Articulations and Movement

Objectives

• Define and describe the three functional categories of joints.

• Define and describe the three structural categories of joints and their subcategories.

• Identify bones that articulate with each other and the specific kind of joint.

• Identify the types of synovial joints.

• Demonstrate or identify various body movements.

• Describe the structures of a generic synovial joint.

• Identify and classify joint categories using real bones/skeletons.

Classification of Joints

Functional Classification of Joints

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

• Synarthrosis: Immovable joints. Example: Sutures in the skull.

• Amphiarthrosis: Slightly movable joints. Example: Inferior tibiofibular joint.

• Diarthrosis: Freely movable joints. Example: Most synovial joints such as the shoulder and knee.

Structural Classification of Joints

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

• Fibrous Joints: Bones are joined by dense fibrous connective tissue; no joint cavity. Subtypes include sutures, syndesmoses, and gomphoses.

• Cartilaginous Joints: Bones are united by cartilage; no joint cavity. Subtypes include synchondroses and symphyses.

• Synovial Joints: Bones are separated by a fluid-filled joint cavity; allow free movement. Subtypes include plane, hinge, pivot, condyloid, saddle, and ball-and-socket joints.

Examples of Joint Types and Subtypes

• Suture (Fibrous): Cranial bones; immovable (synarthrosis).

• Inferior Tibiofibular Joint (Fibrous - Syndesmosis): Tibia and fibula; slightly movable (amphiarthrosis).

• Sternocostal Joint (Cartilaginous - Synchondrosis): Sternum and rib 1; immovable (synarthrosis).

• Intermediate Radioulnar Joint (Fibrous - Syndesmosis): Radius and ulna; slightly movable (amphiarthrosis).

Synovial Joint Subtypes

Synovial joints are the most movable type of joint and are classified by the shapes of their articulating surfaces and the movements they allow:

• Plane Joint: Allows gliding movements (e.g., intercarpal joints).

• Hinge Joint: Allows flexion and extension (e.g., elbow, knee).

• Pivot Joint: Allows rotation (e.g., proximal radioulnar joint).

• Condyloid Joint: Allows flexion, extension, abduction, adduction (e.g., wrist).

• Saddle Joint: Allows similar movements to condyloid but with greater range (e.g., thumb carpometacarpal joint).

• Ball-and-Socket Joint: Allows movement in all axes and planes (e.g., shoulder, hip).

Articular Motions

Types of Movements at Joints

Joints allow various types of movements, which are essential for body mobility and function:

• Flexion: Decreases the angle between two bones (e.g., bending the elbow).

• Extension: Increases the angle between two bones (e.g., straightening the knee).

• Abduction: Movement away from the midline (e.g., raising the arm sideways).

• Adduction: Movement toward the midline (e.g., lowering the arm to the side).

• Rotation: Movement around a longitudinal axis (e.g., turning the head).

• Circumduction: Circular movement combining flexion, extension, abduction, and adduction (e.g., arm circles).

• Supination: Rotating the forearm so the palm faces up.

• Pronation: Rotating the forearm so the palm faces down.

• Dorsiflexion: Lifting the foot upwards toward the shin.

• Plantar Flexion: Pointing the toes downward.

Joints on Skeletal Model

Representative Joint Table

The following table summarizes key joints, their articulating bones, functional and structural types, subtypes, and associated movements:

Structure of a Generic Synovial Joint

Synovial joints have a unique structure that allows for free movement:

• Articular Cartilage: Covers the ends of bones, reducing friction and absorbing shock.

• Joint (Synovial) Cavity: Space filled with synovial fluid.

• Synovial Fluid: Lubricates the joint and nourishes articular cartilage.

• Articular Capsule: Encloses the joint cavity; consists of an outer fibrous layer and an inner synovial membrane.

• Ligaments: Strengthen and support the joint.

• Bursae: Fluid-filled sacs that reduce friction between joint structures.

Key Equations and Concepts

• Range of Motion (ROM): The degree of movement that occurs at a joint. Influenced by joint structure, ligaments, and muscle tone.

• Classification Formula:

Comparison of Joint Types

Joints can be compared based on their mobility and structure:

Additional info:

• Joint classification is essential for understanding movement and diagnosing joint disorders.

• Synovial joints are the most common and versatile in the human body.