Articulations: Functional and Structural Classifications, Synovial Joints, and Common Injuries

Articulations (Joints) in Anatomy & Physiology

Functional Classifications of Articulations

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

• Synarthrosis: Immovable joints

• Amphiarthrosis: Slightly movable joints

• Diarthrosis: Freely movable joints

Example: The sutures of the skull are synarthroses, the pubic symphysis is an amphiarthrosis, and the shoulder joint is a diarthrosis.

Degenerative Diseases of Joints

Degenerative joint diseases refer to conditions that affect the structure and function of joints over time.

• Arthro: Refers to a joint.

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

• Osteoarthritis: A specific type of arthritis involving bone and joint inflammation/degeneration, typically affecting bone ends in joints.

Structural Classifications of Joints

Each functional category of joint is further classified structurally based on the material binding the bones and the presence or absence of a joint cavity.

Synarthrosis (Immovable Joints)

• Fibrous Joints

  • Sutures: Immovable joints found between the bones of the skull.

  • Gomphosis: Peg-in-socket joints, such as the binding of teeth to bony sockets.

• Cartilaginous Joints

  • Synchondrosis: Cartilaginous bridge between two articulating bones, e.g., connection between the ends of the first pair of vertebrosternal ribs and the sternum.

• Bony Fusion

  • Synostosis: Complete fusion of two bones, such as the frontal suture of the frontal bone and the epiphyseal lines of mature long bones.

Amphiarthrosis (Slightly Movable Joints)

• Fibrous Joints

  • Syndesmosis: Bones connected by a ligament, e.g., distal articulation between the tibia and fibula.

• Cartilaginous Joints

  • Symphysis: Bones separated by a wedge or pad of fibrous cartilage, e.g., the pubic symphysis.

Diarthrosis (Freely Movable Joints)

• Synovial Joints: Permit a wider range of motion than other types of joints. Typically located at the ends of long bones, such as those of the upper and lower limbs.

Synovial Joints

Main Components of a Synovial Joint

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

• Joint (Articular) Capsule: Encloses the joint cavity and is composed of an outer fibrous layer and an inner synovial membrane.

• Synovial Membrane: Produces synovial fluid.

• Synovial Fluid: Lubricates the joint, nourishes articular cartilage, and acts as a shock absorber.

• Accessory Structures: Includes ligaments, tendons, bursae, and menisci.

Functions of Synovial Fluid

• Lubrication of joint surfaces

• Nutrient distribution to articular cartilage

• Shock absorption during movement

Types of Synovial Joints

Synovial joints are classified based on the shapes of their articulating surfaces and the types of movement they allow.

Type	Description	Example
Gliding (Plane)	Flat surfaces slide past each other	Intercarpal joints
Hinge	Permit flexion and extension	Elbow, knee
Pivot	Rotation around a single axis	Atlantoaxial joint (between C1 and C2 vertebrae)
Condyloid (Ellipsoidal)	Oval articular surface fits into a depression	Wrist joint
Saddle	Articulating surfaces are concave and convex	Thumb (carpometacarpal joint)
Ball-and-Socket	Round head fits into a cup-shaped socket	Shoulder, hip

Movements Provided by Synovial Joints

• Shoulder: Flexion, extension, abduction, adduction, rotation, circumduction

• Elbow: Flexion, extension

• Hip: Flexion, extension, abduction, adduction, rotation, circumduction

• Knee: Flexion, extension, slight rotation

• Ankle: Dorsiflexion, plantarflexion, inversion, eversion

• Wrist: Flexion, extension, abduction, adduction

Factors Affecting Synovial Joint Stability and Range of Motion

• Shape of articulating surfaces

• Presence and strength of ligaments

• Muscle tone and tendons crossing the joint

• Amount of synovial fluid

Common Joints of the Axial and Appendicular Skeleton

• Axial Skeleton: Sutures (skull), intervertebral joints, temporomandibular joint

• Appendicular Skeleton: Shoulder, elbow, wrist, hip, knee, ankle

Arthritis and Joint Injuries

Components of Arthritis

• Inflammation of the joint

• Degeneration of articular cartilage

• Pain, swelling, and reduced mobility

Difference Between Sprain and Strain

• Sprain: Injury to ligaments caused by excessive stretching or tearing

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

Common Injuries of the Shoulder, Elbow, and Knee Joints

• Shoulder: Dislocation, rotator cuff tear

• Elbow: Tennis elbow (lateral epicondylitis), dislocation

• Knee: Ligament tears (ACL, MCL), meniscus injury, patellar dislocation

Additional info: Academic context and examples have been expanded for clarity and completeness.