Articulations: Functional and Structural Classifications

Functional Classifications of Articulations

Articulations, or joints, are classified functionally based on the degree of movement they allow. The three main functional classifications are:

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

• Amphiarthrosis: Slightly movable joints. Example: Intervertebral discs between vertebrae.

• Diarthrosis: Freely movable joints. Example: Shoulder (glenohumeral) joint.

Additional info: These functional categories correspond to structural types: fibrous (synarthrosis), cartilaginous (amphiarthrosis), and synovial (diarthrosis).

Structural Categories of Joints

• Fibrous Joints: Bones joined by dense connective tissue; no joint cavity. Example: Sutures in the skull.

• Cartilaginous Joints: Bones joined by cartilage; no joint cavity. Example: Pubic symphysis.

• Synovial Joints: Bones separated by a fluid-filled joint cavity; most movable type. Example: Knee joint.

Degenerative Diseases of Joints

Arthro and Arthritis

• Arthro-: Refers to a joint.

• Arthritis: Refers to the degenerative disease of a joint, characterized by inflammation and degeneration.

Osteoarthritis

• Definition: A degenerative joint disease involving inflammation and breakdown of joint cartilage and underlying bone.

• Effects: Affects bone ends in joints, leading to pain and reduced mobility.

• Common Sites: Knees, hips, hands, and spine.

Synovial Joints: Structure and Function

Main Components of a Synovial Joint

• Articular Cartilage: Covers bone ends, reduces friction.

• Joint (Synovial) Cavity: Space containing synovial fluid.

• Articular Capsule: Encloses joint cavity; consists of fibrous and synovial layers.

• Synovial Fluid: Lubricates and nourishes joint.

• Ligaments: Strengthen and support joint.

• Nerves and Blood Vessels: Supply joint tissues.

Accessory Structures

• Bursae: Fluid-filled sacs that reduce friction.

• Tendons: Connect muscle to bone, stabilize joint.

• Menisci: Pads of fibrocartilage that improve fit and absorb shock.

Functions of Synovial Fluid

• Lubricates articular surfaces.

• Reduces friction during movement.

• Nourishes articular cartilage.

• Acts as a shock absorber.

Types of Synovial Joints

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

Joint Movements and Terminology

Terms Used for Anatomical Movements

• Flexion: Decreases the angle between bones.

• Extension: Increases the angle between bones.

• Abduction: Movement away from the midline.

• Adduction: Movement toward the midline.

• Rotation: Movement around an axis.

• Circumduction: Circular movement combining flexion, extension, abduction, and adduction.

Movements Provided by Major Joints

• Shoulder (Ball-and-Socket): Flexion, extension, abduction, adduction, rotation, circumduction.

• Elbow (Hinge): Flexion, extension.

• Hip (Ball-and-Socket): Flexion, extension, abduction, adduction, rotation, circumduction.

• Knee (Hinge): Flexion, extension (limited rotation when flexed).

• Ankle (Hinge): Dorsiflexion, plantarflexion.

• Wrist (Condyloid): Flexion, extension, abduction, adduction.

Factors Affecting Joint Stability and Range of Motion

• Shape of articular surfaces

• Number and position of ligaments

• Muscle tone and tendons crossing the joint

• Presence of accessory structures (menisci, labra)

Axial and Appendicular Skeleton: Common Joints

• Axial Skeleton Joints: Skull sutures, intervertebral joints, sternocostal joints.

• Appendicular Skeleton Joints: Shoulder, elbow, wrist, hip, knee, ankle joints.

Arthritis: Components and Types

• Components: Inflammation of joint tissues, degeneration of cartilage, pain, swelling, reduced mobility.

• Types: Osteoarthritis, rheumatoid arthritis, gouty arthritis.

Sprain vs. Strain

• Sprain: Injury to ligaments caused by overstretching or tearing.

• Strain: Injury to muscles or tendons due to overstretching or tearing.

• Key Difference: Sprains affect ligaments; strains affect muscles/tendons.