Chapter 8: Articulations and Joints – Study Guide

Articulations (Joints)

Definition of Articulation

An articulation (or joint) is the location where two or more bones meet. Joints allow for varying degrees of movement and provide structural support to the skeleton.

Functional Classifications of Joints

Overview

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

• Synarthroses: Immovable joints

• Amphiarthroses: Slightly movable joints

• Diarthroses: Freely movable joints

Synarthroses

• Permit no movement between bones.

• Examples: Sutures of the skull.

Amphiarthroses

• Allow slight movement.

• Examples: Intervertebral discs, pubic symphysis.

Diarthroses

• Freely movable joints.

• Examples: Shoulder, knee, hip joints.

Structural Classifications of Joints

Overview

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

• Fibrous Joints

• Cartilaginous Joints

• Synovial Joints

Fibrous Joints

Formed by dense connective tissue; bones are joined by collagen fibers. These joints are generally immovable.

• Sutures: Found only in the skull; bones interlock and are bound by short connective tissue fibers.

• Syndesmoses: Bones connected by ligaments; allow more movement than sutures but still limited (e.g., distal tibiofibular joint).

• Gomphoses: Peg-in-socket joints; found where teeth fit into alveolar sockets of the jaw.

Cartilaginous Joints

Bones are united by cartilage; no joint cavity is present. These joints allow little to no movement.

• Synchondroses: Bones united by hyaline cartilage (e.g., epiphyseal plates in children, joint between first rib and sternum).

• Symphyses: Bones joined by fibrocartilage; provide strength with flexibility (e.g., intervertebral discs, pubic symphysis).

Synovial Joints

Most common and movable type of joint in the body. Bones are separated by a fluid-filled joint cavity.

• Articular Surfaces: Smooth surfaces of bones at the joint, covered with articular cartilage to reduce friction.

• Bursae: Fluid-filled sacs that reduce friction between moving structures (e.g., tendons and bones).

• Tendon Sheaths: Elongated bursae that wrap around tendons to reduce friction.

• Stabilizing Factors: Include the shape of articular surfaces, ligaments, and muscle tone.

Six Major Features of Synovial Joints

1. Articular cartilage

2. Joint (synovial) cavity

3. Articular capsule

4. Synovial fluid

5. Reinforcing ligaments

6. Nerves and blood vessels

General Movement Types

• Gliding

• Angular movements (flexion, extension, etc.)

• Rotation

Movements of Synovial Joints

• Zero position: Anatomical position, reference for joint movements.

• Flexion: Decreases the angle between bones (e.g., bending the elbow).

• Extension: Increases the angle between bones (e.g., straightening the knee).

• Hyperextension: Extension beyond the anatomical position.

• Abduction: Movement away from the midline.

• Adduction: Movement toward the midline.

• Elevation: Lifting a body part superiorly (e.g., shrugging shoulders).

• Depression: Moving a body part inferiorly.

• Protraction: Moving a body part anteriorly (e.g., jutting jaw forward).

• Retraction: Moving a body part posteriorly.

• Circumduction: Circular movement combining flexion, extension, abduction, and adduction.

• Rotation: Turning a bone around its own long axis.

• Supination: Rotating the forearm so the palm faces up.

• Pronation: Rotating the forearm so the palm faces down.

• Dorsiflexion: Lifting the foot upward toward the shin.

• Plantar flexion: Pointing the toes downward.

• Opposition: Movement of the thumb to touch the fingertips.

Joint Injuries and Disorders

Common Joint Injuries

• Cartilage tears: Often due to compression and shear stress; may require surgical repair.

• Sprains: Ligaments are stretched or torn.

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

• Subluxation: Partial dislocation of a joint.

• Bursitis: Inflammation of a bursa, usually caused by a blow or friction.

• Tendonitis: Inflammation of tendon sheaths, typically caused by overuse.

Arthritis

• General term for inflammatory or degenerative diseases of joints.

• Common types include:

  • Osteoarthritis: Degenerative joint disease, often related to aging.

  • Rheumatoid arthritis: Autoimmune disorder causing chronic inflammation.

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

RICE Method for Joint Injuries

• Rest: Avoid using the injured joint to prevent further damage.

• Ice: Apply ice to reduce swelling and pain.

• Compression: Use an elastic bandage to minimize swelling.

• Elevation: Raise the injured joint above heart level to reduce swelling.

Example: A sprained ankle is commonly treated with the RICE method to promote healing and reduce inflammation.

Additional info: Synovial joints are the most common type of joint in the body and are essential for most voluntary movements. Proper joint health is crucial for mobility and quality of life.