Chapter 8: Joints (Articulations) – Structure, Function, and Disorders

Joints (Articulations)

Introduction to Joints

Joints, also known as articulations, are the sites where two or more bones meet. They play a crucial role in providing the skeleton with mobility while also holding the skeleton together for structural integrity.

• Definition: A joint (articulation) is a point of contact between bones, or between bone and cartilage.

• Functions:

  • Enable movement of the skeleton

  • Provide stability and support

Classification of Joints

Structural Classification

Joints are classified structurally based on the material binding the bones together and the presence or absence of a joint cavity.

• Fibrous Joints: Bones joined by dense fibrous connective tissue; no joint cavity.

• Cartilaginous Joints: Bones united by cartilage; no joint cavity.

• Synovial Joints: Bones separated by a fluid-filled joint cavity.

Functional Classification

Joints are also classified by the amount of movement they allow:

• Synarthroses: Immovable joints (e.g., sutures of the skull)

• Amphiarthroses: Slightly movable joints (e.g., intervertebral discs)

• Diarthroses: Freely movable joints (e.g., most limb joints)

Fibrous Joints

General Characteristics

Fibrous joints are connected by dense fibrous connective tissue and lack a joint cavity. Most are immovable, but the degree of movement depends on the length of the connective tissue fibers.

• Sutures: Synarthrotic (immovable); found between bones of the skull.

• Syndesmoses: Amphiarthrotic (slightly movable); bones connected by ligaments (e.g., distal tibiofibular joint).

• Gomphoses: Synarthrotic; peg-in-socket joints (e.g., teeth in alveolar sockets, connected by the periodontal ligament).

Table: Types of Fibrous Joints

Type	Movement	Example
Suture	Immovable (synarthrotic)	Skull sutures
Syndesmosis	Slightly movable (amphiarthrotic)	Distal tibiofibular joint
Gomphosis	Immovable (synarthrotic)	Tooth in alveolar socket

Cartilaginous Joints

General Characteristics

Cartilaginous joints are united by cartilage and, like fibrous joints, lack a joint cavity. They are not highly movable.

• Synchondroses: Synarthrotic (immovable); bones united by hyaline cartilage (e.g., epiphyseal plates in children, joint between first rib and sternum).

• Symphyses: Amphiarthrotic (slightly movable); bones united by fibrocartilage (e.g., intervertebral discs, pubic symphysis).

Table: Types of Cartilaginous Joints

Type	Movement	Example
Synchondrosis	Immovable (synarthrotic)	Epiphyseal plate, first sternocostal joint
Symphysis	Slightly movable (amphiarthrotic)	Pubic symphysis, intervertebral discs

Key Terms and Concepts

• Articulation: Another term for joint; the point where two bones meet.

• Synarthrosis: An immovable joint.

• Amphiarthrosis: A slightly movable joint.

• Diarthrosis: A freely movable joint.

• Ligament: A band of dense connective tissue that connects bones at a joint.

• Periodontal ligament: The fibrous connection in a gomphosis (tooth socket).

Examples and Applications

• Example of a Suture: The coronal suture between the frontal and parietal bones of the skull.

• Example of a Syndesmosis: The interosseous membrane between the radius and ulna in the forearm.

• Example of a Gomphosis: The joint between a tooth and its socket in the mandible or maxilla.

• Example of a Synchondrosis: The epiphyseal plate in a growing long bone.

• Example of a Symphysis: The pubic symphysis joining the two pubic bones.

Additional info: Later sections of this chapter (not shown in these slides) typically cover synovial joints, their structure, types, and joint disorders in detail.