Topic 5 Joints

Joints Overview

• Definition: Joints, or articulations, are locations where bones meet, including connections to cartilage and teeth.

• Stability: Joints vary in stability; some are very stable while others allow more movement.

Classification of Joints

By Structure

• Fibrous Joints:

  • Joined by collagen fibres (dense regular connective tissue).

  • No joint cavity; mostly immovable.

• Cartilaginous Joints:

  • Bones attached by cartilage; no joint cavity.

  • Generally immovable or slightly mobile.

• Synovial Joints:

  • Articulating bones separated by a fluid-filled joint cavity.

  • most joins are synovial

  • Freely mobile (diarthroses).

By Function

• Synarthrosis: Immobile joints.

• Amphiarthrosis: Slightly movable joints.

• Diarthrosis: Freely movable joints.

Types of Joints

Fibrous Joints

• Suture: Interlocking seams (e.g., cranial bones); immovable.

• Syndesmosis: Connected by ligaments; allows some movement (e.g., tibiofibular joint).

  • long ligaments = more movements; ex. interosseous membrane

  • short ligaments = less movements; ex.tibiofibular membrane

• Gomphosis: Peg-in-socket joint (e.g., teeth in sockets); immobile.

  • periodontal ligament

Cartilaginous Joints

• Synchondrosis: Bones joined by hyaline cartilage (e.g., joint between the first rib and sternum); immovable.

• Symphysis: Bones joined by fibrocartilage (e.g., intervertebral discs); slightly movable.

  • amphiarthorotic

Synovial Joints

• Characterized by:

  • Articular cartilage (hyaline).

  • Joint cavity containing synovial fluid.

  • Articular capsule enclosing the joint with an outer fibrous layer and inner synovial membrane.

    • outer fibrous layer (dense irregular connective tissue); continuous with periosteum

    • inner synovial membrane (special loose connection tissue); secrets synovial fluid

• Ligaments: Connect bones and provide stability; includes sensory nerves and blood vessels.

• Sensory nerves: detect pain and amount of stretch in a joint

• Blood vessels: nourish tissues in the joint

Accessory Structures in Synovial Joints

• Bursa: Sacs that reduce friction, contain synovial membrane and fluid.

• Tendon Sheath: Elongated bursa surrounding tendons.

Types of Synovial Joints

• Plane Joint: Nonaxial movement; gliding (e.g., intercarpal joints).

• Hinge Joint: Uniaxial movement (e.g., elbow).

• Pivot Joint: Uniaxial rotation (e.g., proximal radioulnar joint).

• Condylar Joint: Biaxial movement (e.g., metacarpophalangeal joints).

• Saddle Joint: Biaxial movement with concave and convex surfaces (e.g., thumb joint).

• Ball-and-Socket Joint: Multiaxial movement (e.g., shoulder and hip joints).

Movements Allowed by Synovial Joints

1. Gliding Motion

• Occurs mainly in plane joints.

• Example: Movement between carpals.

2. Angular Motion

• Flexion: Decreases the angle.

• Extension: Increases the angle (reverse of flexion).

• Hyperextension: Extending beyond anatomical position.

• Abduction: Moving away from midline.

• Adduction: Moving towards midline.

• Circumduction: Circular movement of a limb.

3. Rotational Motion

• Turning around a longitudinal axis (e.g., atlantoaxial joint).

4. Special Movements

• Supination: Palms facing anteriorly.

• Pronation: Palms facing posteriorly.

• Dorsiflexion: Lifting foot toward shin.

• Plantar Flexion: Pointing toes.

• Inversion: Turning sole medially.

• Eversion: Turning sole laterally.

• Protraction: Moving body part forward.

• Retraction: Moving body part backward.

• Elevation: Moving body part superiorly.

• Depression: Moving body part inferiorly.

Summary of Joint Classes

• Fibrous Joints: Collagen fibers uniting adjoining bones.

• Cartilaginous Joints: Bones united by cartilage.

• Synovial Joints: Adjoining bones covered in articular cartilage, separated by a joint cavity, enclosed within an articular capsule.

• Mobility: Ranges from immobile to freely mobile, depending on the design.