Basic Functions of Joints

Basic Functions of Joints

• Joints, also known as articulations, are essential to the skeletal system.
• Their primary roles include enabling movement, providing stability, and allowing for growth.

Enable Movement

• Joints allow bones to move relative to each other.
• This movement is facilitated by surrounding muscles contracting.
• Examples include walking, running, bending, and lifting.

Provide Stability

• Some joints are designed for maximum stability, limiting movement.
• This is crucial for protecting vital structures like the brain and spine.

Allow for Growth

• Joints like epiphyseal plates in long bones are vital during development.
• These temporary joints facilitate lengthening of long bones during childhood and adolescence.

Classification of Joints

• Joints are classified functionally based on the amount of movement they allow.
• They are also structurally classified based on their anatomical features.

Functional Classification

• This classification of joints focuses on the amount of mobility they offer.

Synarthrosis

• Definition: Joints with no movement between articulating bones.
• Stability: Provides maximum stability.
• Examples: Sutures in the skull and the gomphosis joint (teeth).

Amphiarthrosis

• Definition: Joints that allow a small amount of movement between bones.
• Stability: Offers significant stability while permitting limited movement.
• Examples: Intervertebral discs and the pubic symphysis.

Diarthrosis

• Definition: Freely movable joints.
• Stability: Offers the least amount of stability.
• Examples: Most joints in the limbs, including the knee, elbow, and shoulder.

Structural Classification

• This classification system focuses on the connective tissue connecting bones and the presence (or absence) of a joint space.

Fibrous Joints

• Definition: Joints united by collagen fibers of dense regular connective tissue.
• Joint Space: No joint space is present.
• Functional Classification: Typically synarthroses or amphiarthroses.
• Examples: Sutures in the skull, syndesmoses (radius and ulna), and gomphoses (teeth).

Cartilaginous Joints

• Definition: Joints with cartilage between articulating bones (hyaline or fibrocartilage).
• Joint Space: No joint space is present.

Synovial Joints

• Definition: Joints with a fluid-filled joint cavity containing synovial fluid.
• Joint Space: A fluid-filled joint space is present.
• Functional Classification: Classified as diarthroses.
• Examples: Knee, elbow, hip, and shoulder joints.

Comparison of Fibrous Joints

• Fibrous joints are characterized by dense regular collagenous connective tissue that connects bones.
• Sutures: Joints in the skull, with interlocking edges connected by short collagen fibers.
• Gomphoses: Joints connecting teeth to their sockets.
• Syndesmoses: Joints connected by a ligament.

Comparison of Cartilaginous Joints

• Cartilaginous joints connect bones using cartilage and lack a joint cavity.
• Synchondroses: Joints with hyaline cartilage (e.g., epiphyseal plates in growing bones).
• Symphyses: Joints with fibrocartilage (e.g., pubic symphysis and intervertebral discs).

Structural Components of a Synovial Joint

• Joint Cavity (Synovial Cavity): Space between articulating bones.
• Articular Capsule: Outer fibrous layer and inner synovial membrane.
• Synovial Fluid: Lubricates and nourishes the joint.
• Articular Cartilage: Covers articulating surfaces for smooth movement.
• Other Components: Adipose tissue, nerves, and blood vessels.

Comparing Synovial Joints with Fibrous and Cartilaginous

• Synovial Joints: Freely movable (diarthroses).
• Fibrous Joints: Generally immovable (synarthroses).
• Cartilaginous Joints: Permit limited movement (amphiarthroses).

Movements of Synovial Joints (Functional Classes)

• Nonaxial: Motion in one or more planes, not rotation around an axis.
• Uniaxial: Movement around a single axis.
• Biaxial: Movement around two axes.
• Multiaxial (Triaxial): Movement around three axes.

Types of Movements

• Gliding: Sliding motion between surfaces.
• Angular: Changes the angle between bones (flexion, extension, abduction, adduction, etc.).
• Rotational: Bone pivoting around its longitudinal axis.
• Special Movements: Unique movements at specific joints (opposition, reposition, depression, elevation).

Anatomical Features of Synovial Joints

• Plane joint: Flat or slightly curved surfaces.
• Hinge joint: Convex surface fits into a concave surface (flexion/extension only).
• Pivot joint: Rounded surface that fits into a groove (rotation).
• Condylar joint: Oval convex surface fits into a shallow concave surface (flexion, extension, abduction, adduction).
• Saddle joint: Each articulating bone has both a concave and convex surface (Biaxial, with much motion).
• Ball-and-Socket joint: Sphere-shaped end of one bone fits into a cup on another (Multiaxial, most motion).

Elbow and Knee Joint Structural Features

• Elbow: Hinge joint with two main articulations, providing mostly flexion/extension movement
• Knee: Hinge joint with complex structure, enabling both flexion/extension and some rotation, while also being more vulnerable to injury.

Shoulder and Hip Joint Structural Features

• Shoulder: Ball-and-socket joint allowing wide range of movement at the cost of stability
• Hip: Similar type of joint enabling wider movement than the elbow but less movement than the shoulder, with increased stability.