Chapter 9
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
Classification of Joints
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)
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
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
Representative Synovial Joints
Vertebral joints (Figures 9-13 and 9-14)
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
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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