9 - Joints A Final

Joints Overview

  • Definition of joints: Points of contact between bones, cartilage, or teeth.

  • Study of joints: Arthrology.

Classification of Joints

Learning Objectives

  1. Define a joint.

  2. Compare structural and functional classifications of joints.

  3. Explain the inverse relationship between mobility and stability.

Structural Classification

  • Fibrous joints: Dense connective tissue holds bones together; immobile.

  • Cartilaginous joints: Bones joined by cartilage; immobile or slightly mobile.

  • Synovial joints: Ligaments connect bones with fluid-filled joint cavity; freely mobile.

Functional Classification

  • Synarthroses: Immobile joints (fibrous or cartilaginous).

  • Amphiarthroses: Slightly mobile joints (fibrous or cartilaginous).

  • Diarthroses: Freely mobile joints (all synovial).

Mobility vs Stability in Joints

  • Range of motion: Varies from immobile to extensive movement.

  • Inverse relationship: More stability means less mobility.

  • Example: Skull sutures are stable but immobile.

Types of Joints

Fibrous Joints

  1. Gomphoses: "Peg in a socket" like teeth in mandible/maxilla; immobile (synarthroses).

  2. Sutures: Found between skull bones; allow growth in childhood; become ossified with age.

  3. Syndesmoses: Bones bound by membrane; slightly mobile (amphiarthroses).

Cartilaginous Joints

  • Types:

    • Synchondroses: Joined by hyaline cartilage; immobile.

    • Symphyses: Pads of fibrocartilage; slightly mobile.

Synovial Joints

  • Key features:

    • Joint cavity with synovial fluid.

    • Articular capsule, cartilage, ligaments.

  • Types of synovial joints:

    • Uniaxial, biaxial, multiaxial.

    • Specific shapes (plane, hinge, pivot, condylar, saddle, ball-and-socket).

Joint Movements

Types of Movements

  1. Gliding: Opposing surfaces slide; e.g., carpals.

  2. Angular Motion: Changes angle between bones; includes flexion, extension, hyperextension, lateral flexion, abduction, adduction, circumduction.

  3. Rotational Motion: Bone rotates on its axis; medial and lateral rotation.

  4. Special Movements: Depression, elevation, dorsiflexion, plantar flexion, eversion, inversion, protraction, retraction, opposition.

Synovial Joints and Levers

Lever Mechanics

  • Definition: Rigid object rotating around a fulcrum.

  • Types of levers:

    1. First-Class: Fulcrum between effort and resistance (e.g., scissors).

    2. Second-Class: Resistance between fulcrum and effort (e.g., standing on tiptoe).

    3. Third-Class: Effort between resistance and fulcrum (e.g., elbow joint).