Chapter 8: Joints – Structure, Classification, and Function

Joints (Articulations)

Definition and Function of Joints

Joints, also known as articulations, are the sites where two or more bones meet. They play a crucial role in the human body by providing both mobility and stability to the skeleton.

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

• Function: Joints allow for movement and flexibility of the skeleton, while also holding bones together and providing structural support.

Classification of Joints

Structural Classification

Joints are classified structurally based on the material binding the bones together and whether or not a joint cavity is present.

• 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 degree of movement they allow.

• Synarthroses: Immovable joints.

• Amphiarthroses: Slightly movable joints.

• Diarthroses: Freely movable joints.

Fibrous Joints

General Characteristics

Fibrous joints are connected by dense fibrous connective tissue and lack a joint cavity. Most are immovable.

• Types of Fibrous Joints:

  • Sutures

  • Syndesmoses

  • Gomphoses

Sutures

Sutures are rigid, interlocking joints found only in the skull. They are held together by very short connective tissue fibers, making them immovable (synarthrotic).

• Allow for growth during youth by containing short connective tissue fibers that permit expansion.

• In early adulthood (~22-25 years), sutures ossify and the skull bones fuse into a single unit, forming synostoses.

Syndesmoses

Syndesmoses are joints where bones are connected by ligaments. The amount of movement depends on the length of the connecting fibers.

• Short fibers: Little to no movement (e.g., inferior tibiofibular joint; synarthrotic).

• Longer fibers: More movement possible (e.g., interosseous membrane between radius and ulna; amphiarthrotic).

Gomphoses

Gomphoses are peg-in-socket joints, with the only examples being the teeth in their alveolar sockets of the jawbones.

• Immovable (synarthrotic).

• The fibrous connection is the periodontal ligament, which holds the tooth in place.

*Additional info: Further details on cartilaginous and synovial joints, as well as joint pathologies and injuries, are likely covered in subsequent slides or sections of the chapter.*