Biology Anatomy

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Karen Dunbar Kareiva

Ivy Tech Community College

Chapter 8 Part A

Joints

Why This Matters

Understanding the nature of joints will help you treat patients with injuries such as ankle sprains

8.1 Classification of Joints

Joints, also called articulations: sites where two or more bones meet

Functions of joints: give skeleton mobility and hold skeleton together

Two classifications:

Structural: three types based on what material binds the joints and whether a cavity is present

Fibrous

Cartilaginous

Synovial

8.1 Classification of Joints

Functional classifications: three types based on movement joint allows

Synarthroses: immovable joints

Amphiarthroses: slightly movable joints

Diarthroses: freely movable joints

Structural classifications are more clear cut, so these will be used here

8.2 Fibrous Joints

Bones joined by dense fibrous connective tissue

No joint cavity

Most are immovable

Depends on length of connective tissue fibers

Three types of fibrous joints

Sutures

Syndesmoses

Gomphoses

Sutures

Rigid, interlocking joints of skull

Allow for growth during youth

Contain short connective tissue fibers that allow for expansion

In middle age, sutures ossify and fuse

Immovable joints join skull into one unit that protects brain

Closed, immovable sutures referred to as synostoses

Figure 8.1a Fibrous joints.

Suture

Joint held together with very short,

interconnecting fibers, and bone

edges interlock. Found only in

the skull.

Suture

line

Fibrous

connective

tissue

Syndesmoses

Bones connected by ligaments, bands of fibrous tissue

Fiber length varies, so movement varies

Short fibers offer little to no movement

Example: inferior tibiofibular joint

Longer fibers offer a larger amount of movement

Example: interosseous membrane connecting radius and ulna

Figure 8.1b Fibrous joints.

Syndesmosis

Joint held together by a ligament.

Fibrous tissue can vary in length,

but is longer than in sutures.

Fibula

Tibia

Ligament

Gomphoses

Peg-in-socket joints

Only examples are the teeth in alveolar sockets

Fibrous connection is the periodontal ligament

Holds tooth in socket

Figure 8.1c Fibrous joints.

Gomphosis

“Peg in socket” fibrous joint.

Periodontal ligament holds tooth

in socket.

Socket of

alveolar

process

Root of

tooth

Periodontal

ligament

8.3 Cartilaginous Joints

Bones united by cartilage

Like fibrous joints, have no joint cavity

Not highly movable

Two types

Synchondroses

Symphyses

Synchondroses

Bar or plate of hyaline cartilage unites bones

Almost all are synarthrotic (immovable)

Examples

Temporary epiphyseal plate joints

Become synostoses after plate closure

Cartilage of 1st rib with manubrium of sternum

Figure 8.2a Cartilaginous joints.

Synchondroses

Bones united by hyaline cartilage

Sternum

(manubrium)

Epiphyseal

plate (temporary

hyaline cartilage

joint)

Joint between

first rib and

sternum

(immovable)

Symphyses

Fibrocartilage unites bone in symphysis joint

Hyaline cartilage also present as articular cartilage on bony surfaces

Symphyses are strong, amphiarthrotic (slightly movable) joints

Examples

Intervertebral joints

Pubic symphysis

Figure 8.2b Cartilaginous joints.

Symphyses

Bones united by fibrocartilage

Body of vertebra

Fibrocartilaginous

intervertebral disc

(sandwiched between

hyaline cartilage)

Pubic symphysis

8.4 Synovial Joints

Bones separated by fluid-filled joint cavity

All are diarthrotic (freely movable)

Include almost all limb joints

Characteristics of synovial joints

Have six general features

Have bursae and tendon sheaths associated with them

Stability is influenced by three factors

Allow several types of movements

Classified into six different types

General Structure

Synovial joints have six general features:

Articular cartilage: consists of hyaline cartilage covering ends of bones

Prevents crushing of bone ends

Joint (synovial) cavity: small, fluid-filled potential space that is unique to synovial joints

Articular (joint) capsule: two layers thick

External fibrous layer: dense irregular connective tissue

Inner synovial membrane: loose connective tissue that makes synovial fluid

General Structure (cont.)

Synovial fluid: viscous, slippery filtrate of plasma and hyaluronic acid

Lubricates and nourishes articular cartilage

Contains phagocytic cells to remove microbes and debris

Different types of reinforcing ligaments

Capsular: thickened part of fibrous layer

Extracapsular: outside the capsule

Intracapsular: deep to capsule; covered by synovial membrane

General Structure (cont.)

Nerves and blood vessels

Nerves detect pain; monitor joint position and stretch

Capillary beds supply filtrate for synovial fluid

Figure 8.3 General structure of a synovial joint.

Ligament

Joint cavity

(contains

synovial fluid)

Articular (hyaline)

cartilage

Fibrous

layer

Synovial

membrane

(secretes

synovial

fluid)

Periosteum

Articular

capsule

General Structure (cont.)

Other features of some synovial joints:

Fatty pads

For cushioning between fibrous layer of capsule and synovial membrane or bone

Articular discs (menisci)

Fibrocartilage separates articular surfaces to improve “fit” of bone ends, stabilize joint, and reduce wear and tear

Bursae and Tendon Sheaths

Bags of synovial fluid that act as lubricating “ball bearing”

Not strictly part of synovial joints, but closely associated

Bursae: reduce friction where ligaments, muscles, skin, tendons, or bones rub together

Tendon sheaths: elongated bursae wrapped completely around tendons subjected to friction

Figure 8.4a Bursae and tendon sheaths.

Acromion

of scapula

Subacromial

bursa

Fibrous layer of

articular capsule

Joint cavity

containing

synovial fluid

Articular

cartilage

Tendon

sheath

Synovial

membrane

Tendon of

long head

of biceps

brachii muscle

Fibrous

layer

Humerus

Frontal section through the right shoulder joint

Figure 8.4b Bursae and tendon sheaths.

Bursa rolls

and lessens

friction.

Humerus head

rolls medially

as arm abducts.

Humerus moving

Enlargement of (a), showing how

a bursa eliminates friction where

a ligament (or other structure) would

rub against a bone

Factors Influencing Stability of Synovial Joints

Three factors determine stability of joints to prevent dislocations:

Shape of articular surface (minor role)

Shallow surfaces less stable than ball-and-socket

Ligament number and location (limited role)

The more ligaments, the stronger the joint

Muscle tone keeps tendons taut as they cross joints (most important)

Extremely important in reinforcing shoulder and knee joints and arches of the foot

Table 8.2-1 Structural and Functional Characteristics of Body Joints

Table 8.2-2 Structural and Functional Characteristics of Body Joints (continued)

Table 8.2-3 Structural and Functional Characteristics of Body Joints (continued)

Movements Allowed by Synovial Joints

All muscles attach to bone or connective tissue at no fewer than two points

Origin: attachment to immovable bone

Insertion: attachment to movable bone

Muscle contraction causes insertion to move toward origin

Movements occur along transverse, frontal, or sagittal planes

Movements Allowed by Synovial Joints (cont.)

Range of motion allowed by synovial joints

Nonaxial: slipping movements only

Uniaxial: movement in one plane

Biaxial: movement in two planes

Multiaxial: movement in or around all three planes

Three general types of movements

Gliding

Angular movements

Rotation

Movements Allowed by Synovial Joints (cont.)

Gliding movements

One flat bone surface glides or slips over another similar surface

Examples

Intercarpal joints

Intertarsal joints

Between articular processes of vertebrae

Figure 8.5a Movements allowed by synovial joints.

Gliding

Gliding movements at the wrist

Movements Allowed by Synovial Joints (cont.)

Angular movements

Increase or decrease angle between two bones

Movement along sagittal plane

Angular movements include:

Flexion: decreases the angle of the joint

Extension: increases the angle of the joint

Hyperextension: movement beyond the anatomical position

Figure 8.5b Movements allowed by synovial joints.

Hyperextension

Extension

Flexion

Angular movements: flexion,

extension, and hyperextension

of the neck

Figure 8.5c Movements allowed by synovial joints.

Extension

Hyperextension

Flexion

Angular movements: flexion,

extension, and hyperextension of

the vertebral column

Figure 8.5d Movements allowed by synovial joints.

Flexion

Hyper-

extension

Extension

Flexion

Extension

Angular movements: flexion, extension, and hyperextension at the shoulder and knee

Movements Allowed by Synovial Joints (cont.)

Angular movements (cont.)

Abduction: movement along frontal plane, away from the midline

Adduction: movement along frontal plane, toward the midline

Circumduction

Involves flexion, abduction, extension, and adduction of limb

Limb describes cone in space

Figure 8.5e Movements allowed by synovial joints.

Abduction

Adduction

Circumduction

Angular movements: abduction, adduction, and

circumduction of the upper limb at the shoulder

Movements Allowed by Synovial Joints (cont.)

Rotation: turning of bone around its own long axis, toward midline or away from it

Medial: rotation toward midline

Lateral: rotation away from midline

Examples

Rotation between C1 and C2 vertebrae

Rotation of humerus and femur

Figure 8.5f Movements allowed by synovial joints.

Rotation

Lateral

rotation

Medial

rotation

Rotation of the head, neck, and lower limb

Movements Allowed by Synovial Joints (cont.)

Special movements

Supination and pronation: rotation of radius and ulna

Supination: palms face anteriorly

Radius and ulna are parallel

Pronation: palms face posteriorly

Radius rotates over ulna

Dorsiflexion and plantar flexion of foot

Dorsiflexion: bending foot toward shin

Plantar flexion: pointing toes

Figure 8.6a Special body movements.

Pronation

(radius rotates

over ulna)

Supination

(radius and ulna

are parallel)

Pronation (P) and supination (S)

Figure 8.6b Special body movements.

Dorsiflexion

Plantar flexion

Dorsiflexion and plantar flexion

Movements Allowed by Synovial Joints (cont.)

Special movements (cont.)

Inversion and eversion of foot

Inversion: sole of foot faces medially

Eversion: sole of foot faces laterally

Protraction and retraction: movement in lateral plane

Protraction: mandible juts out

Retraction: mandible is pulled toward neck

Figure 8.6c Special body movements.

Inversion

Eversion

Inversion and eversion

Figure 8.6d Special body movements.

Protraction

of mandible

Retraction

of mandible

Protraction and retraction

Movements Allowed by Synovial Joints (cont.)

Special movements (cont.)

Elevation and depression of mandible

Elevation: lifting body part superiorly

Example: shrugging shoulders

Depression: lowering body part

Example: opening jaw

Opposition: movement of thumb

Example: touching thumb to tips of other fingers on same hand or any grasping movement

Figure 8.6e Special body movements.

Elevation

of mandible

Depression

of mandible

Elevation and depression

Figure 8.6f Special body movements.

Opposition

Types of Synovial Joints

There are six different types of synovial joints

Categories are based on shape of articular \

surface, as well as movement joint is capable of

Plane

Hinge

Pivot

Condylar

Saddle

Ball-and-socket

Focus Figure 8.1a Six types of synovial joint shapes determine the movements that can occur at a joint.

Plane joint

Nonaxial movement

Meta-

carpals

Carpals

Flat

articular

surfaces

Gliding

Examples: Intercarpal joints, intertarsal joints, joints between

vertebral articular surfaces

Focus Figure 8.1b Six types of synovial joint shapes determine the movements that can occur at a joint.

Hinge joint

Humerus

Cylinder

Trough

Uniaxial movement

Medial/lateral

axis

Ulna

Flexion and extension

Examples: Elbow joints, interphalangeal joints

Focus Figure 8.1c Six types of synovial joint shapes determine the movements that can occur at a joint.

Pivot joint

Uniaxial movement

Sleeve

(bone and

ligament)

Vertical axis

Ulna

Radius

Axle (rounded

bone)

Rotation

Examples: Proximal radioulnar joints, atlantoaxial joint

Focus Figure 8.1d Six types of synovial joint shapes determine the movements that can occur at a joint.

Condylar joint

Phalanges

Medial/

lateral

axis

Oval

articular

surfaces

Biaxial movement

Anterior/

posterior

axis

Meta-

carpals

Flexion

and extension

Adduction

and abduction

Examples: Metacarpophalangeal (knuckle) joints, wrist joints

Focus Figure 8.1e Six types of synovial joint shapes determine the movements that can occur at a joint.

Saddle joint

Anterior/

posterior

axis

Metacarpal

Articular

surfaces

are both

concave

and convex

Biaxial movement

Medial/

lateral

axis

Adduction

and abduction

Flexion and

extension

Trapezium

Example: Carpometacarpal joints of the thumbs

Focus Figure 8.1f Six types of synovial joint shapes determine the movements that can occur at a joint.

Ball-and-socket joint

Multiaxial movement

Anterior/posterior

axis

Cup

(socket)

Medial/lateral

axis

Scapula

Spherical

head

(ball)

Humerus

Flexion

and extension

Adduction and

abduction

Rotation

Examples: Shoulder joints and hip joints

Vertical

axis