Skeletal System – Part 8
Joints
 Every bone in the body
(except the hyoid bone of
the neck) forms a joint
with at least one other
bone.
 Joints (Articulations)
– Sites where two or more
bones meet.
Functions of Joints
 Joints have two functions:
1. Hold the bones together securely
2. Give the rigid skeleton mobility
 Joints are classified in two ways:
1. Functionally (focuses on the amount of
movement allowed by the joint)
2. Structurally
Functional Classification of Joints
1. Synarthroses: Immoveable joints; Allows
no movement.
- Example: Bones in the skull
2. Amphiarthroses – Slightly moveable
joints; Allow a small amount of
restricted movement.
- Example: Vertebrae and the joints
between the two bones of the lower leg.
3. Diarthroses - Freely Moveable; Permit
movement in one or more directions
- Example: Shoulder, neck, and knee
Structural Classification of Joints
 Structurally,
there are three
types of joints:
1.
2.
3.
Fibrous
Joints
Cartilagenous
Joints
Synovial
Joints
Fibrous Joints
 Fibrous Joints – The
bones are united by fibrous
tissue; As a general rule,
these are immoveable.
 Bones
are bound tightly
together by CT fibers, allowing
essentially no movement.
Example: Sutures of the
skull.
Cartilagenous Joints
 Cartilagenous
Joints – Bone ends
are connected by
cartilage.
Cartilagenous Joints
 Slightly Moveable
Examples:



Pubic symphysis of the pelvis
Intervertebral joints of the spinal
column (connected by discs of
fibrocartilage)
Most cartilagenous joints are
slightly moveable
 Immoveable Examples:


The Epiphyseal plates of growing
long bones
Joints between the first ribs and
the sternum.
Synovial Joints
 Synovial Joints – Joints in
which the articulating bone ends
are separated by a joint cavity
containing synovial fluid.
All synovial joints have four distinguishing
characteristics:
1. Articular cartilage

Covers the ends of the bones
forming the joint.
2. Fibrous articular
capsule
Joint surfaces are enclosed
by a sleeve or capsule of
fibrous CT
 The capsule is lined with a
smooth synovial membrane
(the reason these joints are
called synovial joints).

All synovial joints have four distinguishing
characteristics (continued):
3. Joint cavity

The articular capsule
encloses a cavity, called the
joint cavity, which contains
lubricating synovial fluid.
4. Reinforcing ligaments

The fibrous capsule is
usually reinforced with
ligaments.
Bursae
 Bursae are often found
closely associated with
synovial joints.
 Bursae
– Flattened
fibrous sacs lined with
synovial membrane and
containing a thin film of
synovial fluid.
 Common
where ligaments,
muscles, skin, tendons, or
bones rub together.
Tendon Sheaths
 Tendon sheaths are often found closely
associated with synovial joints.
 Tendon
Sheath – An elongated bursae that
wraps completely
around a tendon
subjected to
friction.
 Like
a bun around
a hot dog.
Types of Synovial Joints: Based on Shape
1. Plane
2. Hinge
3. Pivot
4. Condyloid
5. Saddle
6. Ball-and-
socket
Plane Joint
 Plane Joint – The articular
surfaces are essentially flat,
and only short slipping or
gliding movements are
allowed.
 Movements
are nonaxial (does
not involve rotation around
any axis).
 Examples: Intercarpal joints
of the wrist.
Hinge Joint
 Hinge Joint – The
cylindrical end of one bone
fits into a trough-shaped
surface on another bone.

Angular movement is allowed in
just one plane, like a mechanical
hinge.
 Classified
as uniaxial (they allow
movement around one axis only).

Examples: elbow joint, ankle
joint, and the joints between the
phalanges of the fingers.
Pivot Joint
 Pivot Joint – The
rounded end of one bone
fits into a sleeve or ring of
bone.
Because the rotating bone
can turn only around its long
axis, pivot joints are also
uniaxial joints.
 Examples:

 Proximal
radioulnar joint
 Joint between the atlas and
the dens of the axis
Condyloid Joint
 Condyloid Joint – The
egg-shaped articular surface
of one bone fits into an oval
concavity in another.
Both of these articular surfaces
are oval.
 Allow the moving joint to travel
(1) from side to side and (2)
back and forth.

 But
the bone cannot rotate
around its long axis.
 Movement occurs around two
axes, hence these joints are
biaxial.
Saddle Joint
 Saddle Joint – Each
articular surface has both
convex and concave areas,
like a saddle.
These biaxial joints allow
essentially the same
movements as condyloid
joints.
 Example: Carpometacarpal

joints in the thumbs
Ball-and-Socket Joint
Ball-and-Socket
Joint – The spherical
head of one bone fits
into a round socket in
another.



These multiaxial joints
allow movement in all
axes, including rotation
and are the most freely
moving synovial joints.
Examples: Shoulder and
hip
Dislocations
 A dislocation happens when
a bone is forced out of its
normal position in the joint
cavity.

Reduction – The process of
returning the bone to its proper
position.
Should be done only by a physician.
 Attempts by an untrained person to
“snap the bone back into its socket”
are usually more harmful than
helpful.

Sprains
 Sprains – The ligaments or tendons reinforcing a
joint are damaged by excessive stretching, or they are
torn away from the bone.

Since tendons and ligaments get poor blood supply, sprains
heal slowly and are extremely painful.