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Joints
Slides by Vince Austin and W. Rose.
figures from Marieb & Hoehn 7th and 8th eds.
Portions copyright Pearson Education
Joints (Articulations)

Weakest parts of the skeleton

Articulation – site where two or more bones meet

Functions of joints

Give the skeleton mobility

Hold the skeleton together
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Classification of Joints: Structural

Structural classification focuses on the material
binding bones together and whether or not a joint
cavity is present

The three structural classifications are:

Fibrous

Cartilaginous

Synovial
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Classification of Joints: Functional

Functional classification is based on the amount of
movement allowed by the joint

The three functional classes of joints are:

Synarthroses – immovable

Amphiarthroses – slightly movable

Diarthroses – freely movable
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Fibrous Structural Joints

The bones are joined by fibrous tissues

There is no joint cavity

Most are immovable

There are three types – sutures, syndesmoses, and
gomphoses
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Fibrous Structural Joints: Sutures

Occur between the bones of the skull

Comprised of interlocking junctions completely
filled with connective tissue fibers

Bind bones tightly together, but allow for growth
during youth

In middle age, skull bones fuse and are called
synostoses
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Fibrous Structural Joints: Sutures
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Figure 8.1a
Fibrous Structural Joints: Syndesmoses

Bones are connected by a fibrous tissue ligament

Movement varies from immovable to slightly
variable

Examples include the connection between the tibia
and fibula, and the radius and ulna
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Fibrous Structural Joints: Syndesmoses
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Figure 8.1b
Fibrous Structural Joints: Gomphoses

The peg-in-socket fibrous joint between a tooth
and its alveolar socket

The fibrous connection is the periodontal ligament
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Cartilaginous Joints

Articulating bones are united by cartilage

Lack a joint cavity

Two types – synchondroses and symphyses
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Cartilaginous Joints: Synchondroses

A bar or plate of hyaline cartilage unites the bones

All synchondroses are synarthrotic

Examples include:

Epiphyseal plates of children

Joint between the costal cartilage of the first rib
and the sternum
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Cartilaginous Joints: Synchondroses
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Figure 8.2a, b
Cartilaginous Joints: Symphyses

Hyaline cartilage covers the articulating surface of
the bone and is fused to an intervening pad of
fibrocartilage

Amphiarthrotic joints designed for strength and
flexibility

Examples include intervertebral joints and the
pubic symphysis of the pelvis
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Cartilaginous Joints: Symphyses
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Figure 8.2c
Synovial Joints

Those joints in which the articulating bones are
separated by a fluid-containing joint cavity

All are freely movable diarthroses

Examples – all limb joints, and most joints of the
body
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Joints: Structural Classification
Fibrous
Cartilaginous
Sutures
Syndesmoses
Gomphoses
Synchondroses
Symphyses
Synovial
Most sophisticated structure
Hyaline cartilage on
joint surfaces
Synarthrotic
Cranial
Synarthrotic or
amphiarhtrotic
Synarthrotic
All are synarthrotic
All are amphiarthrotic
All are diarthrotic
Teeth
rib1-manubrium;
epiphyseal plates
Pubic, intervertebral
Most joints in body
Tibiofibular,
radioulnar
Joints: Functional Classification
Synarthroses
Amphiarthroses
Diarthroses
no movement
slight movement
Most fibrous joints (except some All symphyses
syndesmoses)
Some syndesmoses
All synchondroses
free movement
All synovial joints
Synovial Joints: General Structure

Synovial joints all have the following

Articular cartilage

Joint (synovial) cavity

Articular capsule

Synovial fluid

Reinforcing ligaments
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Synovial Joints: General Structure
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Figure 8.3a, b
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Table 8.2.1
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Table 8.2.2
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Table 8.2.3
Synovial Joints: Friction-Reducing Structures



Bursae – flattened, fibrous sacs lined with synovial
membranes and containing synovial fluid
Common where ligaments, muscles, skin, tendons,
or bones rub together
Tendon sheath – elongated bursa that wraps
completely around a tendon
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Synovial Joints: Friction-Reducing Structures
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Figure 8.4
Synovial Joints: Stability

Stability is determined by:


Articular surfaces – shape determines what
movements are possible
Ligaments – unite bones and prevent excessive or
undesirable motion
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Synovial Joints: Stability

Muscle tone is accomplished by:

Muscle tendons across joints acting as stabilizing
factors

Tendons that are kept tight at all times by muscle
tone
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Synovial Joints: Movement


The two muscle attachments across a joint are:

Origin – attachment to the immovable bone

Insertion – attachment to the movable bone
Described as movement along transverse, frontal,
or sagittal planes
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Synovial Joints: Range of Motion

Nonaxial – slipping movements only

Uniaxial – movement in one plane

Biaxial – movement in two planes

Multiaxial – movement in or around all three
planes
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Gliding Movements


One flat bone surface glides or slips over another
similar surface
Examples – intercarpal and intertarsal joints, and
between the flat articular processes of the vertebrae
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Angular Movement



Flexion — bending movement that decreases the
angle of the joint
Extension — reverse of flexion; joint angle is
increased
Dorsiflexion and plantar flexion — up and down
movement of the foot
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Angular Movement

Abduction — movement away from the midline

Adduction — movement toward the midline

Circumduction — movement describes a cone in
space
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Gliding Movement
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Figure 8.5a
Angular Movement
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Figure 8.5b
Angular Movement
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Figure 8.5c, d
Angular Movement
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Figure 8.5e, f
Rotation

The turning of a bone
around its own long axis

Examples

Between first two
vertebrae

Hip and shoulder joints
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Figure 8.5g
Special Movements

Supination and pronation

Inversion and eversion

Protraction and retraction

Elevation and depression

Opposition
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Special Movements
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Figure 8.6a
Pronation and Supination at the Ankle
At ankle:
Pronation  Eversion* (see next slide)
Supination  Inversion*
Normal Gait: Heel strikes on lateral portion with ankle slightly
inverted and plantar flexed . This is the supinated position.
Then pronation occurs as rest of foot comes down: ankle
moves into eversion (weight shifts medially) and dorsiflexion.
It was long thought that overpronation or underpronation
(above or below average eversionwas a cause of foot, ankle,
knee injuries. Shoe companies marketed “motion control”
shoes. However there is evidence that over/underpronators are
not more injury prone, and that moderate overpronators may
have fewer injuries than “neutral” runners.
*Supination is inversion plus plantarflexion and adduction: a triplanar motion involving the
Special Movements
 supination
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 pronation
Figure 8.6b
Right foot, posterior view
www.bostonrunningcompany.com.com
Overpronation.
www.bostonrunningcompany.com
Evenly distributed
wear
Excessive lateral
wear
Excessive medial
wear
Bottom of a right shoe. Red areas are worn down. Some evidence
suggests picking shoes to match the runner’s ankle motion leads to
more, not fewer, injuries. (A, B) Image: www.therunningshop.uk.com
Varus and Valgus
Describe alignment of two segments in the frontal (coronal) plane.
Varus alignment: distal segment
deviates medially relative to
proximal segment.
Valgus alignment: distal segment
deviates laterally relative to
proximal segment.
Varus, valgus often used to describe
alignment at knee and ankle.
Valgus at the knee: “knock-kneed”
Varus at the knee: “bow-legged”
Bunion: hallux valgus
Left Knee, Anterior View
Valgus
Varus
Proximal
segment
Medial
Distal seg.
Lateral
Proximal
segment
Medial
Lateral
Distal seg.
Talocrural Joint
Ankle Joint (talus to lower leg = crural region)
Ankle sprain – most common joint injury
• Low ankle sprain: tear of ligaments “below the ankle”
• Inversion sprain – more common – damage to lateral
ligaments (ant. & post. talofibular, calcaneofibular)
• Eversion – damage to medial (deltoid) ligament
• High ankle sprain: tear of ligaments “above the ankle”
• Tear of syndesmotic ligaments of distal tibiofibular
joint (tibiofibular joints are syndesmotic, a subset of
fibrous, and amphiarthrotic, i,.e. slightly movable.)
• High ankle sprain generally takes longer to heal.
Special Movements
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Figure 8.6c
Special Movements
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Figure 8.6e