JOINTS
Joints
• Joints or articulations: sites where two
or more bones meet
– Gives our skeleton mobility and holds it
together
– Weakest parts of the skeleton:
• Yet, their structure resists various forces, such
as crushing or tearing, that threaten to force
them out of alignment
Structural Classification
• Focuses on the material binding the bones
together and whether or not a joint cavity is
present
– In fibrous joints the bones are joined together by
fibrous tissue and lack a joint cavity
– In cartilaginous joints the bones are joined
together by cartilage and they lack a joint cavity
– In synovial joints, the articulating bones are
separated by a fluid-containing joint cavity
Functional Classification
• Is based on the amount of movement
allowed at the joint:
– Synarthroses are immovable joints
– Amphiarthroses are slightly movable joints
– Diarthroses are freely movable joints
Fibrous Joints
• Bones joined by fibrous tissue
• No joint cavity
• Amount of movement allowed depends on
the length of the connective tissue fibers
uniting the bones
– A few are slightly movable, most are immovable
• Three types:
– Sutures
– Syndesmoses
– Gomphoses
Fibrous Joints
Sutures
•
•
Occur only between bones of
the skull
Wavy articulating bone edges
interlock, and the junction is
completely filled by a minimal
amount of very short
connective tissue fibers that are
continuous with the periosteum
– During middle age, the fibrous
tissue ossifies and the skull
bones fuse into a single unit
• At this stage, the sutures are
more precisely called
synostoses (bony junctions)
• Because movement of the
cranial bones would damage
the brain, the immovable nature
of sutures is a protective
adaptation
FIBROUS JOINT
Fibrous Joints
Syndesmoses
• Bones are connected by a ligament
(cord or band of fibrous tissue)
– Connecting fibers vary in length: amount
of movement allowed depends on the
length of the connecting fibers
Fibrous Joints
Syndesmoses
• Slight to considerable
movement is possible
– Examples:
– 1. Ligament connecting the
distal ends of the tibia and
fibula is short, and this joint
allows only slight movement
• True movement is still
prevented, so the joint is
classed functionally as an
immovable joint, or
synarthrosis (amphiarthrosis)
– 2. Ligament (interosseous
membrane) connecting the
radius and ulna along their
length are long enough to
permit rotation of the radius
around the ulna
FIBROUS JOINT
Fibrous Joints
Syndesmoses
Fibrous Joints
Gomphoses
• Gompho: Greek for
nail/bolt
• Peg-in-socket fibrous
joint
– Refers to the way teeth are
embedded in their sockets
(as if hammered in)
• Only example is the
articulation of a tooth
with its bony alveolar
socket
– Fibrous connection is the
short periodontal
ligament
Fibrous Joints
Gomphoses
Cartilaginous Joints
• Articulating joints are united by cartilage
• Lack joint cavity
• Two types:
– Synchondroses
– Symphyses
Cartilaginous Joints
Synchondroses
•
•
•
A bar or plate of hyaline cartilage unites the bones at a synchondrosis (junction of
cartilage)
Virtually all synchondroses are synarthrotic (immovable)
Examples:
– Epiphyseal plates connecting diaphysis and epiphysis regions in long bones of children
• (a):Epiphyseal plates are temporary joints and eventually become synostoses (bony
junctions)
– (b):Immovable joint between the costal cartilage of the first rib and the manubrium of the
sternum
Cartilaginous Joints
Symphyses
Cartilaginous Joints
Symphyses
•
•
Symphyses (growing together)
Articular surfaces of the bones are covered with articular (hyaline) cartilage,
which in turn is fused to an intervening pad, or plate, of fibrocartilage
–
•
Since fibrocartilage is compressible and resilient, it acts as a shock absorber and
permits a limited amount of movement at the joint
Amphiarthrotic joints (synarthrosis: immovable) designed for strength with
flexiblity:
–
Examples:
•
•
Intervertebral joints
Pubic symphysis of the pelvis
Cartilaginous Joints
Symphyses
Cartilaginous Joints
Symphyses
Synovial Joints
• Articulating bones are separated by a
fluid-containing joint cavity
– This arrangement permits substantial
freedom of movement, and all synovial
joints are freely movable diarthroses
(freely movable)
• All joints of the limbs—indeed, most
joints of the body—fall into this class
SYNOVIAL JOINT
Synovial Joints
General Structure
• Contains five
distinguishing features
• 1.Glassy-smooth
articular (hyaline)
cartilage covers the
ends of the opposing
articulating bones
– Thin but spongy cushions
absorb compression placed
on the joint and thereby
keep the bone ends from
being crushed
• 2.The joint (synovial)
cavity is a space that is
filled with synovial fluid
SYNOVIAL JOINT
Synovial Joints
General Structure
– 3.The two-layered articular
capsule encloses the joint
cavity
• The external layer is a
tough fibrous capsule,
composed of dense
irregular connective tissue,
that is continuous with the
periostea of the articulating
bones
– It strengthens the joint so
that the bones are not
pulled apart
• The inner layer of the joint
capsule is a synovial
membrane composed of
loose connective tissue
– Besides lining the fibrous
capsule internally, it
covers all internal joint
surfaces that are not
hyaline cartilage
SYNOVIAL JOINT
Synovial Joints
General Structure
• 4.Synovial (joint egg) fluid is
a viscous egg-white
consistency, slippery fluid
that fills all free space within
the joint cavity
– Derived largely by filtration
from blood flowing through
the capillaries in the
synovial membrane
– Viscous egg-white
consistency due to its
content of hyaluronic acid
secreted by cells in the
synovial membrane, but
thins, becoming less
viscous, as it warms during
joint activity
SYNOVIAL JOINT
Synovial Joints
General Structure
• 4.Synovial fluid:
– Also found within the
articular cartilage providing
a slippery weight-bearing
film that reduces friction
between the cartilages
• Forced from the cartilage
when a joint is compressed:
weeping lubrication
(lubricates the free
surfaces of the cartilages
and nourishes their cells)
– Seeps back into the
articular cartilages like
water into a sponge, ready
to be squeezed out again
the next time the joint is
put under pressure
– Contains phagocytic cells
that rid the joint cavity of
microbes and cellular debris
SYNOVIAL JOINT
Synovial Joints
General Structure
•
5.Reinforcing ligaments cross
synovial joints to strengthen
the joint
– Capsular, or intrinsic ligaments:
thickened parts of the fibrous
capsule
– Extracapsular ligaments:
outside the capsule
– Intracapsular ligaments: deep to
the capsule
• Since they are covered with
synovial membrane, they do not
actually lie within the joint cavity
– Double jointed:
• People whose joint capsules
and ligaments are more
stretchy and looser than
average
• They have the same number of
joints
SYNOVIAL JOINT
Synovial Joints
General Structure
• Richly supplied with sensory nerve endings that
monitor joints position and help maintain muscle
tone
• Richly supplied with blood vessels, most of which
supply the synovial membrane
• Other specific structures:
– Hip, knee joints:
• Fatty pads between the fibrous capsule and the synovial
membrane or bone
– Knee, jaw, sternum and clavicle, shoulder, distal radioulnar:
• Wedge of fibrocartilage separating the articular surfaces
– Called articular dics, or menisci
– Extends inward from the articular capsule and partially or completely
divides the synovial cavity in two
– Improve the fit between articulating bone ends, making the joint
more stable and maintaining wear and tear on the joint surfaces
KNEE JOINT
KNEE JOINT
Bursae and Tendon Sheaths
•
•
•
Not strictly part of the synovial
joint, BUT often found closely
associated with the joint
Bags of lubricant that reduce
friction at synovial joints during
joint activity
Bursae (purse): 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
– Example:
• Bunion: enlarged bursa at the
base of the big toe, swollen
from rubbing of a tight or
poorly fitting shoe
Bursae and Tendon Sheaths
• Tendon sheath:
– Essentially an
elongated bursa that
wraps completely
around a tendon
subjected to friction
• Like a bun around a
hot dog
BURSAE
Factors Influencing the Stability of
Synovial Joints
• Because joints are constantly stretched and
compressed, they must be stabilized so that
they do not dislocate (come out of alignment)
• Stability of a synovial joint depends chiefly
on three factors:
– 1.The shapes of the articular surfaces of bones
found at a synovial joint :
• Determines the movements that occur at the joint
• Play a minimal role in stabilizing the joint
– Example: ball and deep socket of the hip joint provides the
best example of a joint made extremely stable by the shape
of its articular surfaces
Factors Influencing the Stability of
Synovial Joints
• 2.Number and positioning of ligaments:
– Ligament: band of regular fibrous tissue that connects
bones
– Capsules and ligaments of synovial joints unite the bones and
prevent excessive or undesirable motion
• As a rule: the more ligaments a joint has, the stronger it
is
– When other stabilizing factors are inadequate, undue tension
is placed on the ligaments and they stretch
• Stretched ligaments stay stretched (like taffy)
• A ligament can stretch only about 6% of its length before it
snaps
– When ligaments are the major means of bracing a
joint, the joint is not very stable
Factors Influencing the Stability of
Synovial Joints
• 3.Muscle tone: low levels of contractile
activity in relaxed muscles
– Keeps the muscles healthy and ready to react to
stimulation
– For most joints, the muscle tendons that cross the
joint are the most important stabilizing factor
• Tendon: cord of dense fibrous tissue attaching muscle
to bone
– Kept taut at all times by the tone of their muscles
– Extremely important in reinforcing the shoulder
and knee joints and the arches of the foot
Movements Allowed by Synovial Joints
• Every skeletal muscle of the body is attached to
bone or other connective tissue structures at no
fewer than two points
– The muscle’s origin is attached to the immovable (or less
movable) bone
– The other end, the insertion, is attached to the movable bone
• Body movement occurs when muscles contract across
joints and their insertion moves toward their origin
• Movements can be described in directional terms
relative to the lines, or axes, around which the body part
moves and the planes of space along which movement
occurs, that is, along the transverse, frontal, or sagittal
plane
Movements Allowed by Synovial Joints
• Range of motion:
– Nonaxial: slipping movements only
• No axis around which movement can occur
– Uniaxial:
• Movement in one plane
– Biaxial:
• Movement in two planes
– Multiaxial:
• Movement in or around all three planes of space
and axes
Movements Allowed by Synovial Joints
• Three general types of movement:
– 1. Gliding
– 2. Angular
– 3. Rotation
Movements Allowed by Synovial Joints
• In gliding movements:
– Also known as
translation
– One flat, or nearly flat,
bone surface glides or slips
over another (back-andforth or side-to-side)
without appreciable
angulation or rotation
– Examples:
• Intercarpal and intertarsal
joints
• Flat articular processes of
the vertebrae
Synovial Movement
Gliding
Movements Allowed by Synovial Joints
• Angular movements:
– Increase or decrease the angle between two
bones
– May occur in any plane of the body and include:
•
•
•
•
•
•
Flexion
Extension
Hyperextension
Abduction
Adduction
Circumduction
Movements Allowed by Synovial Joints
• Angular Flexion:
– Bending movement, usually along the sagittal
plane
– Decreases the angle of the joint and brings the
articulating bones closer together
– Examples:
• (b): Bending the knee from a straight to an angled position
• (b): Arm flexed at the shoulder when the arm is lifted in an
anterior direction
• (c): Bending the body trunk from a straight to an angled
position
• (d): Bending the head forward on the chest
Movements Allowed by Synovial Joints
• Angular Flexion:
– (b): Bending the knee from a straight to an angled
position
– (b): Arm flexed at the shoulder when the arm is lifted
in an anterior direction
SYNOVIAL MOVEMENT
Movements Allowed by Synovial Joints
• Angular Flexion:
– (c): Bending the body
trunk from a straight to
an angled position
• Lateral Flexion:
lateral bending of the
trunk away from the
body midline in the
frontal plane
Movements Allowed by Synovial Joints
Angular Flexion:
(d): Bending the head
forward on the chest
SYNOVIAL MOVEMENT
Movements Allowed by Synovial Joints
• Angular Extension:
– Reverse of flexion and occurs at the same
joints
– Involves movement along the sagittal
plane that increases the angle between the
articulating bones
– Examples:
• Straightening a flexed elbow or knee
• (c): straightening a flexed body trunk
• (d): straightening a flexed neck
Movements Allowed by Synovial Joints
• Angular Extension:
– (c): straightening a
flexed body trunk
• Angular
Hyperextension:
– Bending backward
beyond its straight
(upright) position
SYNOVIAL MOVEMENT
Movements Allowed by Synovial Joints
• Angular Extension:
– (d): straightening a
flexed neck
• Angular
Hyperextension:
– Bending backward
beyond its straight
(upright) position
SYNOVIAL MOVEMENT
Movements Allowed by Synovial Joints
•
Up-and-down movements of the
foot at the ankle joint are given
more specific names
– (e): Dorsiflexion:
• Lifting the foot so that its
superior surface approaches
the shin
• Decreases the angle between
the top of the foot (dorsal
surface) and the anterior
surface of the tibia
• Corresponds to wrist
extension
– (e): Plantar flexion:
• Depressing the foot
• Decreases the angle between
the sole of the foot (plantar
surface) and the posterior
side of the tibia
• Corresponds to wrist
flexion
SYNOVIAL MOVEMENT
Movements Allowed by Synovial Joints
• Angular Abduction (f):
– Moving away
– Movement of a limb (or
fingers) away from the midline
or median plane of the body
(or of the hand), along the
frontal plane
– Examples:
• Raising the arm laterally
• Raising the thigh laterally
• When the term is used to
indicate the movement of
the fingers or toes, it
means spreading them
apart
– In this case midline is the
longest digit (third finger
or second toe)
SYNOVIAL MOVEMENT
Movements Allowed by Synovial Joints
• Angular Adduction (f):
– Moving toward
– Opposite of abduction
– Movement of a limb (or
fingers) toward the midline
of the body (or the hand)
• In the case of digits,
toward the midline of the
hand or foot (In this case
midline is the longest
digit (third finger or
second toe)
Movements Allowed by Synovial Joints
• Circumduction (f):
– Is moving a limb so that it
describes a cone in the air
– Distal end of the limb moves
in a circle, while the point of
the cone (shoulder or hip
joint) is more or less
stationary
– Because circumduction
consists of flexion, abduction,
extension, and adduction
performed in succession, it is
the quickest way to exercise
the many muscles that
move the hip an shoulder
ball-and–socket joints
– Example:
• Pitcher winding up to throw a
ball
SYNOVIAL MOVEMENT
Movements Allowed by Synovial Joints
• Rotation (g):
– Is the turning of a bone
along its own long axis
– Only movement allowed
between the first two cervical
vertebrae and is common at
the hip and shoulder joints
– Examples:
• Medial rotation of the thigh:
– Femur’s anterior surface
moves toward the median
plane of the body
• Lateral rotation of the
thigh:
– Femur’s anterior surface
moves away from the
median plane of the body
SYNOVIAL MOVEMENT
Special Movements
• Certain movements do not fit into any of
the categories previously listed
Special Movements
• Supination and
Pronation: refer to the
movements of the
radius around the ulna
– (a): Supination (turning
backward) is rotating the
forearm laterally so that the
palm faces anteriorly or
superiorly
• In the anatomical position,
the hand is supinated and
the radius and ulna are
parallel
• Example:
– Lifting a cup of soup up
to your mouth on your
palm
Special Movements
• (a): Pronation (turning
forward) is rotating the
arm medially so that the
palm faces posteriorly or
inferiorly
– Moves the distal end of the
radius across the ulna so
that the two bones form an
X
– Forearm position when we
are standing in a relaxed
manner
– Example:
• Dribbling a basketball
BODY MOVEMENTS
Special Movements
• (b):Inversion and
Eversion are special
movements of the
foot
– Inversion turns the
sole of the foot so that
it faces medially
– Eversion turns the
sole of the foot so that
it faces laterally
BODY MOVEMENTS
Special Movements
• (c):Protraction and Retraction: nonangular anterior
and posterior movements in a transverse plane
– Examples:
• Protraction moves the mandible anteriorly, juts the jaw forward
• Retraction returns the mandible to its original position
BODY MOVEMENTS
Special Movements
• (d):Elevation and Depression:
– Elevation means lifting a body part superiorly
• Example:
– When you shrug your shoulders you are elevating the scapulae
– Depression means to move an elevated body part inferiorly
• Example:
– During chewing, the mandible is alternately elevated and depressed
BODY MOVEMENTS
Special Movements
• Opposition occurs when
you touch your thumb to
the tips of the other
fingers on the same hand
– Makes the human hand a
fine tool for grasping and
manipulating objects
• The saddle joint
between metacarpal 1
and the carpals allows
this movement
BODY MOVEMENTS
Types of Synovial Joints
• Although all synovial joints have structural features
in common, they do not have a common structural
features
• Based on the shape of their articular surfaces, which in
turn determine the movements allowed, synovial joints
can be classified further into six major categories:
–
–
–
–
–
–
1. Plane
2. Hinge
3. Pivot
4. Condyloid
5. Saddle
6. Ball-and-socket
Types of Synovial Joints
Plane (a)
• Have flat articular
surfaces and allow
gliding and transitional
movements
• Does not involve rotation
around any axis
• Only example of
nonaxial joints
• Examples:
– Intercarpal and intertarsal
joints
– Joints between vertebral
articular processes
SYNOVIAL JOINTS
Types of Synovial Joints
Hinge (b)
• (b): Consist of a cylindrical
projection on a bone that fits
into a trough-shaped
structure on another bone
• Movement is along a single
plane and resembles that of a
mechanical hinge
• Uniaxial hinge permits flexion
and extension only
• Examples:
– Bending and straightening the
elbow
– Interphalangeal joints
SYNOVIAL JOINTS
Types of Synovial Joints
Pivot (c)
• Consist of a rounded
structure that protrudes into
a sleeve or ring composed of
bone (and possibly
ligaments) of another bone
• Only movement allowed is
uniaxial rotation of one bone
around its own long axis
• Examples:
– Joint between the atlas and
dens of the axis, which
allows you to move your head
from side to side to indicate
“NO”
– Proximal radioulnar joint
• Head of the radius rotates
within a ringlike ligament
secured to the ulna
SYNOVIAL JOINTS
Types of Synovial Joints
Condyloid (d)
• Knuckle-like
• Ellipsoidal joint
• Consist of an oval articular
surface of one bone that fits
into a complementary
depression in another bone
• Both articular bones are oval
• Biaxial joint that permits all
angular movements (flexion,
extension, abduction,
adduction, and circumduction)
• Examples:
– Radiocarpal (wrist) joints
– Metacarpophalangeal
(knuckle) joints
SYNOVIAL JOINTS
Types of Synovial Joints
Saddle (e)
•
•
•
•
Resemble condyloid joints, but
they allow greater freedom of
movement
Saddle joints consist of each
articular surface bearing
complementary concave and
convex areas (shaped like a
saddle)
Allow more freedom of
movement than condyloid joints
Examples:
– Carpometacarpal joints of the
thumbs
• Movements allowed by
these joints are clearly
demonstrated by
twiddling your thumbs
SYNOVIAL JOINTS
Types of Synovial Joints
Ball-and-Socket (f)
• Consist of a spherical or
hemispherical head
structure that articulates
with a cuplike socket
structure
• They are the most freely
moving joints
• Allow multiaxial movements
– Universal movement is
allowed (in all axes and
planes, including rotation)
• Examples:
– Shoulder
– Hip
SYNOVIAL JOINTS
Knee Joint
•
•
•
Knee joint is the largest and most
common complex joint in the body
It allows extension, flexion, and some
rotation
Despite its single joint cavity, the knee
consists of three joints in one:
– An intermediate:
• One between the patella and the
lower end of the femur
(femoropatellar joint)
– Lateral and medial joints (collectively
known as the tibiofermoral joint)
between the femoral condyles above
and the C-shaped menisci, or
semilunar cartilages, of the tibia below
• Besides deepening the shallow
tibial articular surfaces, the
menisci help prevent side-toside rocking of the femur on the
tibia and absorb shock
transmitted to the knee joint
KNEE JOINT
KNEE JOINT
Knee Joint
Anterior View
• Many different types of
ligaments stabilize and
strengthen the capsule
of the knee joint
– The patellar ligament and
retinacula are actually
continuations of the tendon
of the bulky quadriceps
muscles of the anterior
thigh
• Physicians tap the
patellar ligament to test
the knee-jerk reflex
KNEE JOINT
KNEE JOINT
Knee Joint
Lateral View
• The synovial cavity of the
knee joint has a
complicated shape, with
several extensions that
lead into “blind alleys”
• At least a dozen bursae
are associated with this
joint
– The subcutaneous
perpatellar bursa is often
injured when the knee is
bumped
KNEE JOINT
Lateral View
Knee Joint
• All three types of joint ligaments
stabilize and strengthen the capsule of
the knee joint
• The capsular and extracapsular
ligaments all act to prevent
hyperextension of the knee and are
stretched taut when the knee is extended
Knee Joint
Anterior View
• Extracapsular
fibular and tibial
collateral ligaments:
– Prevent lateral or
medial rotation when
knee is extended
KNEE JOINT
Knee Joint
Posterior View
• Oblique popliteal
ligament:
– Is actually part of the
tendon of the
semimembranous
muscle that fuses with
the capsule and
strengthens the
posterior aspect of
the knee joint
KNEE JOINT
Knee Joint
Posterior View
• Arcuate popliteal
ligament:
– Arcs superiorly from
the head of the fibula
and reinforces the joint
capsule posteriorly
KNEE JOINT
Knee Joint
• Intracapsular ligaments
are called cruciate
ligaments because they
cross each other,
forming an X in the
notch between the
femoral condyles
– Help prevent anteriorposterior displacement of
the articular surfaces and
secure the articulating
bones when we stand
KNEE JOINT
HOMEOSTATIC IMBALANCE
• Of all body joints, the knees are most
susceptible to sports injuries because
of their high reliance on nonarticular
factors for stability and the fact that
they carry the body’s weight
• The knee can absorb a vertical force
equal to nearly seven times body weight
– However, it is very vulnerable to horizontal
blows, such as those that occur during
blocking and tackling in football
HOMEOSTATIC IMBALANCE
Anterior View of Medial Knee Injury
• When thinking of
common knee injuries,
remember the 3 C’s:
– 1. Collateral ligaments:
• Most dangerous are
lateral blows to the
extended knee
• These forces tear the tibial
collateral ligament and the
medial meniscus attached
to it, as well as the
anterior cruciate ligament
KNEE INJURY
HOMEOSTATIC IMBALANCE
• 2. Cruciate ligaments: Anterior Cruciate
Ligament (ACL)
– Most ACL injuries occur when a runner
changes direction quickly, twisting a
hyperextended knee
– A torn ACL heals poorly, so repair usually
requires a ligament graft using connective
tissue taken from one of the larger ligaments
(e.g., patellar, Achilles, or semitendinosus)
Shoulder (Glenohumeral ) Joint
• Stability has been
sacrificed to provide
the most freely moving
joint in the body
• Is a ball-and-socket
joint:
– Large hemispherical head
of the humerus fits in the
small, shallow glenoid
cavity of the scapula (like a
golf ball setting on a tee)
Shoulder (Glenohumeral ) Joint
• The ligaments that
help to reinforce the
shoulder joint are
the coracohumeral
ligament and the
three glenohumeral
ligaments
SHOULDER JOINT
SHOULDER JOINT
Shoulder (Glenohumeral ) Joint
• The tendons that cross
the shoulder joint
provide the most
stabilizing effect on the
joint:
– These tendons and
associated muscles
(subscapularis,
supraspinatus,
infraspinatus, and teres
minor) make up the rotator
cuff
• This cuff encircles the
shoulder joint and blends
with the articular capsule
SHOULDER MUSCLES
SHOULDER MUSCLES
SHOULDER JOINT
SHOULDER JOINT
SHOULDER JOINT
Shoulder (Glenohumeral ) Joint
• The rotator cuff can be severely stretched
when the arm is vigorously circumducted
(movement of a body part so that it outlines a
cone in space)
– This is a common injury of baseball pitchers
• Dislocation:
– Because the shoulder’s reinforcements are weakest
anteriorly and inferiorly, the humerus tends to
dislocate in the forward and downward direction
Hip (Coxal) Joint
•
The hip joint is a ball-and-socket joint that provides a good range of
motion:
– Not nearly as wide as the shoulder’s range of motion
– Movements occur in all possible planes but are limited by the joint’s strong
ligaments and its deep sockets
•
The hip joint is formed by the articulation of the spherical head of the
femur with the deeply cupped acetabulum of the hip bone
– The depth of the acetabulum is enhanced by a circular rim of fibrocartilage called
the acetabular labrum
HIP JOINT
Hip (Coxal) Joint
•
•
(c): anterior view
(b): posterior view
Several strong ligaments reinforce the capsule of the hip joint
– These ligaments are arranged in such a way that they “screw” the femur
head into the acetabulum when a person stands up straight, thereby providing
more stability
•
The muscle tendons that cross the joint contribute to the stability and
strength of the joint, BUT the majority of the stability of the hip joint is
due to the deep socket of the acetabulum and the ligaments
HIP JOINT
Elbow Joint
• The elbow joint provides a stable and smoothly operating hinge
joint that ONLY allows flexion and extension
• Within the joint, both the radius and ulna articulate with the
condyles of the humerus but it is the close gripping of the
trochlea by the ulna’s trochlear notch that forms the “hinge”
and stabilizes this joint
• (b): lateral view
ELBOW JOINT
Elbow Joint
• The ligaments involved in providing stability to the elbow joint
are the annular ligament, the ulnar collateral ligament, and the radial
collateral ligament
• Tendons of several arm muscles, the biceps and the triceps,
also provide additional stability by crossing the elbow joint
• The radius is a passive “onlooker” in the angular elbow movements
– However, its head rotates within the angular ligament during supination
and pronation of the forearm
ELBOW JOINT
Common Joint Injuries
• Sprains
– The ligaments reinforcing a joint are stretched or torn
– Partially torn ligaments will repair themselves, but they heal
slowly because ligaments are so poorly vascularized
– Tend to be painful and immobilizing
– Completely ruptured ligaments require prompt surgical
repair because inflammation in the joint will break down the
neighboring tissues and turn the injured ligament to “mush”
• Surgery requires sewing hundreds of fibrous strands (NOT
EASY)
– Examples:
• Lumbar region of the spine, the ankle, and the knee are
common sprain sites
Common Joint Injuries
• Cartilage:
– Although most cartilage injuries involve tearing of
the knee menisci, overuse damage to the articular
cartilages of other joints is becoming increasingly
common in competitive young athletes
– Is avascular and it rarely can obtain sufficient
nourishment to repair itself; thus, it usually stays
torn:
• Because cartilage fragments (called loose bodies) can
interfere with joint function by causing the joint to lock or
bind, most sports physicians recommend that the central
(nonvascular) part of a damaged cartilage be removed
Common Joint Injuries
• Cartilage:
– Arthroscopic surgery:
• A small instrument bearing a
tiny lens and fiber-optic light
source, enables the surgeon
to view the joint interior
– Repair ligament
– Remove cartilage fragments
– Removal of part of a
meniscus
» Removal of part of a
meniscus does not
severely impair joint
mobility, but the joint
is definitely less
stable
• Minimizes tissue damage and
scarring
JOINT INJURY
Common Joint Injuries
• Dislocation: luxation
– Occurs when bones are forced out of alignment
• Usually accompanied by sprains, inflammation, and joint
immobilization
– Like fractures, dislocations must be reduced
(bone ends must be returned to their proper
positions)
– Examples:
•
•
•
•
Jaw
Shoulder
Fingers
Thumb
– Subluxation: partial dislocation of a joint
Inflammatory and Degenerative Conditions
• Bursitis:
– Inflammation of the bursa
• Is usually caused by a blow or friction
– Severe cases are treated by injecting antiinflammatory drugs into the bursa
– If excessive fluid accumulates, removing some fluid
by needle aspiration may relieve the pressure
– Examples:
• Falling on one’s knee may result in a painful bursitis of the
prepatellar bursa (housemaid’s knee / water on the knee)
• Prolonged leaning on one’s elbow may damage the bursa
close to the olecranon process (student’s elbow /
olecranon bursitis)
Inflammatory and Degenerative Conditions
• Tendonitis:
– Is inflammation of the tendon sheaths, and
is usually caused by overuse
– Symptoms: pain and swelling
– Treatment: rest, ice, anti-inflammatory drugs
Inflammatory and Degenerative Conditions
• Arthritis:
– Describes many inflammatory or degenerative
diseases (over 100) that damage the joints
– Resulting in pain, stiffness, and swelling of the joint
– Acute forms:
• Usually result from bacterial invasion and are treated with
antibiotics
• Synovial membrane thickens and fluid production decreases,
causing increased friction and pain
– Chronic (long-term) forms: osteoarthritis,
rheumatoid arthritis, and gouty arthritis
Inflammatory and Degenerative Conditions
• Osteoarthritis (OA):
– Most common chronic arthritis
– Often called “wear-and-tear” arthritis
– Probably related to aging
• But a genetic basis
– Slow and irreversible
– It is the result of breakdown of articular cartilage (by enzymes: but
in healthy people replaced) and subsequent thickening of bone
tissue, which may restrict joint movement
• Cartilage softened, roughened, pitted, and eroded
– Treatment:
• Aspirin, acetaminophen, magnetic therapy (assumed to stimulate the
growth and repair of articular cartilage), glucosamine (nutritional
supplement: decrease pain and inflammation, preserve articular cartilage)
– Examples: cervical and lumbar spines, fingers, knuckles, knees, hips
Inflammatory and Degenerative Conditions
•
Rheumatoid arthritis:
– Chronic inflammatory disorder that is
an autoimmune disease
• Disorder in which the body’s
immune system attacks its own
tissues
– Microorganisms that bear
chemicals similar to some
naturally present in the
joints
» BOTH are attacked
by the immune
system
– Any age
– Examples:
• Many joints, particularly the small
joints of the fingers, wrists, ankles,
and feet
– Afflicted at the same time
and bilaterally (right and
left sides)
– Treatment: anti-inflammatory and
immunosuppressant drugs
ARTHRITIS
Inflammatory and Degenerative Conditions
• Gouty Arthritis: gout
– Uric acid, a normal waste product of nucleic acid metabolism, is
ordinarily excreted in urine without any problems
– However, when blood levels of uric acid rise excessively (due
to its excessive production or slow excretion), it may be
deposited as needle-shaped urate crystals in the soft
tissues of joints
• Inflammatory response follows
– Genetic factors are definitely implicated
– Untreated:
• Articular bone ends fuse and immobilizes the joints
– Treatment:
• Anti-inflammatory drugs
• Avoid alcohol: promotes uric acid overproduction
• Avoid foods high in purine-containing nucleic acids (liver, kidneys,
sardines)
ARTIFICIAL JOINT
DEVELOPMENTAL ASPECTS
OF
JOINTS
• Joints develop at the same time as bones,
resembling adult form by eight weeks
gestation
• At late middle age and beyond, ligaments
and tendons shorten and weaken,
intervertebral discs become more likely to
herniate, and there is onset of
osteoarthritis