8-1

Articulations or Joints

• Articulation or Joint– Place where two bones (or bone and cartilage)

come together

• Arthrology = study of the joints• Functions of joints

– Give the skeleton mobility– Hold the skeleton together

• Structure correlated with movement

8-2

Classification of Joints• Structural classes: based on type

of connective tissue type that binds bones and whether or not a joint cavity is present– Fibrous– Cartilaginous– Synovial

• Functional classes: based on degree of motion – Synarthrosis: non-movable– Amphiarthrosis: slightly movable– Diarthrosis: freely movable

8-3

Fibrous Joints

• Characteristics– United by fibrous connective tissue– Have no joint cavity– Move little or none

• Types: – Sutures– Syndesmoses

8-4

Fibrous Joints: Syndesmoses

• Two bones joined by ligament

• Most moveable of fibrous joints

• Examples: radioulnar joint and tibiofibular joints

8-5

Cartilaginous Joints

• Bones are joined by cartilage

• Lack a joint cavity

• Types– Synchondroses: bound by hyaline cartilage

– Symphyses: bound by fibrocartilage

8-6

Cartilaginous Joints: Synchondroses

• Joined by hyaline cartilage

• Little or no movement• Some are temporary and are replaced by synostoses

• Some are permanent• Some like costochondral joints develop into synovial joints

• Examples: Epiphyseal plates, 1st sternocostal

8-7

Cartilaginous Joints: Symphyses

• Fibrocartilage uniting two bones

• Slightly movable• Examples: symphysis pubis, between the manubrium and the body of the sternum, intervertebral disks.

8-8

Synovial Joints

• Contain synovial fluid in a joint cavity called the synovial cavity

• Allow considerable movement (diarthroses)

• Most joints that unite bones of appendicular skeleton reflecting greater mobility of appendicular skeleton compared to axial

8-9

Structure of

Synovial Joints

• Articular cartilage: – Hyaline cartilage that covers

epiphysis– Absorbs compression of joint

• Joint cavity (synovial cavity)– Unique to synovial joints– Cavity is a potential space

that holds small amount of fluid

• Synovial fluid: – Viscous fluid similar to raw

egg white– A filtrate of blood from

capillaries in synovial membrane

– Contains glycoprotein molecules secre-ted by fibroblasts

• Nerves in capsule help brain know position of joints (proprioception)

8-10

Flexion and Extension• Flexion: movement of a body part anterior or posterior to the coronal plane

• Extension: movement of a body part posterior or anterior to the coronal plane

• Dorsoflexion - foot lifted toward the shin• Plantar flexion - pointing toes downward• Abduction: movement away from the midline• Adduction: movement toward the midline

8-11

Types of Synovial Joints:Plane Joints• Plane or gliding

joints– Monaxial. One flat bone surface glides or slips over another similar surface

– Sometimes considered an amphiarthrosis

– Examples: intervertebral, intercarpal, intertarsal acromioclavicular, carpometacarpal, tarsometatarsal,

8-12

Hinge and Pivot Joints• Hinge joints

– Monaxial– Convex cylinder in one bone; corresponding concavity in the other

– Example: elbow, ankle, interphalangeal

• Pivot joints– Monaxial. Rotation around a single axis.

– Cylindrical bony process rotating within a circle of bone and ligament

– Example: articulation between dens of axis and atlas (atlantoaxial), proximal radioulnar

8-13

Saddle joints• Each articular surface is shaped like a saddle; • Trapeziometacarpal joint at base of the thumb

Types of Synovial Joints:

8-14

Ball-and-Socket and Ellipsoid Joints

• Ball-and-socket– Smooth heispherical head fits within a cuplike depression

– Multiaxial– Examples: shoulder and hip joints

• Condyloid (ellipsoid) joint– Oval convex surface on one bone fits into a similarly shaped depression on the next• Atlantooccipital joint (C1-C2)• Metacarpophalangeal joints

8-15

The Knee Joint• Most complex diarthrosis

– patellofemoral = gliding joint– tibiofemoral = gliding with slight rotation and gliding possible in flexed position

• Joint capsule anteriorly consists of patella and extensions of quadriceps femoris tendon

• Capsule strengthened by extracapsular and intracapsular ligaments

8-16

Effects of Aging on Joints

• Tissue repair slows; rate of new blood vessel development decreases

• Articular cartilages wear down and matrix becomes more rigid

• Production of synovial fluid declines• Ligaments and tendons become shorter and less flexible: decrease in range of motion (ROM)

• Muscles around joints weaken• A decrease in activity causes less flexibility and decreased ROM