Ch 8 Joints

Introduction to Joints (Articulations)

Joints, also known as articulations, are the sites where two or more bones meet. They play a crucial role in providing mobility to the skeleton while maintaining its structural integrity. Understanding the classification, structure, and function of joints is essential for comprehending movement and common joint-related disorders.

Key Vocabulary

• Joint (Articulation): The location where two bones meet.

• Synarthroses: Immovable joints.

• Amphiarthroses: Slightly movable joints.

• Diarthroses: Freely movable joints.

• Sutures, Syndesmoses, Gomphoses: Types of fibrous joints.

• Synchondroses, Symphyses: Types of cartilaginous joints.

• Synovial Joint: Joint characterized by a fluid-filled cavity.

• Articular Cartilage, Joint (Articular) Cavity, Articular Capsule, Synovial Membrane, Synovial Fluid: Structures associated with synovial joints.

• Ligaments: Bands of connective tissue that reinforce joints.

• Bursae, Tendon Sheath: Structures that reduce friction in joints.

• Flexion, Extension, Hyperextension, Abduction, Adduction, Circumduction, Rotation: Types of joint movements.

• Sprain, Dislocation (Luxation), Arthritis, Osteoarthritis, Rheumatoid Arthritis, Gouty Arthritis, Lyme Disease: Common joint injuries and disorders.

Classification of Joints

Structural Classification

Joints are classified structurally based on the material binding the bones and the presence or absence of a joint cavity.

• Fibrous Joints: Bones joined by dense fibrous connective tissue; no joint cavity. Examples: sutures, syndesmoses, gomphoses.

• Cartilaginous Joints: Bones united by cartilage; no joint cavity. Examples: synchondroses, symphyses.

• Synovial Joints: Bones separated by a fluid-filled joint cavity; most joints of the body are synovial and freely movable.

Functional Classification

Joints are also classified by the amount of movement they allow:

• Synarthroses: Immovable joints (e.g., sutures in the skull).

• Amphiarthroses: Slightly movable joints (e.g., intervertebral discs).

• Diarthroses: Freely movable joints (e.g., shoulder, knee).

Fibrous Joints

Types and Characteristics

• Sutures: Found only in the skull; bones are tightly bound by minimal fibrous tissue.

• Syndesmoses: Bones connected by ligaments; amount of movement depends on length of ligament.

• Gomphoses: Peg-in-socket joints; example: teeth in their sockets.

Cartilaginous Joints

Types and Characteristics

• Synchondroses: Bones united by hyaline cartilage; mostly immovable. Example: epiphyseal plates in children.

• Symphyses: Bones united by fibrocartilage; slightly movable. Example: pubic symphysis, intervertebral discs.

Synovial Joints

General Structure

• Articular Cartilage: Hyaline cartilage covering bone ends.

• Joint (Articular) Cavity: Space containing synovial fluid.

• Articular Capsule: Two-layered capsule enclosing the joint cavity.

• Synovial Fluid: Lubricates and nourishes articular cartilage.

• Reinforcing Ligaments: Strengthen and stabilize the joint.

• Nerves and Blood Vessels: Provide sensory input and nutrients.

Accessory Structures

• Bursae: Flattened sacs that reduce friction between tissues.

• Tendon Sheaths: Elongated bursae that wrap around tendons.

Movements at Synovial Joints

Types of Movements

• Gliding: One flat bone surface glides or slips over another.

• Angular Movements: Include flexion, extension, hyperextension, abduction, adduction, and circumduction.

• Rotation: Bone turns around its own long axis.

• Special Movements: Include supination, pronation, inversion, eversion, protraction, retraction, elevation, depression, opposition.

Types of Synovial Joints

Classification by Shape and Movement

• Plane Joints: Allow gliding movements (e.g., intercarpal joints).

• Hinge Joints: Permit flexion and extension (e.g., elbow).

• Pivot Joints: Allow rotation (e.g., proximal radioulnar joint).

• Condyloid Joints: Permit all angular movements (e.g., wrist).

• Saddle Joints: Allow greater freedom of movement (e.g., thumb).

• Ball-and-Socket Joints: Allow movement in all axes (e.g., shoulder, hip).

Joint Injuries and Disorders

Common Joint Injuries

• Sprain: Ligaments are stretched or torn.

• Dislocation (Luxation): Bones are forced out of alignment.

• Bursitis and Tendonitis: Inflammation of bursae or tendon sheaths.

Arthritis

• Osteoarthritis: Degenerative joint disease; most common in older adults.

• Rheumatoid Arthritis: Autoimmune disorder causing chronic inflammation.

• Gouty Arthritis: Caused by deposition of uric acid crystals in joints.

Lyme Disease

• Cause: Bacterial infection transmitted by ticks.

• Consequences: Can lead to joint pain and arthritis-like symptoms.

Summary Table: Types of Joints

Key Equations and Concepts

• Range of Motion: The degree to which a joint can move, determined by structure and ligaments.

• Stability vs. Mobility: Generally, the more mobile a joint, the less stable it is.

Additional info:

• For diagrams and more detailed structural features, refer to textbook figures and tables as indicated in the original study guide.

• Understanding joint classification is foundational for topics such as movement analysis, injury mechanisms, and treatment of joint disorders.