Ch 9

Anatomy of Joints

Introduction to Joints

  • Definition: Joints are the connections between bones in the body.

  • Greek Root: "arthro" indicating joint.

  • Focus: The classification and function of joints, types of movement.

Classification of Joints

  • Joints are classified based on:

    • Function they serve.

    • Type of movement allowed.

Functional Classification

  1. Synarthrosis (Immovable Joints)

    • Location: Primarily found in the axial skeleton.

    • Characteristics: Not exclusively, as other joint types can be present.

  2. Amphiarthrosis (Slightly Movable Joints)

    • Location: Common in axial skeleton.

  3. Diarthroses (Freely Movable Joints)

    • Location: Most frequent in the appendicular skeleton.

    • Characteristics: All synovial joints are classified as diarthrotic.

Structural Classification

  • Joints can also be classified based on the material binding them:

    1. Fibrous

    2. Cartilaginous

    3. Synovial

1. Fibrous Joints

  • Types of Fibrous Joints: Depends on fiber length and type.

    • Sutures: Short fibers (e.g., skull bones).

    • Function: Allow for bone growth as brain expands during childhood.

    • Closure in middle age leads to synostoses (ossification).

    • Syndesmoses: Longer fibers providing slight mobility (e.g., tibiofibular joint).

    • Example: Radius and ulna can move; tibia/fibula are mostly immobile.

    • Gomphoses: Periodontal ligaments stabilizing teeth in gums.

2. Cartilaginous Joints

  • Types of Cartilaginous Joints:

    • Synchondroses: Hyaline cartilage (e.g., epiphyseal plates, sternum-rib connection).

    • Symphyses: Fibrocartilage, allows slight movement (e.g., intervertebral discs, pubic symphysis).

  • Both types lack a joint cavity.

3. Synovial Joints

  • Characteristics:

    • Contain a joint cavity filled with synovial fluid.

    • Opposing bones covered with hyaline cartilage.

    • Described by type of movement:

    1. Plane Joints: Flat surfaces sliding over each other (e.g., between tarsals).

    2. Hinge Joints: Allows flexion and extension (e.g., elbow).

    3. Pivot Joints: Bone rotation around an axis (e.g., proximal radioulnar joint).

    4. Condylar (Ellipsoid) Joints: Movement along two axes (e.g., wrist joints).

    5. Saddle Joints: Concave and convex surfaces leading to biaxial movements (e.g., thumb).

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

Synovial Joint Structures

  • Articular Capsule: Comprises a dense fibrous outer layer and synovial membrane.

    • Synovial Fluid: Cushions joints, derived from blood and composed of glycoproteins produced by fibroblasts.

    • Ligaments: Reinforce joints, can be intracapsular or extracapsular.

    • Bursae: Fluid-filled sacs to reduce friction (e.g., between tendons and bones).

    • Tendon Sheaths: Specialized bursae wrapping around tendons.

Types of Joint Movements

  • Movements in Synovial Joints Include:

    • Gliding Movements: Flat surfaces sliding (e.g., wrist).

    • Angular Movements: Changing angle between bones.

    1. Flexion: Decreasing angle (e.g., bending elbow).

    2. Extension: Increasing angle (e.g., straightening arm).

    3. Abduction: Moving away from body center.

    4. Adduction: Moving toward body center.

    5. Circumduction: Circular movement.

    • Rotation: Turning around an axis (e.g., head and legs).

    • Special Movements:

    • Pronation/Supination: Rotating forearm, palm orientation.

    • Opposition: Touching thumb to other fingers.

    • Inversion/Eversion: Movements of the foot.

    • Dorsiflexion/Plantar Flexion: Foot movement toward or away from shin.

Joint Stability and Movement

  • Stability Factors:

    • Shape of articulate surfaces plays a role, but not a strong factor except in specific joints (hip, elbow).

    • Ligaments and muscle tone significantly contribute.

  • Muscle tone involves tension on tendons stabilizing joints.

Specific Joints and Movements

  • Shoulder Joint (Glenohumeral Joint): Most movable, but lacks stability due to loose capsule.

  • Elbow Joint: Classic hinge joint allowing flexion and extension.

  • Knee Joint: Complex and allows rotation; considered compound with menisci.

    • Ligaments in Knee: Cruciate ligaments (anterior and posterior) prevent unwanted sliding motions.

Disorders of Joints

  • Torn cartilage, sprains, dislocations.

  • Inflammatory conditions: Bursitis, tendinitis.

  • Degenerative conditions: Osteoarthritis, rheumatoid arthritis, gouty arthritis, Lyme disease.

Joint Function Throughout Life

  • Joints develop from mesenchyme with joint capsules and cavities forming.

  • Aging may lead to increased arthritis and similar degenerative issues.

Conclusion

  • Next lecture will focus on skeletal muscle tissues, emphasizing muscle structure, origin, and insertion.

  • Upcoming assessments include lab practicums and exams as outlined in the syllabus.