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).