Joints
Sites where two or more bones meet
Except the hyoid bone, all other bones articulate with at least one other bone
Give mobility to the skeleton and hold the skeleton together
They are the weakest parts of the skeleton though they can resist various forces that
threaten their configuration
Classification of Joints
Structure
Fibrous
Cartilaginous
Synovial
Mobility
Immovable (synarthroses)
Slightly movable (amphiarthroses)
Freely movable (diarthroses)
Immovable Joints
Do not allow any form of movement
Held together by fibrous connective tissue or cartilage
Bones actually fuse over time
Examples:
Skull sutures
Epiphyseal plate
Slightly Movable Joints
Allow a small degree of movement that is dependent on the connecting fiber
length or arrangement
Held together by fibrous connective tissue or cartilage and sometimes ligaments
Examples
Tibiofibular joint (ligament)
Pubic symphysis
Intervertebral joints
Symphysis are joints held together by fibrocartilage
Freely Moveable Joints
Also referred to as Synovial joints
Allow a wide degree and range of movement
Synovial Joint
Articular surface
Lined by hyaline cartilage
Joint cavity
Space between bones that make up the joint
Articular capsule
Membrane that surrounds the joint cavity
Outer fibrous capsule is continuous with the periosteum (dense irregular CT)
Inner synovial membrane (loose CT)
Synovial fluid
Fluid that fills the joint cavity
Functions to reduce friction between the cartilaginous articulating surface
Reinforcing ligaments
Fibrous bands that link one bone to another
Cannot tolerate movement beyond the normal range of motion
Movements Allowed by Synovial Joints
Gliding
Occurs when one bone slips over another
Linear motion is very slight and may occur in any direction
Occurs at the intercarpal, intertarsal and sternoclavicular joints
Angular
Flexion
Bending movement along the saggital plane
Joint angle decreases
Extension
Opposite of flexion
Hyperextension
Extension beyond the anatomical position
Abduction
Movement of a limb away from the midline
Adduction
Opposite of abduction
Circumduction
Limb movement that describes a cone in space
Rotation
Turning a bone around its long axis
Types of Synovial Joints
Plane joints
Flattened or slightly curved articular surfaces that allow gliding movement
e.g. intercarpal, intertarsal
Hinge joints
Allows angular motion in one plane e.g. elbow, knee, ankle
Pivot joints
Allows uniaxial rotation of a bone along its long axis e.g. atlas on the axis,
proximal radioulnar joint
Condyloid joints
Allows angular motion in two planes and circumduction e. g. radiocarpal,
metacarpophalangeal
Saddle joint
Allows angular motion in two planes and circumduction e.g.
carpometacarpal joint at the base of the thumb
Ball and socket
Allows a variety of angular and rotational movement e.g. shoulder, hip