to-side movements
between the flat surfaces of bones.
● Many planar joints are biaxial because they permit movement around two
axes.
● An axis is a straight line around which a rotating (revolving) bone moves.

25.
● Examples of planar joints are
● the intercarpal joints (between carpal bones at the wrist),
● intertarsal joints (between tarsal bones at the ankle),
● sternoclavicular joints (between the manubrium of the sternum and the
clavicle),
● acromioclavicular joints (between the acromion of the scapula and the
clavicle),
● sternocostal joints (between the sternum and ends of the costal cartilages at
the tips of the second through seventh pairs of ribs),
● vertebrocostal joints (between the heads and tubercles of ribs and transverse
processes of thoracic vertebrae).

26.
Hinge Joints
● In a hinge joint, the convex surface of one bone fits into the
concave surface of another bone.
● As the name implies, hinge joints produce an angular, opening-
and-closing motion like that of a hinged door.
● In most joint movements, one bone remains in a fixed position
while the other moves around an axis.
●
● Hinge joints are monaxial because they typically allow motion
around a single axis.
● Hinge joints permit only flexion and extension.
● Examples of hinge joints are the knee, elbow, ankle, and
interphalangeal joints.

27.
Pivot Joints
● In a pivot joint, the rounded or pointed surface of one bone articulates with a
ring formed partly by another bone and partly by a ligament.
● A pivot joint is monaxial because it allows rotation only around its own
longitudinal axis.
● Examples of pivot joints are the atlanto-axial joint, in which the atlas rotates
around the axis and permits the head to turn from side to side as when you
shake your head “no”, and the radioulnar joints that enable the palms to turn
anteriorly and posteriorly.

28.
Condyloid Joints
● In a condyloid joint or ellipsoidal joint, the convex oval-shaped projection of
one bone fits into the oval-shaped depression of another bone.
● A condyloid joint is biaxial because the movement it permits is around two
axes.
● Examples of condyloid joints are the wrist and metacarpophalangeal joints
for the second through fifth digits.

29.
Saddle Joints
● In a saddle joint, the articular surface of one bone is saddle shaped, and the
articular surface of the other bone fits into the “saddle” as a sitting rider would
sit.
● A saddle joint is a modified condyloid joint in which the movement is
somewhat freer.
● Saddle joints are triaxial, permitting movements around three axes.
● An example of a saddle joint is the carpometacarpal joint between the
trapezium of the carpus and metacarpal of the thumb.

30.
Ball-and-Socket Joints
● A ball-and-socket joint consists of the ball-like surface of one bone
fitting into a cuplike depression of another bone.
● Such joints are triaxial, permitting movements around three axes.
● Examples of ball-and-socket joints are the shoulder and hip joints.
● At the shoulder joint, the head of the humerus fits into the glenoid
cavity of the scapula.
● At the hip joint, the head of the femur fits into the acetabulum of the
hip bone.

31.
TYPES OF MOVEMENTS AT SYNOVIAL JOINTS
● Anatomists, physical therapists, and kinesiologists use specific terminology to
designate the movements that can occur at synovial joints.
● These precise terms may indicate the form of motion, the direction of
movement, or the relationship of one body part to another during movement.
● Movements at synovial joints are grouped into four main categories:
(1) Gliding,
(2) Angular movements,
(3) Rotation, and
(4) Special movements.

32.
(1) Gliding
● Gliding is a simple movement in which relatively flat bone surfaces move
back-and-forth and from side-to-side with respect to one another.
● There is no significant alteration of the angle between the bones.
● Gliding movements are limited in range due to the structure of the articular
capsule and associated ligaments and bones.
● The intercarpal and intertarsal joints are examples of articulations where
gliding movements occur.

33.
(2) Angular Movements
● In angular movements, there is an increase or a decrease in the angle
between articulating bones.
● The major angular movements are flexion, extension, lateral flexion,
hyperextension, abduction, adduction, and circumduction.
● These movements are discussed with respect to the body in the anatomical
position.

34.
Flexion, Extension, Lateral Flexion, and
Hyperextension
● Flexion and extension are opposite movements.
● In flexion there is a decrease in the angle between articulating bones;
● in extension there is an increase in the angle between articulating bones,
often to restore a part of the body to the anatomical position after it has been
flexed.
● Both movements usually occur along the sagittal plane.

35.
● All of the following are examples of flexion (as you have probably already
guessed, extension is simply the reverse of these movements):
● Bending the head toward the chest at the atlanto-occipital
joint between the atlas (the first vertebra) and the occipital
bone of the skull, and at the cervical intervertebral joints
between the cervical vertebrae (Figure 9.5a)
● Bending the trunk forward at the intervertebral joints
● Moving the humerus forward at the shoulder joint, as in
swinging the arms forward while walking

36.
○ Moving the forearm toward the arm at the elbow joint
between the humerus, ulna, and radius
○ Moving the palm toward the forearm at the wrist or
radiocarpal joint between the radius and carpals
○ Bending the digits of the hand or feet at the
interphalangeal joints between phalanges
○ Moving the femur forward at the hip joint between the
femur and hip bone, as in walking

37.
� Moving the leg toward the thigh at the tibiofemoral joint
between the tibia, femur, and patella, as occurs when
bending the knee (Figure 9.5f) Although flexion and
extension usually occur along the sagittal plane, there are
a few exceptions.
� For example, flexion of the thumb involves movement of
the thumb medially across the palm at the
carpometacarpal joint between the trapezium and
metacarpal of the thumb, as when you touch your thumb
to the opposite side of your palm.

38.
● Another example is movement of the trunk sideways to the right or left at
the waist.
● This movement, which occurs along the frontal plane and involves the
intervertebral joints, is called lateral flexion.
● Continuation of extension beyond the anatomical position is called
hyperextension.

39.
● Examples of hyperextension include:
○ Bending the head backward at the atlanto-occipital and
cervical intervertebral joints
○ Bending the trunk backward at the intervertebral joints
○ Moving the humerus backward at the shoulder joint, as
in swinging the arms backward while walking
○ Moving the palm backward at the wrist joint (Figure
9.5d) Moving the femur backward at the hip joint, as in
walking Hyperextension of hinge joints, such as the
elbow, interphalangeal, and knee joints, is usually
prevented by the arrangement of ligaments and the
anatomical alignment of the bones.

40.
Abduction, Adduction, and Circumduction
● Abduction is the movement of a bone away from the midline; adduction is
the movement of a bone toward the midline.
● Both movements usually occur along the frontal plane.
● Examples of abduction include moving the humerus laterally at the shoulder
joint, moving the palm laterally at the wrist joint, and moving the femur
laterally at the hip joint.
● The movement that returns each of these body parts to the anatomical
position is adduction.

41.
● The midline of the body is not used as a point of reference for abduction and
adduction of the digits.
● In abduction of the fingers, an imaginary line is drawn through the longitudinal
axis of the middle (longest) finger, and the fingers move away (spread out)
from the middle finger.
● In abduction of the thumb, the thumb moves away from the palm in the
sagittal plane.
● Abduction of the toes is relative to an imaginary line drawn through the
second toe.
● Adduction of the fingers and toes returns them to the anatomical position.

42.
● Adduction of the thumb moves the thumb toward the palm in the sagittal
plane.
● Circumduction is movement of the distal end of a body part in a circle.
● Circumduction is not an isolated movement by itself but rather a continuous
sequence of flexion, abduction, extension, and adduction.
● Therefore, circumduction does not occur along a separate axis or plane of
movement.

43.
● Examples of circumduction are moving the humerus in a circle at the
shoulder joint, moving the hand in a circle at the wrist joint, moving the
thumb in a circle at the carpometacarpal joint, moving the fingers in a circle
at the metacarpophalangeal joints (between the metacarpals and
phalanges), and moving the femur in a circle at the hip joint.
● Both the shoulder and hip joints permit circumduction.
● Flexion, abduction, extension, and adduction are more limited in the hip
joints than in the shoulder joints due to the tension on certain ligaments and
muscles and the depth of the acetabulum in the hip joint.

44.
(3) Rotation
● In rotation, a bone revolves around its own longitudinal axis.
● One example is turning the head from side to side at the
atlanto-axial joint (between the atlas and axis), as when you
shake your head “no”.
● Another is turning the trunk from side to side at the
intervertebral joints while keeping the hips and lower limbs in
the anatomical position.
● In the limbs, rotation is defined relative to the midline, and
specific qualifying terms are used.
● If the anterior surface of a bone of the limb is turned toward the
midline, the movement is called medial (internal) rotation.

45.
● You can medially rotate the humerus at the shoulder joint as
follows: Starting in the anatomical position, flex your elbow and then
move your palm across the chest.
● You can medially rotate the femur at the hip joint as follows: Lie on
your back, bend your knee, and then move your leg and foot
laterally from the midline.
● Although you are moving your leg and foot laterally, the femur is
rotating medially.
● Medial rotation of the leg at the knee joint can be produced by
sitting on a chair, bending your knee, raising your lower limb off the
floor, and turning your toes medially.
● If the anterior surface of the bone of a limb is turned away from the
midline, the movement is called lateral (external) rotation.

46.
(4) Special Movements
● Special movements occur only at certain joints.
● They include
▪ Elevation,
▪ Depression,
▪ Protraction,
▪ Retraction,
▪ Inversion,
▪ Eversion,
▪ Dorsiflexion,
▪ Plantar flexion,
▪ Supination,
▪ Pronation,
▪ Opposition

47.
● Elevation is an upward movement of a part of the body, such as closing the
mouth at the temporomandibular joint to elevate the mandible or shrugging
the shoulders at the acromioclavicular joint to elevate the scapula.
● Its opposing movement is depression.
● Other bones that may be elevated include the hyoid, clavicle, and ribs.

48.
● Depression is a downward movement of a part of the body, such as opening
the mouth to depress the mandible or returning shrugged shoulders to the
anatomical position to depress the scapula.

49.
● Protraction is a movement of a part of the body anteriorly in the transverse
plane.
● Its opposing movement is retraction.
● You can protract your mandible at the temporomandibular joint by thrusting
it outward or protract your clavicles at the acromioclavicular and
sternoclavicular joints by crossing your arms.
● Retraction is a movement of a protracted part of the body back to the
anatomical position.

50.
● Inversion is movement of the sole medially at the intertarsal joints.
● Its opposing movement is eversion.
● Physical therapists also refer to inversion of the feet as supination.
● Eversion is a movement of the sole laterally at the intertarsal joints.
● Physical therapists also refer to eversion of the feet as pronation.

51.
● Dorsiflexion refers to bending of the foot at the ankle or talocrural joint
(between the tibia, fibula, and talus) in the direction of the dorsum.
● Dorsiflexion occurs when you stand on your heels.
● Its opposing movement is plantar flexion.
● Plantar flexion involves bending of the foot at the ankle joint in the direction
of the plantar or inferior surface, as when you elevate your body by standing
on your toes.

52.
● Supination is a movement of the forearm at the proximal and distal
radioulnar joints in which the palm is turned anteriorly.
● This position of the palms is one of the defining features of the anatomical
position.
● Its opposing movement is pronation.
● Pronation is a movement of the forearm at the proximal and distal radioulnar
joints in which the distal end of the radius crosses over the distal end of the
ulna and the palm is turned posteriorly.

53.
● Opposition is the movement of the thumb at the carpometacarpal joint
(between the trapezium and metacarpal of the thumb) in which the thumb
moves across the palm to touch the tips of the fingers on the same hand.
● This is the distinctive digital movement that gives humans and other
primates the ability to grasp and manipulate objects very precisely.

54.
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YOU