Chapter 8: Joints
Joints or articulations:
 Sites where 2 or more bones meet
 2 fundamental functions; give our skeleton mobility, and
they hold it together playing a protective role.
 They are the weakest parts of the skeleton
Classification of joints; Structure and Function
 Structural classification focuses on the material binding
the bones together and whether or not a joint cavity is
present
o Fibrous joints (mostly immoveable)
o Cartilagenous joints (both rigid and slightly
moveable)
o Synovial joints (freely movable)
 Functional classification
o Based on the movement allowed at the joint
 Synarthroses (syn=together, arthro=joint) these
are immovable joints – axial skeleton
 Amphiarthroses (amphi=both sides) these are
slightly moveable joints – axial skeleton
 Diarthroses: (dia=through or apart) are freely
movable joints – appendicular skeleton
Fibrous Joints
 Bones joined by fibrous tissue with no joint cavity present
 The amount of movement depends on the length of
connective tissues joining the bones. Most fibrous joints
are immoveable.
o 3 types:
 Sutures, (seams) the bones of your skull
 Syndesmoses, (syndesmos = ligament) end of the
tibia and fibula has “give” but not really
moveable
 Gomphoses (nail or bolt) refers to the way teeth
are embedded in their sockets
Cartilaginous Joints:
 The articulating bones are united by cartilage
 They also lack a joint cavity
 2 types:
o Synchondroses (junction of cartilage)
o Symphysis (growing together)
Synchondroses:
 A bar or plate of hyaline cartilage unites bones at
synchodroses
 All are synarthrotic
 Most common are the epiphyseal plates between the
epiphysis and diaphysis of long bones
o These are temporary joints
Symphysis:
 The articular surfaces of bones are covered with articular
(hyaline) cartilage, which is fused to a pad or plate of
fibrocartilage. The fibrocartilage is compressible and
resilient and acts as a shock absorber permitting a limited
amount of movement
 They are amphiarthrotic joints designed for strength with
flexibility – intervertebral joints and pubic symphysis
Synovial Joints:
o Bones are separated by a fluid containing joint cavity
o This allows for substantial movement
o All synovial joints are freely movable diarthroses
Synovial joints have 5 distinguishing characteristics:
o Articular cartilage – glassy smooth hyaline cartilage
cushions and absorbs compression placed on the joint
o Joint cavity – a space that contains a small amount of
synovial fluid
o Articular capsule – also known as the joint capsule an
outer layer of fibrous connective tissue continuous with
the periostea of the articulating bones and the inner
layer (synovial membrane) composed of loose
connective tissue
o Synovial fluid – slippery occupies the free spaces within
the joint capsule.
o This fluid is filtered from the blood flowing through
the capillaries in the synovial membrane. It is also
found within the articular cartilage.
 Provides a slippery weight-bearing film that
reduces friction between the cartilages.
 Also is forced out of the cartilage when
compressed and then seeps back in with the
pressure is released. “Weeping lubrication”
o Reinforcing ligaments –
o Synovial joints are reinforced and strengthened by
a number of band-like ligaments
o Some joints contain fibrocartilage discs that
increase the fit and absorb shock
o Bursae and Tendon Sheaths
o Bags of lubricant, they act like ball bearings to
reduce friction between adjacent structures during
activity.
o Bursae are flattened fibrous sacs lined with
synovial membrane containing a thin film of
synovial fluid.
o Tendon Sheath is an elongated bursa that wraps
completely around a tendon subjected to friction
(like a bun around a hotdog)
Factors influencing the stability of synovial joints
 Articular surfaces
o Shapes of the articular surfaces determine what
movements are possible at a joint
o Only a minor role in the stability of joints
 The ball and socket joint of the hip is an example
of a joint made extremely stable by the shape of
its articular surface
 Ligaments
o As a rule: the more ligaments a joint has the stronger
it is
 The problem: Stretched ligaments stay stretched
- ligaments stretch like taffy
 A ligament can only stretch about 6% of its
length before it snaps
 Muscle Tone
o For most joints, the muscle tendons that cross the
joint are the most important stabilizing factor
o Muscle tone is extremely important in reinforcing the
shoulder, knee and arches of the foot
Movements allowed by the Synovial Joints
 Every skeletal muscle of the body is attached to bone or
other connective tissue structures at no fewer than 2
points.
o Muscle Origin: is attached to the immovable (or less
movable) bone.
o Muscle Insertion: is attached to the movable bone
 Body movement occurs when muscles contract across
joints and their insertion moves toward its origin
 Movements are described in directional terms relative to
the lines, or axes, around which the body part moves and
the planes of space along which the movement occurs,
along the transverse, frontal, or sagittal plane.
o Range of motion allowed by synovial joints varies :
 Nonaxial movement (slipping movements only,
no axis around which the movement can occur)
 Uniaxial movement: movement in one plane
 Biaxial movement: movement in 2 planes
 Multiaxial movement: movement in or around
all 3 planes of space or axes.
o 3 General types of movement
 Gliding: also known as translation, are the
simplest joint movements. Occur at intercarpal
and intertarsal joints and in between flat
articular processes of the vertebrae
 Angular: increase and decrease the angle
between 2 bones. They may occur in any plane
of the body and include: flexion, extension,
hyperextension, abduction, adduction and
circumduction
 Rotation: is the turning of a bone around its long
axis. May be directed toward the midline of body
or away from it.
 Only movement allowed between the first 2
vertebra and the hip and shoulder
Special Movements:
 Certain movements don’t fit into any of the above
categories and occur at only few joints (p 262-63)
o Supination and Pronation (“turning backward,
turning forward”) forearm rotations
o Inversion and Eversion:
 special movements of the foot
 Inversion – turning the sole of the foot
medially (inward)
 Eversion – turning the sole of the foot
laterally (out)
o Protraction and Retraction
 Done in the transverse plane, the mandible is
protracted when you jut out your jaw, retracted
when it returns to normal position
o Elevation and Depression
 Elevation means lifting a body part superiorly,
when you shrug your shoulders you elevate your
scapula. Depression is moving the elevated part
inferiorly
o Opposition
 The saddle joint between metacarpal 1 and the
carpals allows this movement of the thumb to
finger tips
Types of Synovial Joints (p264)
 Plane joints
o Articular surfaces are essentially flat and allow only
short gliding or translational movements, wrists and
ankles
 Hinge joints
o Projection of one bone fits in a trough shaped surface
of another
o Motion is along a single plane and resembles a
mechanical hinge – elbow, fingers
 Pivot joints
o The rounded end of one bone protrudes into a
“sleeve” or ring of bone (possibly ligaments) of
another
o Uniaxial rotation, Ex. Atlas and the dens of the Axis
“shaking your head no”. another example: head of
the radius and the ring like ligament attached to the
ulna
 Condyloid joints: “knuckle like”
o Oval articular surface of one bone fits into a
complimentary depression in another
o Both articulating surfaces are oval
o Biaxial condyloid joints permit angular motions:
flexion extension, abduction, adduction,and
circumduction. EX. radiocarpal (wrist) and
metacarpophalangeal (knuckle) joints
 Saddle joints:
o Resemble condyloid joints but offer greater
movement
 Each articular surface has both concave and
convex areas; that is, it is shaped like a saddle
 Carpometacarpal joints of the thumbs.
 Movements allowed “twiddling your thumbs”
 Ball and socket joints:
o The spherical or hemispherical head of one bone
articulates with the cuplike socket of another
o These are multiaxial and the most freely moving
synovial joints
 Universal movement allowed (all axes, and
planes including rotation) Ex. Shoulders, Hips
Knee Joint:
 Largest and most complex joint in the body
 Allows extension, flexion, and some rotation
 Actually 3 joints in one:
o Intermediate joint between the patella and the lower
end of the femur (femoropatellar joint)
o Lateral and medial joints (collectively known as the
tibiofemoral joints)
 Articular surfaces are shallow and condyloid.
o C-shaped menisci deepen the articular surfaces
o The joint cavity is enclosed by a capsule only on the
sides and posterior aspects
o Several ligaments help prevent displacement
o Muscle tone of quadriceps and semimembranosus
muscles is important to knee stability
The elbow:
 A hinge joint in which the ulna and radius articulate with
the humerus, allowing flexion and extension
 Articular surfaces are highly complementary and are the
most important factor contributing to joint stability
The Shoulder:
 Ball and socket joint formed by the glenoid cavity of the
scapula and the head of the humerus
 The most freely movable joint in the body, it allows for all
angular and rotational movements
 Articular surfaces are shallow
 Its capsule is lax and poorly reinforced by ligaments
 The tendons of the biceps brachii and rotator cuff muscles
help stabilize it
The Hip:
 Ball and socket joint formed by the coxal bone and femoral
head
 Highly adapted for weight bearing
 Articular surfaces are deep and secure
 Its capsule is heavy and strongly reinforced by ligaments
The Temporomandibiluar joint:
 Formed by the mandibular condyle and the mandibular
fossa and articular tubercle of the temporal bone
 Joint allows both a hinge-like opening and closing of the
mouth and an anterior gliding of the mandible.
 It often dislocates anteriorly and exhibits a number of TMJ
disorders
Homeostatic Imbalances of Joints:
 Sprains:
o Involve the stretching or tearing of joint ligaments.
Because ligaments are poorly vascularized the healing
is slow
 Cartilage injuries
o Particularly in the knee, are common in contact sports
and may result from excessive twisting or high
pressure
o The avascular cartilage is unable to repair itself
 Dislocations:
o Involve the displacement of articular surfaces and
must be reduced
Inflammatory and Degenerative Conditions:
 Bursitis and tendonitis are inflammation of the bursa and
tendon sheath
 Arthritis is joint inflammation or degeneration
accompanied by stiffness, pain, and swelling.
o Acute forms generally result from bacterial infections
o Chronic conditions include osteoarthritis, rheumatoid
arthritis and gouty arthritis
o Osteoarthritis is a degenerative condition most
common in the older folks. Weight-bearing joints are
most affected
o Rheumatoid arthritis is the most crippling arthritis, is
an autoimmune disease involving severe
inflammation of the joints
o Gouty arthritis is joint inflammation caused by the
deposit of urate salts in the soft joint tissues
Developmental aspects of joints:
 Joints form from the mesenchyme and in tandem with the
bone development in the embryo
 Excluding traumatic injury, joints usually function well until
late middle age. Prudent exercise delays the effects,
whereas excessive exercise promotes early onset of
arthritis