Comprehensive Joint Study Notes

Articular Cartilage

• Covers articulating surfaces.

• Type: Hyaline cartilage.

• Reduces friction and provides shock absorption.

Joints (Articulations)

• Definition: Where two bones meet.

• Connected by cartilage, ligaments, and synovial membranes.

• Location of body movement.

• Axis of motion:

  • Monoaxial: 1 direction.

  • Biaxial: 2 directions.

  • Triaxial: 3 directions.

Two Classification Schemes

• Structural: Based on the type of tissue connecting the bones.

• Functional: Based on the range of motion.

Joint Structure and Function

• Joint structure determines its function.

Clinical Relevance

• Dislocation: Joint goes out of place.

• Sprain: Ligaments are overstretched or broken.

• Arthritis: Inflammation of the joint.

Structural Classifications

• Fibrous: Connected by dense connective tissue; little to no movement.

• Cartilaginous: Connected by cartilage; slight mobility.

• Bony (Synostoses): Fused together, no movement.

• Synovial: Freely movable; contain synovial fluid.

Functional Classifications

• Synarthrosis (Immovable Joint):

  • Examples: Sutures of the skull and teeth sockets (gomphoses).

• Amphiarthrosis (Slightly Movable Joint):

  • Examples: Pubic symphysis and intervertebral discs.

• Diarthrosis (Freely Movable Joints):

  • Located at the ends of long bones.

  • Surrounded by a joint capsule (articular capsule) made of two layers:

    • Fibrous (outer layer).

    • Inner synovial membrane (contains synovial fluid).

  • Examples: Shoulder, elbow, ankle.

Focus on functional classifications for the exam!

Components of Synovial Joints

• Fibrous joint capsule (outer layer).

• Articular cartilage and synovial membrane (inner layer).

• Synovitis: Infection in the synovial fluid.

Synovial Fluid

• Consistency: Similar to egg yolk → viscous (thick).

• Functions: Reduces friction, provides nutrients, and absorbs shock.

• Contains proteoglycans (\rightarrow) proteo = protein and glycan = sugars.

• Glycosaminoglycans: Hyaluronic acid \rightarrow essential for lubrication and shock absorption.

• Compared to synarthrosis and amphiarthrosis, diarthrosis (synovial joints) are weaker but highly movable.

• Stabilized by accessory structures:

  • Cartilages and fat pads.

  • Ligaments.

  • Tendons.

  • Bursae.

Cartilages

• Meniscus (Menisci): Fibrocartilage pad between opposing bones.

• Functions: Reduces friction and absorbs shock.

Fat Pads

• Adipose tissue covered by synovial membrane.

• Function: Provides padding and cushioning.

Ligaments

• Connect bone to bone.

• Support and strengthen joints.

• Sprain: When a ligament is stretched or torn:

  • Grade 1: Mild sprain.

  • Grade 2: Moderate sprain.

  • Grade 3: Severe sprain.

Tendons

• Connect bone to muscle.

• Attach muscles around the joint.

Bursae

• Small pockets of synovial fluid.

• Functions:

  • Reduce friction.

  • Protect ligaments and muscles from wear and tear.

  • Bursitis: Inflammation of the bursae.

Arthritis

• Rheumatoid Arthritis (RA): Autoimmune (genetic).

• Osteoarthritis (OA): Aging-related.

Movements at Synovial Joints

• Monoaxial: 1 plane (e.g., elbow) \rightarrow Hinge joint \rightarrow Flexion and extension.

• Biaxial: 2 planes (e.g., wrist) \rightarrow Condyloid joint \rightarrow Flexion, extension, and side-to-side movement.

• Triaxial → 3 planes ( e.g. shoulder) → ball and socket joint → flexion, extension,

• extension, abduction, adduction, and internal/external rotation.

Types of Movement

• Gliding Movement: Flat surfaces glide past each other \rightarrow Wrist and ankle.

• Angular Movement: Changes the angle between bones \rightarrow Flexion, extension, abduction, adduction.

• Circumduction: Circular movement \rightarrow Shoulder.

• Rotational Movement: Medial and lateral rotation, pronation and supination of the forearm.

• Special Movements:

  • Elevation

  • Depression

  • Inversion

  • Eversion

  • Protraction

  • Retraction

  • Opposition

  • Dorsiflexion

  • Plantarflexion