Nurs 1002-Obj #8

Joints (Articulations)

Introduction to Joints

Joints, also known as articulations, are sites where two or more bones meet. They provide the skeleton with mobility and hold the skeleton together, playing a crucial role in movement and stability.

• Definition: A joint is the location at which bones connect, allowing for movement and providing structural support.

• Function: Joints enable movement and protect internal organs by absorbing shock.

Primary Joint Classifications

Structural Classifications

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

• Fibrous Joints: Bones joined by dense fibrous connective tissue; no joint cavity; mostly immovable.

• Cartilaginous Joints: Bones united by cartilage; no joint cavity; slightly movable.

• Synovial Joints: Bones separated by a fluid-filled joint cavity; freely movable.

Functional Classifications

Joints are also classified functionally by the amount of movement they allow:

• Synarthroses: Immovable joints

• Amphiarthroses: Slightly movable joints

• Diarthroses: Freely movable joints

Types of Fibrous Joints

Fibrous Joint Subtypes

Fibrous joints are connected by dense fibrous connective tissue and are generally immovable.

• Sutures: Rigid, interlocking joints found in the skull. They allow for growth during youth and eventually ossify to become immovable.

• Syndesmoses: Bones connected by ligaments. Example: Inferior tibiofibular joint, interosseous membrane between radius and ulna.

• Gomphoses: Peg-in-socket joints. Example: Tooth held in its socket by the periodontal ligament.

Types of Cartilaginous Joints

Cartilaginous Joint Subtypes

Cartilaginous joints unite bones using cartilage and lack a joint cavity.

• Synchondroses: Bar or plate of hyaline cartilage unites bones. Example: Epiphyseal plate in children, cartilage of the first rib with the manubrium of the sternum.

• Symphyses: Bones united by fibrocartilage. Example: Intervertebral joints, pubic symphysis.

Synovial Joints

Structural Characteristics of Synovial Joints

Synovial joints are the most movable type of joint and are characterized by a fluid-filled joint cavity.

• Articular Cartilage: Hyaline cartilage covers the ends of bones, reducing friction and absorbing shock.

• Joint (Synovial) Cavity: Small, fluid-filled space unique to synovial joints.

• Articular Capsule: Two layers thick; encloses the joint cavity.

• Synovial Membrane: Loose connective tissue that produces synovial fluid, which lubricates and nourishes the articular cartilage.

• Synovial Fluid: Slippery filtrate of plasma and hyaluronic acid; reduces friction and removes debris.

• Reinforcing Ligaments: Strengthen and stabilize the joint.

• Nerves and Blood Vessels: Detect pain, monitor joint position, and supply nutrients for synovial fluid.

Bursae and Tendon Sheaths

Bursae and tendon sheaths are accessory structures associated with synovial joints that reduce friction.

• Bursae: Flattened sacs containing synovial fluid; act as cushions where ligaments, tendons, or bones rub together.

• Tendon Sheaths: Elongated bursae wrapped around tendons subjected to friction.

Factors Determining Stability of Synovial Joints

Joint stability is essential to prevent dislocations and is determined by several factors:

• Articular Surface: The shape of the bone surfaces; shallow surfaces are less stable than ball-and-socket joints.

• Ligament Number and Location: More ligaments generally mean a stronger joint.

• Muscle Tone: Keeps tendons taut as they cross joints; most important factor in joint stability.

Types of Synovial Joint Movements

Movement Types

Synovial joints allow several types of movements, classified by the axes and planes in which they occur:

• Gliding: One flat bone surface glides or slips over another.

• Angular Movements: Change the angle between bones (e.g., flexion, extension, abduction, adduction).

• Rotation: Bone turns around its own long axis (e.g., rotation of the head, humerus, or femur).

• Special Movements: Include pronation, supination, dorsiflexion, plantar flexion, inversion, eversion, protraction, retraction, elevation, and depression.

Major Types of Synovial Joints

Classification by Shape and Movement

Synovial joints are classified into six types based on the shape of their articular surfaces and the movements they allow:

Type	Movement	Example
Plane	Nonaxial (gliding)	Intercarpal joints, joints between vertebral articular surfaces
Hinge	Uniaxial (flexion/extension)	Elbow, knee, interphalangeal joints
Pivot	Uniaxial (rotation)	Proximal radioulnar joint, atlantoaxial joint
Condylar (Ellipsoid)	Biaxial (flexion/extension, abduction/adduction)	Metacarpophalangeal (knuckle) joints, wrist joints
Saddle	Biaxial (flexion/extension, abduction/adduction)	Carpometacarpal joint of the thumb
Ball-and-Socket	Multiaxial (all movements)	Shoulder, hip joints

Clinical Implications

Joint Injuries and Disorders

Joints are susceptible to injuries and disorders due to their mobility and structural complexity.

• Sprains: Ligaments are stretched or torn; common in ankle, knee, and lumbar region.

• Dislocations (Luxations): Bones are forced out of alignment; often accompanied by sprains and inflammation.

• Bursitis and Tendonitis: Inflammation of bursae or tendon sheaths due to overuse or trauma.

• Arthritis: Inflammatory or degenerative diseases that damage joints (e.g., osteoarthritis, rheumatoid arthritis, gouty arthritis).

Example: Shoulder dislocations are common due to the joint's mobility and weak anterior/inferior reinforcement, especially when the humerus is rotated laterally and force is applied.

Additional info: The notes above expand on the brief points in the slides, providing definitions, examples, and clinical context for each joint type and movement.