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

Joints (Articulations)

Overview of Joints

Joints, also known as articulations, are anatomical structures where two or more bones meet. They are essential for movement, stability, and growth within the skeletal system.

• Functions of Joints:

  • Movement: Allow bones to move relative to each other.

  • Stability: Hold the skeleton together and maintain posture.

  • Growth: Permit bone growth during development.

• Classification of Joints:

  • By Function (degree of movement permitted)

  • By Structure (type of connective tissue and presence/absence of a joint cavity)

Functional Classification of Joints

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

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

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

Structural Classification of Joints

Fibrous Joints

Fibrous joints are connected by dense connective tissue, mainly collagen. They lack a joint cavity and permit little to no movement.

• Types/Examples:

  • Sutures: Found between bones of the skull; immovable.

  • Syndesmoses: Bones connected by a ligament (e.g., distal tibiofibular joint); slightly movable.

  • Gomphoses: Peg-in-socket joints (e.g., teeth in alveolar sockets); immovable.

Illustration: Sutures (skull), syndesmosis (radius and ulna), gomphosis (tooth in socket).

Cartilaginous Joints

Cartilaginous joints are united by cartilage and lack a joint cavity. They allow more movement than fibrous joints but less than synovial joints.

• Types/Examples:

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

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

Summary Table: Joint Types and Examples

Structural Type	Functional Type	Examples	Movement
Fibrous: Suture	Synarthrosis	Skull sutures	Immovable
Fibrous: Syndesmosis	Amphiarthrosis	Distal tibiofibular joint	Slightly movable
Fibrous: Gomphosis	Synarthrosis	Tooth in socket	Immovable
Cartilaginous: Synchondrosis	Synarthrosis	Epiphyseal plate, first sternocostal joint	Immovable
Cartilaginous: Symphysis	Amphiarthrosis	Pubic symphysis, intervertebral discs	Slightly movable

Additional info: Synovial joints, their structure, and movement types are typically covered in the next section of this chapter.