Joints and Articulations

Chapter 9: Joints

  • Definition of a Joint: A joint, also called an articulation or arthrosis, is a point of contact between two or more bones, cartilage and bone, or teeth and bone.

  • Classification of Joints:

    • Fibrous Joints: No synovial cavity; bones held together by dense irregular connective tissue; allow little to no movement.

Examples:

  • Syndesmosis: Bones are united by ligament or interosseous membrane (e.g., distal tibiofibular joint).

  • Suture: Found between skull bones; immovable.

  • Gomphosis: Joint between a tooth root and its bone socket, held by the periodontal ligament.

  • Cartilaginous Joints: No synovial cavity; bones connected by cartilage; allow slight movement.

  • Examples:

    • Synchondroses: Connected by hyaline cartilage (e.g., epiphyseal plate).

    • Symphyses: Connected by fibrocartilage (e.g., pubic symphysis).

  • Synovial Joints: Possess a synovial cavity; allow free movement.

  • Examples: Shoulder, knee, elbow.

  • Movements of Synovial Joints:

    • Gliding Movements: Flat bone surfaces move against one another.

    • Angular Movements: Change in angle between bones.

Types:

  • Flexion: Decrease in angle.

  • Extension: Increase in angle; return to anatomical position.

  • Lateral Flexion: Movement of the trunk.

  • Abduction: Movement away from midline.

  • Adduction: Movement toward midline.

  • Circumduction: Circular movement at a joint.

    Rotational Movements:

  • Lateral Rotation: Rotates away from midline.

  • Medial Rotation: Rotates toward midline.

    Special Movements:

  • Elevation: Lifting body parts vertically.

  • Depression: Lowering body parts vertically.

  • Protraction: Moving a body part forward.

  • Retraction: Moving a body part backward.

  • Inversion: Turning soles of feet inward.

  • Eversion: Turning soles of feet outward.

  • Dorsiflexion: Bending foot upwards.

  • Plantar Flexion: Bending foot downwards.

  • Supination: Rotating forearm palm up.

  • Pronation: Rotating forearm palm down.

  • Opposition: Moving thumb to touch fingertips.

  • Special Joints:

    • Plane Joint: Flat surfaces; allows gliding.

    • Hinge Joint: Cylindrical surfaces; allows flexion and extension.

    • Pivot Joint: Rounded surface fits into a ring; allows rotation.

    • Condyloid/Ellipsoid Joint: Oval projection fits into an oval depression; allows multiple movements.

    • Ball-and-Socket Joint: Spherical surface fits into a cup-like depression; allows the greatest range of movement.

    • Saddle Joint: Saddle-shaped surfaces; allows movement in multiple planes.

  • Injuries Affecting Joints:

    • Common issues include rotator cuff injuries for the shoulder, elbow dislocations, and ligament tears in the knee.

  • Aging Effects on Joints:

    • Decreased synovial fluid, thinning articular cartilage, and reduced ligament flexibility may occur with age.

  • Arthroplasty: Surgical procedure for joint replacement.

  • Other Joint Disorders: Conditions like arthritis, sprains, and tendonitis can affect joint health.