Fundamentals of Anatomy and Physiology: Articulations

Joints - Articulations

• Definition: Areas where two bones meet.

• Terminology:

  • arthro- = joint

  • arthritis is = inflammation of a joint

  • arthroplasty = surgical repair of a joint or joint replacement

• Alternate Name: Articulations.

• Structure and Movement: Joint structure determines movement; there is a compromise between strength and movement.

• Classification:

  • By Function (range of motion)

  • By Structure

Classification of Joints by Function

• Types of Joints:

  1. Synarthrosis:

  • Immovable joints.

  • Examples: sutures in skull, epiphyseal lines.

  1. Amphiarthrosis:

  • Slightly movable joints.

  • Examples: intervertebral discs, pubic symphysis.

  1. Diarthrosis:

  • Freely movable joints (all are synovial joints).

  • Examples: knee, shoulder, hip.

Classification of Joints by Structure

• Types of Joints:

  • Bony Joints:

  • Two bones fuse, and the boundary disappears.

  • Examples: frontal bone, mandible.

  • Fibrous Joints:

  • Bones are held by dense fibrous tissue.

  • Types:

    • Suture: Occurs in the skull, irregular edges add strength.

    • Gomphosis: Tooth in bony socket.

  • Cartilaginous Joints:

  • Bones connect via cartilage.

  • Examples: epiphyseal plate, sternocostal joints.

  • Synovial Joints:

  • Bones are separated by synovial fluid.

  • Examples: shoulder, knee.

Synarthroses - Joints with No Movement

• Types:

  • Bony Joint (Synostosis):

  • Example: fusion of the frontal bone.

  • Fibrous Joints:

  • Suture:

    • Only between skull bones.

    • Irregular edges for strength.

  • Gomphosis:

    • Tooth into the alveolar socket.

  • Cartilaginous Joints (Synchondrosis):

  • Example: epiphyseal plate.

Amphiarthroses - Joints with Slight Movement

• Fibrous Joints (Syndesmosis):

  • Opposing surfaces united by ligament or interosseous membrane.

  • Example: between the radius and ulna.

• Cartilaginous Joints (Symphysis):

  • Bones are separated by a fibrocartilage pad.

Synovial Joints - Characteristics

• Definition: Articulating bones separated by synovial fluid.

• Movement Classification:

  • Nonaxial: Movement in any direction (gliding).

  • Monaxial: Movement in one plane (hinge; pivot).

  • Biaxial: Movement in two planes (condylar; saddle).

  • Triaxial: Movement in three planes (ball-and-socket).

Structure of Synovial Joints

• Joint Capsule:

  • The outer fibrous layer joins the periosteum.

  • Inner synovial membrane secretes synovial fluid.

• Articular Surface:

  • Lined with hyaline cartilage for lubrication.

  • Damage increases friction.

Synovial Fluid

• Texture similar to raw egg white.

• Functions:

  • Lubrication

  • Shock absorption

  • Nutrient distribution

  • Waste removal by macrophages.

Accessory Structures in Synovial Joints

• Cartilages & Fat Pads:

  • Meniscus: Absorbs shock and stabilizes.

  • Fat Pads: Fill the spaces during movement.

• Ligaments:

  • Avascular, dense, regular connective tissue for joint stability.

• Tendons:

  • Connect the muscle to the bone.

• Bursae:

  • Reduces friction, provides shock absorption.

Stability Factors in Synovial Joints

• Stabilization by:

  • Collagen fibers

  • Menisci and fat pads

  • Other bones or muscles

  • Tension in associated tendons.

Intervertebral Joints

• Types:

  • Amphiarthrosis: Symphysis with fibrocartilaginous discs.

  • Diarthrosis: Hinge joint (skull with atlas), pivot (atlas and axis), gliding.

• Movements:

  • Flexion, extension, lateral flexion, rotation.

Knee Joint

• Type of Articulation: Diarthrosis (hinge joint).

• Movements:

  • Flexion, extension, and limited rotation.

• Accessory Structures:

  • Menisci (medial and lateral).

  • Ligaments (ACL, PCL, collateral ligaments).

Shoulder Joint

• Type of Articulation: Diarthrosis (ball-and-socket).

• Movements:

  • Flexion, extension, abduction, adduction, circumduction, rotation.

• Accessory Structures:

  • Glenoid labrum, major ligaments, rotator cuff.

Hip Joint

• Type of Articulation: Diarthrosis (ball-and-socket).

• Movements:

  • Flexion, extension, abduction, adduction, rotation.

• Accessory Structures:

  • Acetabular labrum, multiple ligaments (iliopsoas, pubofemoral, ischiofemoral).