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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