NT

Joints: Structural and Functional Classifications

Classification of Joints

  • Joints are sites where bones meet, providing mobility and holding the skeleton together.

  • Classifications:

    • Structural: Fibrous, Cartilaginous, Synovial (based on binding material).

    • Functional: Synarthroses (immovable), Amphiarthroses (slightly movable), Diarthroses (freely movable).

Fibrous Joints

  • Bones joined by dense fibrous connective tissue; no joint cavity.

  • Types:

    • Sutures: Skull joints that ossify in middle age.

    • Syndesmoses: Bones connected by ligaments (e.g., tibiofibular joint, interosseous membrane).

    • Gomphoses: Peg-in-socket joints (teeth in sockets).

Cartilaginous Joints

  • Bones united by cartilage; no joint cavity, not highly movable.

  • Types:

    • Synchondroses: Hyaline cartilage unites bones (e.g., epiphyseal plate).

    • Symphyses: Fibrocartilage unites bones (e.g., intervertebral joints).

Synovial Joints

  • Bones separated by a fluid-filled joint cavity; all are diarthrotic.

  • Features:

    • Articular cartilage: Hyaline cartilage prevents crushing.

    • Joint cavity: Fluid-filled space.

    • Articular capsule: Fibrous layer and synovial membrane.

    • Synovial fluid: Lubricates and nourishes.

    • Ligaments: Reinforce the joint.

    • Nerves and vessels: Detect pain and supply filtrate.

  • Other features: Fatty pads and articular discs (menisci).

Bursae and Tendon Sheaths

  • Synovial fluid bags that reduce friction.

  • Bursae: Between ligaments, muscles, skin, tendons, or bones.

  • Tendon sheaths: Wrap around tendons.

Stability of Synovial Joints

  • Influenced by articular surface shape, ligament number, and muscle tone.

Movements Allowed

  • Nonaxial, Uniaxial, Biaxial, Multiaxial.

  • Types:

    • Gliding: Flat surfaces slip.

    • Angular: Flexion, Extension, Abduction, Adduction, Circumduction.

    • Rotation: Medial or lateral.

Special Movements

  • Supination/Pronation, Dorsiflexion/Plantar flexion, Inversion/Eversion, Protraction/Retraction, Elevation/Depression, Opposition.

Types of Synovial Joints

  • Plane, Hinge, Pivot, Condylar, Saddle, Ball-and-socket.

Selected Synovial Joints

  • Jaw (TMJ), Shoulder, Elbow, Hip, Knee.

Temporomandibular Joint (TMJ)

  • Hinge joint for depression/elevation and gliding for lateral excursion.

  • Prone to dislocation; symptoms include pain and stiffness.

Shoulder (Glenohumeral) Joint

  • Freely moving; stability sacrificed.

  • Reinforced by rotator cuff tendons.

  • Common anterior/inferior dislocations.

Elbow Joint

  • Hinge joint for flexion/extension.

  • Ulnar and radial collateral ligaments.

Hip (Coxal) Joint

  • Ball-and-socket; deep socket limits motion but enhances stability.

Knee Joint

  • Complex joint with femoropatellar and tibiofemoral components.

  • Stabilized by cruciate and collateral ligaments.

  • Vulnerable to injuries (3 C’s).

Disorders of Joints

Common Joint Injuries

  • Cartilage tears: Repaired with arthroscopic surgery.

  • Sprains: Ligament tears; treated with repair or grafts.

  • Dislocations: Bones out of alignment; must be reduced.

Inflammatory/Degenerative Conditions

  • Bursitis: Bursa inflammation.

  • Tendonitis: Tendon sheath inflammation.

  • Arthritis: >100 types; Osteoarthritis, Rheumatoid arthritis, Gouty arthritis, Lyme disease.

Developmental Aspects

  • Synovial joints resemble adult joints by week 8 of development.

  • Use modifies joint size and flexibility.

  • Aging affects joints; exercise postpones problems.