Chapter 9
Articulations
Introduction
 Articulation—point of contact between bones
 Joints are mostly very movable, but others are immovable or allow only limited
motion
 Movable joints allow complex, highly coordinated, and purposeful movements
to be executed
Classification of Joints
 Joints may be classified using a structural or functional scheme (Table 9-1)
Structural classification—joints are named according to one of the following:
• Type of connective tissue that joins bones together (fibrous or
cartilaginous joints)
• Presence of a fluid-filled joint capsule (synovial joint)
 Functional classification—joints are named according to degree of
movement allowed:
• Synarthroses—immovable joint
• Amphiarthroses—slightly movable
• Diarthroses—freely movable
 Fibrous joints (synarthroses)—bones of joints fit together closely, allowing little
or no movement (Figure 9-1)
 Syndesmoses—joints in which ligaments connect two bones
 Sutures—found only in skull; toothlike projections from adjacent bones
interlock with each other
 Gomphoses—between root of a tooth and the alveolar process of the
mandible or maxilla
 Cartilaginous joints (amphiarthroses)—bones of joints are joined together by
hyaline cartilage or fibrocartilage; allow very little motion (Figure 9-2)
 Synchondroses—hyaline cartilage present between articulating bones (ribs)
 Symphyses—joints in which a pad or disk of fibrocartilage connects two
bones (symphysis pubis)
 Synovial joints (diarthroses)—freely movable joints (Figure 9-3)
 Structures of synovial joints
• Joint capsule—sleevelike casing around ends of bones, binding them
together
• Synovial membrane—lines joint capsule and also secretes synovial fluid
• Articular cartilage—hyaline cartilage covering articular surfaces of bones
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Classification of Joints
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Structures of synovial joints (cont.)
• Joint cavity—small space between the articulating surfaces of the two
bones of the joint
• Menisci (articular disks)—pads of fibrocartilage located between
articulating bones
• Ligaments—strong cords of dense, white, fibrous tissue that hold bones
of synovial joint more firmly together
• Bursae—synovial membranes filled with synovial fluid; cushion joints
and facilitate movement of tendons
Types of synovial joints (Figure 9-4)
• Uniaxial joints—synovial joints that permit movement around only one
axis and in only one plane
 Hinge joints—articulating ends of bones form a hinge-shaped unity
that allows only flexion and extension
 Pivot joints—a projection of one bone articulates with a ring or notch
of another bone
• Biaxial joints—synovial joints that permit movements around two
perpendicular axes in two perpendicular planes
 Saddle joints—synovial joints in which the articulating ends of the
bones resemble reciprocally shaped miniature saddles; only
occurrence in body is in thumbs
 Condyloid (ellipsoidal) joints—synovial joints in which a condyle fits
into an elliptical socket
• Multiaxial joints—synovial joints that permit movements around three or
more axes in three or more planes
 Ball and socket (spheroid) joints—most movable joints; ball-shaped
head of one bone fits into a concave depression
 Gliding joints—relatively flat articulating surfaces that allow limited
gliding movements along various axes
Representative Synovial Joints
 Humeroscapular joint (Figure 9-5)
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Shoulder joint
Most mobile joint because of the shallowness
of the glenoid cavity
Glenoid labrum—narrow rim of fibrocartilage around glenoid cavity that
lends depth to the cavity
Structures that strengthen the shoulder joint are ligaments, muscles,
tendons, and bursae
Representative Synovial Joints
 Elbow joint (Figure 9-6)
Humeroradial joint—lateral articulation of capitulum of humerus with head
of radius
 Humeroulnar joint—medial articulation of trochlea of humerus with trochlear
notch of ulna
 Both components of elbow joint surrounded by single joint capsule and
stabilized by collateral ligaments
 Classic hinge joint
 Medial and lateral epicondyles are externally palpable bony landmarks
 Olecranon bursa independent of elbow joint space—inflammation called
olecranon bursitis
• Trauma to nerve results in unpleasant sensations in those fingers and
part of hand supplied by nerve; severe injury may cause “wrist drop”
 Proximal radioulnar joint—between head of radius and medial notch of ulna
 Stabilized by annular ligament
 Permits rotation of forearm
 Dislocation of radial head called “pulled elbow”
 Distal radioulnar joint—point of articulation between ulnar notch of radius and
head of ulna
 Together with proximal radioulnar joint, permits pronation and supination of
forearm
 Radiocarpal (wrist) joints (Figure 9-7)
 Only radius articulates directly with carpal bones distally (scaphoid and
lunate)
 Joints are synovial
 Scaphoid bone is fractured frequently
 Portion of fractured scaphoid may become avascular
 Intercarpal joints (Figure 9-7)
 Between 8 carpal bones
 Stabilized by numerous ligaments
 Joint spaces usually communicate
 Movements generally gliding, with some
abduction and flexion
 Carpometacarpal joints—total of three joints
 One joint for thumb—wide range of movements
 Two joints for fingers—movements largely gliding type
 Thumb carpometacarpal joint is unique and important functionally
• Loose-fitting joint capsule
• Saddle-shaped articular surface
• Movements—extension, adduction, abduction, circumduction, and
opposition
• Opposition—ability to touch tip of thumb to tip of other fingers—
movement of great functional significance
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Representative Synovial Joints
 Metacarpophalangeal joints (Figure 9-8)
Rounded heads of metacarpals articulate with concave bases of proximal
phalanges
 Capsule surrounding joints strengthened by collateral ligaments
 Primary movements are flexion and extension
 Interphalangeal joints
 Typical diarthrotic, hinge-type, synovial joints
 Occur between heads of phalanges and bases
of more distal phalanges
 Two categories:
• PIP joints—proximal interphalangeal joints
(between proximal and middle phalanges)
• DIP joints—distal interphalangeal joints
(between middle and distal phalanges)
 Hip joint (Figure 9-9)
 Stable joint because of shape of head of femur and of acetabulum
 A joint capsule and ligaments contribute to joint’s stability
 Knee joint (Figures 9-10 and 9-11)
 Largest and one of most complex and most frequently injured joints
 Tibiofemoral joint is supported by a joint capsule, cartilage, and numerous
ligaments and muscle tendons
 Permits flexion and extension and, with knee flexed, some internal and
external rotation
 Ankle joint (Figure 9-12)
 Hinge type of synovial joint
 Articulation between lower ends of tibia and fibula and upper part of talus
 Joint is “mortise” or wedge-shaped
• Lateral malleolus lower than medial
 Internal rotation injury results in common “sprained ankle”
• Involves anterior talofibular ligament
 Other ankle ligaments may also be involved in sprain injuries—example is
deltoid ligament
 External ankle rotation injuries generally involve bone fractures rather than
ligament tears
• First-degree ankle injury—lateral malleolus fractured
• Second-degree ankle injury—both malleoli fractured
• Third-degree ankle injury—fracture of both malleoli
and articular surface of tibia
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Representative Synovial Joints
 Vertebral joints (Figures 9-13 and 9-14)
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Vertebrae are connected to one another by several joints to form a strong,
flexible column
Bodies of adjacent vertebrae are connected by intervertebral disks and
ligaments
Intervertebral disks are made up of two parts:
• Annulus fibrosus—disk’s outer rim, made of fibrous tissue and
fibrocartilage
• Nucleus pulposus—disk’s central core, made of a pulpy, elastic
substance
Types and Range of Movement at Synovial Joints
 Measuring range of motion (Figure 9-14)
Range of motion (ROM) assessment used to determine extent of joint injury
ROM can be measured actively or passively; results of both methods
generally about equal
 ROM measured by instrument called a goniometer
 Angular movements—change the size of the angle between articulating bones
 Flexion—decreases the angle between bones; bends or folds one part on
another (Figures 9-15, A, 9-17, and 9-18)
 Extension and hyperextension (Figure 9-17)
• Extension—increases the angle between bones, returns a part from its
flexed position to its anatomical position
• Hyperextension—stretching or extending part beyond its anatomical
position (Figures 9-18, 9-20, and 9-22)
 Plantar flexion and dorsiflexion (Figure 9-24)
• Plantar flexion—increases angle between top of foot and front of leg
• Dorsiflexion—decreases angle between top of foot and front of leg
 Abduction and adduction (Figures 9-18 and 9-22)
• Abduction—moves a part away from median plane
of body
• Adduction—moves a part toward median plane of body
 Circular movements
 Rotation and circumduction
• Rotation—pivoting a bone on its own axis
(Figure 9-15, D)
• Circumduction—moves a part so that its distal
end moves in a circle
 Supination and pronation (Figure 9-19, B)
• Supination—turns the hand palm side–up
• Pronation—turns the hand palm side–down
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Types and Range of Movement at Synovial Joints
 Gliding movements—simplest of all movements; articular surface of one bone
moves over articular surface of another without any angular or circular
movement
 Special movements
 Inversion and eversion (Figure 9-24, B)
• Inversion—turning sole of foot inward
• Eversion—turning sole of foot outward
 Protraction and retraction (Figure 9-16, B)
• Protraction—moves a part forward
• Retraction—moves a part backward
 Elevation and depression
• Elevation—moves a part up
• Depression—lowers a part
Cycle of Life: Articulations
 Bone development and the sequence of ossification between birth and skeletal
maturity affect joints
 Fontanels between cranial bones disappear
 Epiphysial plates ossify at maturity
 Older adults
 ROM decreases
 Changes in gait occur
 Skeletal diseases manifest as joint problems
 Abnormal bone growth (lipping)—influences joint motion
 Disease conditions can be associated with specific developmental periods
The Big Picture: Articulations
 Mobility of the upper extremity is extensive because of the following:
Arrangement of bones in shoulder girdle, arms, forearm, wrist, and hand
 Location and method of attachment of muscles to bones
 Proper functioning of joints
 Mobility and extensive ROM is needed to position the upper extremity and
hand to permit grasping and manipulation of objects, thus enabling effective
interaction with objects in external environment
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