Joint Classification and Structure: Study Guide for Anatomy & Physiology

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Joints (Articulations) in the Human Body

Introduction

Joints, also known as articulations, are the connections between bones in the skeletal system. They play a crucial role in providing mobility and stability to the skeleton, allowing for a wide range of movements and supporting the body’s structure.

What is an Articulation?

Definition: An articulation is a point where two or more bones meet. These points are commonly referred to as joints.
Function: Articulations allow for movement and provide mechanical support.

Functions of Joints

Enable movement of the body and its parts
Hold the skeleton together
Provide stability and flexibility
Absorb shock during movement

Classification of Joints

Functional Joint Classifications

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

Synarthroses: Immovable joints. Example: Sutures of the skull.
Amphiarthroses: Slightly movable joints. Example: Intervertebral discs between vertebrae.
Diarthroses: Freely movable joints. Example: Shoulder, knee, and hip joints.

Structural Joint Classifications

Joints are also classified structurally based on the material binding the bones and whether a joint cavity is present:

Fibrous Joints: Bones are joined by dense connective tissue; no joint cavity. Example: Sutures in the skull.
Cartilaginous Joints: Bones are joined by cartilage; no joint cavity. Example: Pubic symphysis, intervertebral discs.
Synovial Joints: Bones are separated by a fluid-filled joint cavity; allows free movement. Example: Elbow, knee, shoulder.

Types of Fibrous Joints

Sutures: Found only in the skull; bones are tightly bound by minimal fibrous tissue.
Syndesmoses: Bones are connected by a ligament; allows more movement than a suture. Example: Distal tibiofibular joint.
Gomphoses: Peg-in-socket fibrous joint. Example: Teeth in their sockets.

Types of Cartilaginous Joints

Synchondroses: Bones united by hyaline cartilage. Example: Epiphyseal plates in growing children.
Symphyses: Bones united by fibrocartilage. Example: Pubic symphysis, intervertebral discs.

Distinguishing Features of Synovial Joints

Articular cartilage: Covers the ends of bones to reduce friction.
Joint (articular) cavity: Space that contains synovial fluid.
Articular capsule: Double-layered capsule enclosing the joint cavity.
Synovial fluid: Lubricates and nourishes the articular cartilage.
Reinforcing ligaments: Strengthen and support the joint.
Nerves and blood vessels: Supply the joint with nutrients and sensory information.
Additional info: Some synovial joints also contain menisci (articular discs) or bursae to further reduce friction and improve fit.

Types of Synovial Joints and Examples

Type	Movement	Example
Plane (Gliding)	Sliding or translational	Intercarpal joints (wrist)
Hinge	Flexion and extension	Elbow, knee
Pivot	Rotation	Atlantoaxial joint (neck)
Condyloid (Ellipsoid)	Flexion, extension, abduction, adduction, circumduction	Metacarpophalangeal joints (knuckles)
Saddle	Similar to condyloid, but with greater movement	Carpometacarpal joint of the thumb
Ball-and-Socket	Flexion, extension, abduction, adduction, rotation, circumduction	Shoulder, hip

Summary Table: Joint Classifications

Classification	Types	Movement	Examples
Functional	Synarthroses, Amphiarthroses, Diarthroses	Immovable, Slightly movable, Freely movable	Sutures, Intervertebral discs, Shoulder
Structural	Fibrous, Cartilaginous, Synovial	Varies by type	Skull sutures, Pubic symphysis, Knee

Key Terms

Articulation: Joint; point of contact between bones.
Synarthrosis: Immovable joint.
Amphiarthrosis: Slightly movable joint.
Diarthrosis: Freely movable joint.
Synovial fluid: Lubricating fluid in synovial joints.