Articulations

A Classification of Joints

Articulations

• Articulations

• Where two bones interconnect

• Immovable joints

• Synarthroses, or bony

• Slightly moveable joints

• Amphiarthroses, or fibrous / cartilagenous

• Freely moveable joints

• Diarthroses, or synovial

Synarthroses (immovable joints)

• Four major types

• Suture = skull bones bound together by dense connective tissue

• Gomphosis = teeth bound to bony sockets by periodontal ligaments

• Synchondrosis = two bones bound by rigid cartilaginous bridge

• Syntosis = two bones completely fused

Amphiarthroses (slightly movable joints)

• Two major types

• Syndesmosis = bones connected by a ligament

• Symphysis = bone separated by fibrocartilage

Diarthroses (freely movable joints)

• Bony surfaces enclosed within articular capsule

• Bony surfaces covered by articular cartilage

• Bony surfaces lubricated by synovial fluid

• Structures include

• Menisci

• Fat pads

• Accessory ligaments

• Bursae

Articular Form and Function

Dynamic motion

• Dynamic motion

• Linear motion

• Angular motion

• Rotation

• Joints classified based on type of motion permitted

• Monaxial

• Biaxial

• Triaxial

Types of movement

• Gliding motion

• Two surfaces slide past one another

• Angular motion

• Flexion, extension, hyperextension

• Abduction, adduction

• Circumduction

Rotational movement

• Left or right

• Medial (internal) or lateral (external)

• Pronation or supination in the bones of the forearm only

Special movement

• Movements of the foot

• Inversion and eversion

• Plantar flexion and dorsiflexion

• Movements of the thumb

• Opposition

Other movements

• Protraction moves a structure anteriorly

• Retraction moves a structure posteriorly

• Elevation moves a structure superiorly

• Depression moves a structure inferiorly

• Lateral flexion bends the vertebrae to one side

Structural classification of joints

• Gliding joints permit movement in a single plane

• Hinge joints are monaxial joints permitting angular motion in one plane

• Pivot joints are monaxial joints that permit rotation

• Ellipsoid joints are biaxial joints that pit one bone in an oval depression of another

• Saddle joints are biaxial joints with one concave and one convex bone face

• Ball-and-socket joints are triaxial joints that permit rotation and other movements

Representative Articulations

Intervertebral articulations

• Gliding joints

• Vertebral bodies form symphyseal joints cushioned by intervertebral discs

• Outer anulus fibrosus and inner nucleus pulposus

• Stabilized by ligaments

Shoulder joint (glenohumoral joint)

• Glenoid cavity and head of humerus

• Ball and socket diarthroses

• Stabilized by ligaments

• Strength and stability sacrificed for range of motion

The elbow joint

• Permits only flexion and extension

• Hinge diarthroses

• Reinforced with strong ligaments

Hip joint

• Ball and socket diarthroses

• Acetabulum and head of femur

• Permits flexion/extension, abduction/ adduction, circumduction, rotation

• Stabilized by numerous ligaments

Knee joint

• Hinge joint with incomplete articular capsule

• Formed by the condyles of the femur and the condylar surfaces of the tibia

• Accessory structures help stabilize lateral movements

• Permits flexion/extension, limited rotation

• Supported by ligaments

Aging and Articulations

Joint problems with aging

• Joint problems associated with aging

• Relatively common

• Rheumatism – general term for pain and stiffness in muscular and skeletal elements

• Arthritis – all rheumatic diseases affecting synovial joints

Bones and Muscles

Musculoskeletal system

• Encompasses the extensive interactions between the muscular and skeletal systems