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

Joints (Articulations)

Definition and Functions

Joints, also known as articulations, are sites where two or more bones meet. They are essential for both the mobility and stability of the skeletal system.

• Definition: An articulation is the site where two or more bones meet.

• Functions of joints:

  • Give the skeleton mobility

  • Hold the skeleton together

Classification of Joints

Functional Classification

Joints are classified functionally based on the amount of movement they allow.

• Synarthroses: Immovable joints

• Amphiarthroses: Slightly movable joints

• Diarthroses: Freely movable joints (all synovial joints; most abundant type in the body)

Structural Classification

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

• Fibrous joints: Bones joined by fibrous tissue; no joint cavity

• Cartilaginous joints: Bones united by cartilage; no joint cavity

• Synovial joints: Bones separated by a fluid-filled joint cavity; only type with a joint cavity

Fibrous Joints

General Features

Fibrous joints are connected by dense connective tissue and are mostly immovable.

• No joint cavity

• Types:

  • Sutures (seams)

  • Syndesmoses (sin"des-mo’sēz)

  • Gomphoses (gom-fo’sēz)

Types of Fibrous Joints

• Sutures:

  • Occur between bones of the skull

  • Comprised of interlocking junctions filled with connective tissue fibers

  • Bind bones tightly together but allow for growth during youth

• Syndesmoses:

  • Bones connected by a fibrous tissue ligament

  • Immovable to slightly movable

  • Example: Connection between tibia and fibula, and the radius and ulna

• Gomphoses:

  • Peg-in-socket fibrous joint between a tooth and its socket

Suture, Syndesmosis & Gomphosis (Comparison Table)

Type	Location	Movement	Example
Suture	Skull	Immovable	Coronal suture
Syndesmosis	Between long bones	Slightly movable	Distal tibiofibular joint
Gomphosis	Teeth sockets	Immovable	Tooth in alveolar socket

Cartilaginous Joints

General Features

Cartilaginous joints unite bones with cartilage and lack a joint cavity. They allow little to no movement.

• Types:

  • Synchondroses (sin"kon-dro’sis)

  • Symphyses (sim’fih-sēz)

Types of Cartilaginous Joints

• Synchondroses:

  • Bar or plate of hyaline cartilage unites the bones

  • All are synarthrotic (immovable)

  • Examples: Epiphyseal plates of children, costal cartilage of first rib and sternum

• Symphyses:

  • Hyaline cartilage covers the articulating surfaces of the bone and is fused to an intervening pad of fibrocartilage

  • All are amphiarthrotic (slightly movable)

  • Examples: Intervertebral joints, pubic symphysis

Comparison of Synchondroses and Symphyses

Type	Cartilage Type	Movement	Example
Synchondrosis	Hyaline cartilage	Immovable (synarthrotic)	Epiphyseal plate, first sternocostal joint
Symphysis	Fibrocartilage (with hyaline covering)	Slightly movable (amphiarthrotic)	Pubic symphysis, intervertebral discs

Additional info: The notes continue with synovial joints, their structure, types, and clinical aspects, which would be included in a full study guide for this chapter.