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
l Fibrous
l Cartilaginous
l Synovial
• Mobility
l Immovable (synarthroses)
l Slightly movable (amphiarthroses)
l 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
l Skull sutures
l 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
l Tibiofibular joint (ligament)
l Pubic symphysis
l Intervertebral joints
l Symphysis are joints held together by fibrocartilage (Fig 8.1 & 8.2)
Freely Moveable Joints
• Also referred to as Synovial joints
• Allow a wide degree and range of movement
Synovial Joint
• Articular surface
l Lined by hyaline cartilage
• Joint cavity
l Space between bones that make up the joint
• Articular capsule
l Membrane that surrounds the joint cavity
l Outer fibrous capsule is continuous with the periosteum (dense irregular CT)
l Inner synovial membrane (loose CT)
• Synovial fluid
l Fluid that fills the joint cavity
l Functions to reduce friction between the cartilaginous articulating surface
• Reinforcing ligaments
l Fibrous bands that link one bone to another
l Cannot tolerate movement beyond the normal range of motion (Fig 8.3)
Movements Allowed by Synovial Joints
• Gliding
l Occurs when one bone slips over another
l Linear motion is very slight and may occur in any direction
l Occurs at the intercarpal, intertarsal and sternoclavicular joints
• Angular
l Flexion
l Bending movement along the saggital plane
l Joint angle decreases
l Extension
l Opposite of flexion
l Hyperextension
l Extension beyond the anatomical position
l Abduction
l Movement of a limb away from the midline
l Adduction
l Opposite of abduction
l Circumduction
l Limb movement that describes a cone in space
l Rotation
l Turning a bone around its long axis (Fig 8.5 a – g; Fig 8.6 a-e)
Types of Synovial Joints
• Plane joints
l Flattened or slightly curved articular surfaces that allow gliding movement e.g. intercarpal, intertarsal
• Hinge joints
l Allows angular motion in one plane e.g. elbow, knee, ankle
• Pivot joints
l Allows uniaxial rotation of a bone along its long axis e.g. atlas on the axis, proximal radioulnar joint (Fig 8.7)
• Condyloid joints
l Allows angular motion in two planes and circumduction e. g. radiocarpal, metacarpophalangeal
• Saddle joint
l Allows angular motion in two planes and circumduction e.g. carpometacarpal joint at the base of the thumb
• Ball and socket
l Allows a variety of angular and rotational movement e.g. shoulder, hip