IS

Lecture 10_Joints

Chapter 8: Joints

Definition of Joints (Articulations)

  • Joints are the sites where two or more bones meet.

  • Functions of joints include:

    • Providing skeleton mobility.

    • Holding skeleton together.

  • Joints can be classified in two ways:

    • Functional Classification.

    • Structural Classification.

Functional Classification of Joints

  • Based on the amount of movement allowed by the joint, it is classified into three types:

    • Synarthroses: Immovable joints.

    • Amphiarthroses: Slightly movable joints.

    • Diarthroses: Freely movable joints.

Structural Classification of Joints

  • Based on the material binding bones together and the presence or absence of a joint cavity, it is classified into three types:

    • Fibrous Joints: No joint cavity, joined by dense fibrous connective tissue.

    • Cartilaginous Joints: Joined by cartilage without a joint cavity.

    • Synovial Joints: Bones are separated by a fluid-filled joint cavity.

Fibrous Joints

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

  • Generally immovable (synarthrotic), but may allow slight movement depending on the fiber length.

  • Types of fibrous joints include:

    • Sutures:

      • Rigid, interlocking joints in the skull.

      • Immovable.

      • Allow for growth during youth; may ossify into synostoses in middle age.

    • Syndesmoses:

      • Bones connected by longer ligaments (e.g., fibula and tibia).

      • Movement varies with fiber length.

    • Gomphoses:

      • Peg-in-socket joints (e.g., teeth in alveolar sockets).

      • Connected by the periodontal ligament.

Cartilaginous Joints

  • Bones united by cartilage and have no joint cavity.

  • Typically not highly movable.

  • Types include:

    • Synchondroses:

      • Bar/plate of hyaline cartilage uniting bones (e.g., epiphyseal plates).

      • Mostly immovable.

    • Symphyses:

      • Fibrocartilage unites bones with articular hyaline cartilage present.

      • Strong, flexible joints allowing slight movement (amphiarthroses).

Synovial Joints

  • Characterized by the presence of a fluid-filled joint cavity.

  • All synovial joints are diarthrotic (freely movable).

  • Features of synovial joints:

    1. Articular Cartilage: Hyaline cartilage preventing bone crushing.

    2. Joint (Synovial) Cavity: Small, fluid-filled space.

    3. Articular (Joint) Capsule:

      • Two layers:

        • External Fibrous layer (dense irregular connective tissue).

        • Inner Synovial membrane (loose connective tissue producing synovial fluid).

    4. Synovial Fluid:

      • Viscous, lubricating fluid containing hyaluronic acid and phagocytic cells.

    5. Reinforcing Ligaments: Three types:

      • Capsular: Thickened parts of fibrous layer.

      • Extracapsular: Outside the capsule.

      • Intracapsular: Deep to capsule, covered by synovial membrane.

    6. Nerves and Blood Vessels:

      • Nerve fibers detect pain and joint position; capillary beds supply fluid.

Other Features of Synovial Joints

  • Fatty Pads: Cushioning between fibrous layer and synovial membrane or bone.

  • Articular Discs (Menisci): Fibrocartilage structures improving fit, stability, and reducing wear.

  • Bursae: Synovial fluid-filled sacs reducing friction in joints where movement occurs.

  • Tendon Sheaths: Elongated bursae wrapped around tendons.

Stabilizing Factors at Synovial Joints

  1. Shapes of articular surfaces (minor role).

  2. Ligament number and location (limited role).

  3. Muscle tendons crossing the joint (most important):

    • Muscle tone maintains tautness in hip and shoulder joints.

Types of Synovial Joints

  • Classifications based on the shape of articular surfaces include:

    • Plane Joints: Allow gliding movements.

    • Hinge Joints: Uniaxial movement (e.g., elbow).

    • Pivot Joints: Rotation around a single axis (e.g., radius and ulna).

    • Condylar Joints: Biaxial movement (e.g., metacarpophalangeal joint).

    • Saddle Joints: Biaxial movement (e.g., thumb joint).

    • Ball-and-Socket Joints: Multiaxial movement (e.g., shoulder and hip).

Knee Joint

  • Largest and most complex joint in the body, consisting of three joints in one cavity:

    • Femoropatellar joint: Between patella and femur.

    • Medial and Lateral Tibiofemoral joints: Between femur and tibias.

  • Stabilization provided by muscle tendons, including quadriceps and semimembranosus.

  • Various ligaments stabilize the knee:

    • Capsular and Extracapsular ligaments: Prevent hyperextension.

    • Intracapsular ligaments: Enable anterior-posterior stability (e.g., ACL and PCL).

Inflammatory and Degenerative Conditions

  • Arthritis: Over 100 inflammatory or degenerative diseases affecting joints, with symptoms of pain, stiffness, and swelling.

  • Osteoarthritis (OA): Common degenerative arthritis associated with aging and cartilage breakdown. Treatment involves activity, pain relievers, and topical creams.

  • Rheumatoid Arthritis (RA): Autoimmune condition causing inflammation and joint destruction primarily in women aged 40-50. Treatment includes anti-inflammatory medications and possible joint replacement.