Skeletal System: Joints, Articulations, and Movements

SKELETAL SYSTEM - III JOINTS, ARTICULATIONS AND MOVEMENTS

INTRODUCTION

  • A joint, also known as an articulation, serves as a connection between adjacent bones or a bone and cartilage, enabling them to articulate (come together).

    • Classification of Joints:

    • Joints can be classified structurally and functionally.

      • Structural Classification:

      • Based on the connection strength of adjacent bones:

        • Fibrous connective tissue

        • Cartilage

        • Joint cavity filled with fluid (synovial)

      • Functional Classification:

      • Based on the degree of movement:

        • Immobile

        • Slightly mobile

        • Freely moveable

      • Movement relates to the functional requirements of the joint: strong, stable joints for protection, vs. flexible joints for mobility.

STRUCTURAL CLASSIFICATION OF JOINTS

  • Categories of Joints Based on Structure:

    • Fibrous Joint:

    • Definition: Adjacent bones united by fibrous connective tissue.

    • Cartilaginous Joint:

    • Definition: Bones joined by hyaline cartilage or fibrocartilage.

    • Synovial Joint:

    • Definition: Articulating surfaces of bones are not directly connected, but instead contact each other within a fluid-filled joint cavity.

    • Functionality: Allow for free movement, common in the body.

FUNCTIONAL CLASSIFICATION OF JOINTS

  • Categories of Joints Based on Functionality:

    • Synarthrosis: Immobile joints.

    • Amphiarthrosis: Slightly movable joints.

    • Diarthrosis: Freely movable joints (e.g., synovial joints).

    • Functional Classification of Structural Joints:

    • Fibrous Joints: Can be synarthrosis (e.g., sutures) or amphiarthrosis (e.g., syndesmosis).

    • Cartilaginous Joints: Can be synarthrosis (e.g., synchondrosis) or amphiarthrosis (e.g., symphysis).

    • Synovial Joints: All classified as diarthrosis.

SYNARTHROSIS JOINTS

  • Definition: Immobile or nearly immobile joints.

    • Importance: Provide strong union for protection of internal organs.

    • Examples:

    • Sutures: Fibrous joints between skull bones.

    • Manubriosternal Joint: Cartilaginous joint between the manubrium and body of the sternum.

AMPHIARTHROSIS JOINTS

  • Definition: Joints with limited mobility.

    • Examples:

    • Intervertebral Disc: Cartilaginous joint between adjacent vertebrae filled with fibrocartilage.

    • Pubic Symphysis: Cartilaginous joint anchoring pubic bones with limited mobility.

DIARTHROSIS JOINTS

  • Definition: Freely mobile joints, encompassing all synovial joints.

    • Common Locations: Primarily in the appendicular skeleton.

    • Classification by Axes of Motion:

    • Uniaxial: Rotation around one axis (Example: elbow joint).

    • Biaxial: Movements in two planes (Example: metacarpophalangeal joint).

    • Multiaxial: Movements in multiple planes (Example: shoulder and hip joints).

SUMMARY OF JOINT CLASSIFICATIONS

  • Structural Classifications and Associated Functional Types:

    • Fibrous:

    • Types: Synarthrosis / Amphiarthrosis.

    • Characteristics: Dense fibrous connective tissue, no joint cavity.

    • Examples: Skull sutures, syndesmosis.

    • Cartilaginous:

    • Types: Synarthrosis / Amphiarthrosis.

    • Characteristics: Cartilage, no joint cavity.

    • Examples: Intervertebral discs, pubic symphysis.

    • Synovial:

    • Type: Diarthrosis.

    • Characteristics: Articulating bones with articular cartilage, joint cavity, and articular capsule.

    • Examples: Shoulder, hip, elbow joints.

SYNOVIAL JOINT

  • Definition: Most common type of joint; characterized by a joint cavity.

    • Key Features:

    • Joint cavity filled with synovial fluid allows smooth movement.

    • Articulating surfaces not directly connected.

STRUCTURAL FEATURES OF SYNOVIAL JOINTS

  • Joint Cavity:

    • Definition: Space filled with synovial fluid allowing smooth bone movement.

    • Articular Capsule: Encloses the cavity; fibrous outer layer and synovial membrane.

    • Articular Cartilage: Covers bone ends to reduce friction & absorb shock. Acts like a Teflon® coating over bone surfaces.

    • Synovial Fluid: Provides lubrication and nourishment to articular cartilage; secreted by the synovial membrane.

    • Ligaments: Stabilize and strengthen joints (intrinsic or extrinsic), with dynamic support from muscles.

    • Tendons: Attach muscles to bones, providing additional support.

    • Articular Disc: Occurs in some joints, serving as a shock absorber (e.g., meniscus).

    • Bursae: Small sacs reducing friction between moving structures.

TYPES OF SYNOVIAL JOINTS

  • Classification by Structure & Function:

    • Types of Synovial Joints:

    • Pivot Joint:

      • Description: Rounded bone within a ring structure, allowing rotation (e.g., atlantoaxial joint).

      • Functional Class: Uniaxial.

    • Hinge Joint:

      • Description: Allows bending and straightening along one axis (e.g., elbow joint).

      • Functional Class: Uniaxial.

    • Condyloid Joint:

      • Description: Oval condyle in elliptical cavity allowing two planes of movement (e.g., knuckle joints).

      • Functional Class: Biaxial.

    • Saddle Joint:

      • Description: Saddle-shaped articulating surfaces allowing significant movement (e.g., thumb joint).

      • Functional Class: Biaxial.

    • Plane Joint:

      • Description: Flat surfaces allowing gliding movements (e.g., carpal bones).

      • Functional Class: Multiaxial.

    • Ball-and-Socket Joint:

      • Description: Rounded head fitting into a deep socket, allowing the greatest range of motion (e.g., shoulder joint).

      • Functional Class: Multiaxial.

MOVEMENTS OF SYNOVIAL JOINTS

  • General Movement Characteristics:

    • Movements produced by muscle contractions across joints.

    • Types of movements include flexion, extension, abduction, adduction, rotation, circumduction, and gliding.

  • Movement Types Description:

    • Flexion: Decreases the angle between two bones (bending).

    • Extension: Increases the angle between two bones (straightening).

    • Abduction: Moves a limb away from the midline.

    • Adduction: Moves a limb toward the midline.

    • Rotation: Movement around a bone's long axis.

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

    • Gliding: Sliding movements between flat surfaces, enabling subtle joint adjustments.

DETAILED MOVEMENTS

  • Flexion & Extension: Occur in the sagittal plane.

  • Abduction & Adduction: Occur in the coronal plane.

  • Circumduction: Common in ball-and-socket joints.

  • Rotation: Common in vertebrae, pivots (neck), ball-and-socket joints.

  • Supination & Pronation: Movements of the forearm.

  • Dorsiflexion & Plantar Flexion: Movements at the ankle joint.

  • Inversion & Eversion: Movements at the foot.

  • Protraction & Retraction: Movements of the scapula or mandible.

  • Elevation & Depression: Movements of the scapula and mandible.

  • Superior & Inferior Rotation: Movements of the scapula, important in abduction.

  • Opposition & Reposition: Specific thumb movements interacting with fingers.

SELECTED SYNOVIAL JOINTS

  • Shoulder Joint (Glenohumeral Joint):

    • Type: Ball-and-socket joint, largest range of motion.

    • Structural Details: Articulation between the humerus head and glenoid cavity; deepened by the glenoid labrum; supported by weak intrinsic ligaments and the rotator cuff.

    • Injuries: Common due to repetitive activities, leading to inflammation or tears.

  • Elbow Joint:

    • Type: Uniaxial hinge joint.

    • Components: Humeroulnar, humeroradial, proximal radioulnar joints.

    • Structure: Supported by strong intrinsic ligaments; allows flexion and extension; vulnerable to injuries like hyperextension.

  • Hip Joint:

    • Type: Multiaxial ball-and-socket joint.

    • Components: Stability due to acetabulum's depth and ligaments; holds body weight during movements.

  • Knee Joint:

    • Type: Largest joint, consisting of three articulations (femoropatellar, medial and lateral tibiofemoral).

    • Function: Primarily hinge motion; susceptible to injuries from hyperextension or twisting.

    • Functionality: Supports extension through the patellar ligament.

  • Temporomandibular Joint (TMJ):

    • Type: Modified hinge joint; allows diverse movements of the jaw; supported by an articular disc and ligaments.

JOINT DISORDERS

  • Common Disorders:

    • Osteoarthritis: Degeneration of cartilage, leading to pain and decreased motion.

    • Rheumatoid Arthritis: Autoimmune disorder causing joint inflammation.

    • Gout: Inflammatory arthritis from uric acid crystals.

    • Bursitis: Inflammation of bursa sacs.

    • Sprains and Strains: Ligament and muscle/tendon injuries, usually from overuse.