JOINTS
Chapter 8
Introduction


Joints or articulations are sites where two
or more bones meet
Joints have two fundamental functions:
– provide for skeletal mobility
– hold the skeleton together

Weakest parts of the skeleton, yet have a
remarkable ability to resist the forces
that tear them apart
Classification of Joints

Structural classification
– focuses on the material binding the bones
together and whether or not there is a joint
cavity (fibrous, cartilaginous, synovial)

Functional classification
– based on the amount of movement allowed
at the joint (synarthroses, amphiarthoroses,
diarthroses)
Functional Classification

Synarthroses
– Immovable joints

Amphiarthroses
– Slightly movable joints

Diarthroses
– Freely movable joints
Structural Classification

Fibrous
– Joined by fibrous tissue

Cartilaginous
– Joined by cartilage

Synovial
– The bones are joined and surrounded by a
joint cavity

Note:
– Structural classification is the system used in
your text
Summary of Joint Classes

Fibrous joints
– Suture
– Syndesmoses
– Gomphoses

Cartilaginous joints
– Synchondroses
– Symphyses

Synovial
– Gliding, hinge, pivot, condyloid, saddle, and
ball and socket
Fibrous Joints
In fibrous joints the bones are joined by
fibrous tissue; no joint is present. The
three types of fibrous joints are. . .
 Sutures
– Dense fibrous connective tissue

Syndesmosis
– A cord or band of connective tissue

Gomphosis
– Peg-in-socket arrangement surrounded by
fibrous tissue or peridontal ligament
Suture Joint




Occurs only
between bones of
the skull
Wavy articulating
bone edges
interlock
Junction is filled
by connective
tissue
Rigid splices bind
bones of the skull
together tightly
Syndesmosis



Longer fibrous
tissue occurs as a
sheet or
membrane
Longer fibrous
tissue permits
the joint to
“give” or flex
True movement
is not possible
Gomphosis



Fibrous tissue
holds teeth in
their sockets
Teeth
embedded in
sockets of bone
Anchored by
fibers of
periodontal
ligament
Cartilaginous Joints
In cartilaginous joints, the articulating
bones are united by cartilage, there is no
joint cavity
 Synchondrosis
– Hyaline cartilage unites the bones

Symphysis
– Fibrocartilage unites the bones
Synchondroses




Hyaline cartilage
unites the bones
Epiphyseal plates in
growing children
Provide for bone
growth
When growth ends
all synchondroses
become immovable
Epipyseal
Plate
Synchrondroses

Sternocostal
joint between
the manubrium
and rib 1 is a
immovable
hyaline
cartilage joint
Symphyses


Bone surfaces are
covered with
articular hyaline
cartilage which is
fused to a pad of
fibrocartilage
Fibrocartilage is
resilient and acts
as a shock
absorber and
permits limited
movement
Pubic Symphysis
Synovial Joints



In synovial joints articulating bones are
located within a fluid containing joint
cavity
Synovial joints permit substantial range
of motion
All synovial joints have similar features
Structures of Synovial Joint

Articular cartilage
– Hyaline cartilage on opposing bone surfaces

Joint (synovial) cavity
– Space filled with fluid

Articular capsule
– Capsule to confine fluid

Synovial fluid
– Fluid to lubricate joints

Reinforcing ligaments
– Maintain joint alignment
Articular Cartilage



Hyaline cartilage
covers the bone
surfaces
Cartilage
absorbs the
compression
placed on the
joint
Cartilage keeps
the bone ends
from being
crushed
Joint (synovial)
cavity


Joint spaces are
unique to
synovial joints
Joint spaces are
filled with
synovial fluid
Articular capsule



The joint cavity is
enclosed by a
double layered
articular capsule
The external layer
is a tough flexible
fibrous capsule
The inner synovial
membrane
Synovial Fluid



Synovial fluid fills
the entire joint
Slippery fluid
lubricates joint
Weeping
lubrication
squeezes synovial
fluid into and out
of the cartilage
nourishing the
cells
Synovial
Fluid
Reinforcing ligaments




Ligaments
reinforce joints
Intrinsic
ligaments
reinforce capsule
Extracapsular
are outside
capsule
Intracapsular are
inside capsule
Extracapsular
Ligament
Intracapsular
Ligament
Features of Select Synovial Joints

Certain synovial joints have additional
structural features
– Fatty pads cushion the knee and hip joints
– Fibrocartilage articular discs separates
articular surfaces (menisci)
– Articular discs improve the fit between the
articulating surfaces (knee, jaw)
Bursae and Tendon Sheaths




Bursae and tendon sheaths are closely
associated with synovial joints
Essentially sacs of lubricant
Function as “ball bearings” to reduce
friction between adjacent structures
Reduces friction during joint activity
Bursae


Bursae are
flattened fibrous
sacs lined with
synovial membrane
and containing a
thin film of synovial
fluid
Common at sites
where ligaments,
skin, muscles or
tendons rub against
a bone
Bursae: Anomolies



A bunion is an enlarged bursae at the
base of the big toe
False bursae may develop at any site
where there is excessive motion
Function similar to a true bursae
Tendon Sheaths



An elongated bursa
that wraps completely
around a tendon
subjected to friction
Tendon slides within
this lubricated sleeve
Common at sites
where the tendon is
subject to friction
from other tendons or
bone features
Tendon
Sheath
Retinaculum
Retinaculum



Retinaculum function to confine tendons to a
specific line of pull
Muscle exerts a force around a skeletal feature
Similar to a pulley or gear changing the angle of
force exerted by a machine
Factors Influencing Synovial
Joint Stability

The stability of a synovial joint depends
on three factors . . .
– The nature of the articular surfaces
– The number and positioning of the ligaments
– The tone and strength of the muscles acting
upon the joint
Articular Surfaces




The surfaces determine what movements
are possible at a joint, but play a minimal
role in joint stability
Many joints have shallow, “misfit”
surfaces
Larger surfaces or deeper sockets vastly
improve stability
Ball and socket joints are very stable
because of their articular surfaces
Articular Surfaces



The knee is a hinge joint
by classification
The knee is an example
of a joint that allows for
“extra” movements
The joint surfaces allow
for some anterior posterior sliding,
sliding, as well as a
slight amount of
rotation at full extension
Ligaments



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Ligaments unite the bones of a joint
Ligaments help to direct bone movement
and prevent excessive or undesirable
motion
As a rule, the more ligaments a joint has
the stronger it is
Ligaments can stretch due to undue
tension or trauma
Ligaments can stretch only 6% of its
length before it snaps
Supporting Ligaments


The supporting
ligaments of the
elbow allow
flexion / extension
and restrict
movement in any
other plane
The Annular
ligament allows
for rotation of the
head of the radius
but restricts other
movements
Muscle Tone




In most joints the muscles that act upon a
joint are the most important stabilizing factor
The tendons of the muscles keep the joint
taunt and provide dynamic support
Muscle tone is extremely important in
reinforcing the shoulder and knee joint as
well as the arches of the foot
The articular capsule and the ligament have
extensive sensory nerve endings providing
reflexive contraction of supporting muscles
Muscle Tone



The knee is a
joint that features
movement over
stability
The knee is very
dependent upon
the muscles to
provide dynamic
stability to the
joint while it
moves
Note: Rehab
Movements Allowed by
Synovial Joints



Nonaxial
Biaxial
Multiaxial
Gliding Movements



Simplest type of
joint movement
Bone surface
glides or slips
over another
similar surface
Occur at the
intercarpal and
intertarsal
joints as well as
articular
processes of
vertebrae
Flexion/Extension

Flexion
– A bending
movement
that decreases
the angle of
the joint

Extension
– A movement
that increases
the angle of
the joint
Flexion/Extension/Hyperextension

Flexion
– A bending movement
that decreases the angle
of the joint

Extension
– A movement that
increases the angle of the
joint

Hyperextension
– Bending beyond the
upright position
Flexion

Flexion
– A bending movement
that decreases the angle
of the joint and brings
the two articulating
bones closer together
– Movement usually occurs
in the sagittal plane

Illustrated
– Flexion of the arm
– Flexion of the leg
Extension

Extension
– A movement
that increases the
angle of the joint
that moves the
two articulating
bones farther
apart
– Movement
within the
sagittal plane

Illustrated
– Extension of the
leg and arm
Dorsiflexion and Plantar Flexion

Dorsiflexion
– Lifting the
foot so that its
superior
surface nears
the shin

Plantar flexion
– Depressing
the foot or
pointing the
toes
downward
Ab/Adduction/Circumduction

Abduction
– Movement of a limb away
from midline or a
spreading of the digits of
the hand or foot

Adduction
– Movement of a limb
toward midline or in the
case of the digits toward
the midline of the hand or
foot

Circumduction
– Movement of a limb in a
circle
Rotation

Rotation is the turning
of a bone around its
own long axis
– Only movement possible
between C1 & C2
– Common at the hip and
shoulder joints
– Medial or lateral is a
function of whether
rotation results in the
anterior surface of the
limb moving toward or
away from the midline of
the body
Supination and Pronation
Inversion and Eversion
Protraction and Retraction
Elevation and Depression
Opposition
Types of Synovial Joints


Although all synovial joints have the
same features they do not have a common
structural plan
Based on the shape of their articular
surfaces there are six major categories of
synovial joints
– Plane, hinge, pivot, condyloid, saddle, and
ball and socket
Plane Joint



A plane joint is the
only example of a
nonaxial joint
Articular surfaces
are essentially flat
Allow only short
slipping or gliding
movements
Plane Joints


No rotation
around an axis
Examples
– Intercarpals
– Intertarsals
– Vertebrae
Plane
joints
Hinge Joints



In hinge joints a
cylindrical shaped
projection of bone
fits into a trough
shaped surface of
another bone
Motion is within a
single plane
Joint components
resemble that of a
mechanical hinge
Hinge Joints



The elbow joint is
an example of a
hinge joint
It allows for
movement (flexion
and extension) in
only one plane
Other example
– Knee
Pivot Joints


The rounded end of
a bone protrudes
into a ring of bone
and ligaments on
another bone
Only movement
allowed is rotation
of bone around long
axis
Pivot Joints


An example is the
joint between the
atlas and axis,
which allows your
head to move side to
side
Another example is
the proximal
radioulnar joint,
where the head of
the radius rotates
within the annular
ligment
Condyloid Joints


In condyloid joints
the oval articular
surface of one bone
fits into a complementary concavity
in another
Both articulating
surfaces are oval
shaped
Condyloid Joints

The biaxial joints
permits all angular
motions
– flexion / extension
– abduction
adduction
– Circumduction

Metacarpophalangeal joints
Saddle Joints



Resemble condyloid
joints, but allow
greater freedom of
movement
Each surface has
both a concave and
a convex surface
that fit together
Each surface is
shaped like a saddle
Saddle Joints

The best example of
a saddle joint in the
body are the carpometacarpal joints of
the thumb
Saddle
Joint
Ball and Socket Joint


The spherical head
of one bone
articulates with the
cuplike socket of
another
These joints are
multiaxial and the
most freely moving
synovial joints
Ball and Socket Joints



Movements in all
planes is allowed
All axis and planes
Examples
– Shoulder
– Hip
Head of
Femur fits
Acetabulum
Of pelvis
Shoulder (Glenohumeral) Joint

The shoulder
joint has
sacrificed
stability for
mobility
Shoulder (Glenohumeral) Joint


The glenoid
labrum deepens
the cavity
The articular
capsule is thin
and loose to
contribute to
movement
Shoulder (Glenohumeral) Joint

Ligaments
reinforce
primarily the
anterior aspect
– Coracohumeral
– Glenohumeral
– Transverse
humeral
Shoulder (Glenohumeral) Joint


Muscles
crossing the
joint provide
most of the
stability
Long head of
the biceps is
the most
important
stabilizer
Shoulder (Glenohumeral) Joint

Four tendons
of the rotator
cuff encircle
the joint,
blend with the
capsule
–
–
–
–
Subscapularis
Supraspinatus
Infraspinatus
Teres minor
Shoulder Joint


The joint lacks structural stability and
shoulder dislocations are quire common
Since the shoulder is weakest anteriorly
and inferiorly, the humerous tends to
dislocate forward and downward
Hip Joint



This ball and socket
joint has good range
of motion but the
motion is limited by
the deep socket and
the joint ligaments
Deep acetabulum is
enhanced by circular
acetabular labrum
Ligamentum teres
provides internal
support to the joint
Hip Joint



This ball and socket
joint has good range
of motion but the
motion is limited by
the deep socket and
the joint ligaments
Deep acetabulum is
enhanced by circular
acetabular labrum
Ligamentum teres
provides internal to
the joint
Hip Joint


Thick articular capsule encloses the joint
Several strong ligaments support the joint
– Iliofemoral, Pubofemoral, Ischiofemoral

Ligaments are arranged in such a manner that
they screw the head of the femur into the
acetabulum when standing erect
Elbow Joint



The ulna and humerus provide a stable hinge
joint that allow flexion and extension
The Annular ligament anchors the head of the
radius
Supported laterally and medially by ligaments
Knee Joint




Largest and most
complex joint
Allows for flexion
extension and
some rotation
C-shaped menisci
deepen the tibial
articular surface
Menisci prevent
side to side
rocking and act a
shock absorbers
Knee Joint



The intracapsular
ligaments of the
knee cruciates are
located within the
intercondylar notch
Ligaments restrict
anterior / posterior
displacement
Ligaments are
named for their
tibial attachment
sites
Knee Joint


Posteriorly the
joint is reinforced
by the oblique
popliteal ligament
Gastrocnemius has
two head that
cross the joint
posteriorly and
provide dynamic
stability
Analysis of Knee Movements



Weight bearing begins with
the femur sliding
posteriorly on the posterior
aspect of the condyles
During extension the
femoral condyles travel
forward until restricted by
the anterior cruciate
ligament
Finally the lateral condyle
stops before the medial
spinning the joint into a
locked position
Analysis of Knee Movements

When extending the
knee as in kicking the
same movements
occur but in this case
the tibia does the
moving
Analysis of Knee Injuries


Knee is vulnerable
to horizontal forces
or high tension
twisting movements
These factors lead to
– Isolated meniscus
tears
– Isolated medial
collateral ligament
tears
– Isolated cruciate
tears
– Triad of O’Donahue
Orthopedic Injuries to Joints





Sprains - Ligament supporting a joint
are stretched or torn
Strains - Tendons or muscle fibers are
stretched or torn
Cartilage - Tear or fragmentation of the
cartilaginous tissue
Dislocation - Bones are forced out of their
normal alignments at a joint
Bursitis/Tendonitis - Inflammation
caused by trauma or more frequently
overuse
Degenerative Conditions of Joints

Arthritis
– A general reference to over 100 different
types of inflammatory or degenerative
diseases of the joints

Osteoarthritis
– A degenerative disease related to the aging
process (wear-and-tear arthritis)

Rheumatoid Arthritis
– A chronic inflammatory disorder alters the
synovival membrane
– Can lead to changes in articular cartilage
and bone tissue of the joints
Degenerative Conditions of Joints

Gouty Arthritis
– Abnormal amount of Uric acid contribute to
the deposition of urate crystals in the soft
tissues of joints
– Lead to agonizingly painful joints
– If untreated can lead to fusion and
immobilization of the joint
End of Chapter
Chapter 8