Study Notes on Joints from Marieb Human Anatomy & Physiology

Chapter 08: Joints

Importance of Understanding Joints

  • Why This Matters: Knowledge of joints is crucial in treating patient injuries, such as ankle sprains.

Classification of Joints

8.1 Definitions

  • Joints (Articulations): Locations where two or more bones meet.

  • Functions of Joints:

    • Provide mobility to the skeleton.

    • Hold the skeleton together.

  • Two Main Classifications:

    1. Structural Classification: Based on material binding joints and presence/absence of joints.

    • Types:

      • Fibrous Joints

      • Cartilaginous Joints

      • Synovial Joints

    1. Functional Classification: Based on movement capabilities.

    • Types:

      • Synarthroses: Immovable joints.

      • Amphiarthroses: Slightly movable joints.

      • Diarthroses: Freely movable joints.

  • Note: Structural classifications are considered more definitive for this context.

8.2 Fibrous Joints

  • Definition: Bones connected by dense fibrous connective tissue with no joint cavity, most are immovable.

  • Types of Fibrous Joints:

    1. Sutures: Rigid joints found in the skull with interlocking bones allowing for growth during youth.

    • In middle age, sutures ossify and become immovable (synostoses).

    1. Syndesmoses: Bones connected by ligaments with variable movement:

    • Examples:

      • Short fibers (little to no movement): Inferior tibiofibular joint.

      • Longer fibers: Interosseous membrane between radius and ulna.

    1. Gomphoses: Peg-in-socket joints, seen in teeth held in their sockets by periodontal ligaments.

8.3 Cartilaginous Joints

  • Definition: Bones united by cartilage, similarly lacking a joint cavity and are not highly movable.

  • Types:

    1. Synchondroses: Bones united by hyaline cartilage, mostly immovable.

    • Examples:

      • Epiphyseal plate joints.

      • Cartilage of the first rib with sternum.

    1. Symphyses: Bones united by fibrocartilage, slightly movable.

    • Examples:

      • Intervertebral joints.

      • Pubic symphysis.

8.4 Synovial Joints

  • Definition: These joints separate bones with a fluid-filled cavity and are all diarthrotic (freely movable).

  • Characteristics:

    • Six general features:

    1. Articular Cartilage: Hyaline cartilage covering bone ends to prevent damage.

    2. Joint (Synovial) Cavity: Unique small fluid-filled space.

    3. Articular (Joint) Capsule: Two layers:

      • Outer fibrous layer: Dense irregular connective tissue.

      • Inner synovial membrane: Loose connective tissue producing synovial fluid.

    4. Synovial Fluid: Viscous fluid that lubricates and nourishes cartilage, containing immune cells.

    5. Reinforcing Ligaments:

      • Capsular Ligaments: Thickened areas of the fibrous layer.

      • Extracapsular Ligaments: Located outside of the capsule.

      • Intracapsular Ligaments: Deep to the capsule and covered by synovial membrane.

    6. Nerves and Blood Vessels: Nerves detect pain and monitor position; blood vessels supply synovial fluid.

    • Additional features include fatty pads and articular discs (menisci).

Bursae and Tendon Sheaths

  • Bursae: Bags of synovial fluid acting as lubricating “ball bearings” to reduce friction.

  • Tendon Sheaths: Elongated bursae encasing tendons under friction.

Stability Influencing Factors

  • Factors determining synovial joint stability:

    1. Articular Surface Shape: E.g., shallow surfaces are less stable (minor role).

    2. Ligament Number and Location: More ligaments provide stronger support (limited role).

    3. Muscle Tone: Maintains tension on tendons across joints (most important for stability in shoulder and knee).

Movements Allowed by Synovial Joints

General Types of Movement

  1. Nonaxial Movement: Gliding movements only.

  2. Uniaxial Movement: Movement in one plane only.

  3. Biaxial Movement: Movement in two planes.

  4. Multiaxial Movement: Movement across all three planes.

  5. Types of Movements:

    • Gliding: Flat bone surfaces glide over one another.

      • Examples: Intercarpal joints.

    • Angular Movements: Alter angles between bones:

    1. Flexion: Decreases joint angle.

    2. Extension: Increases joint angle.

    3. Hyperextension: Movement beyond anatomical position.

    4. Abduction: Movement away from midline.

    5. Adduction: Movement towards midline.

    6. Circumduction: Circular movement of limb or finger.

    • Rotation: Rotation of a bone around its own axis:

    1. Medial Rotation: Toward midline.

    2. Lateral Rotation: Away from midline.

    • Special Movements: Include supination, pronation, dorsiflexion, plantar flexion, inversion, eversion, elevation, depression, protraction, and retraction.

Types of Synovial Joints

  1. Plane Joint: Flattest surfaces; allow gliding movements.

    • Examples: Intercarpal joints.

  2. Hinge Joint: Cylinder-in-trough shape; uniaxial movement for flexion and extension.

    • Examples: Elbow joint.

  3. Pivot Joint: Sleeve and axle structure; uniaxial rotation allowed.

    • Examples: Proximal radioulnar joints.

  4. Condylar Joint: Oval surfaces allow biaxial movement.

    • Examples: Knuckle joints.

  5. Saddle Joint: Concave and convex surface shapes; allow biaxial movement.

    • Example: Carpometacarpal joint of the thumb.

  6. Ball-and-Socket Joint: Spherical head-into-cup depression; multiaxial movement.

    • Examples: Shoulder and hip joints.

Selected Synovial Joints

Temporomandibular Joint (TMJ)

  • Definition: Modified hinge joint between mandibular condyle and temporal bone with two movements:

    1. Hinge Movement: Depression and elevation of the mandible.

    2. Gliding Movement: Side-to-side motions.

  • Clinical Notes: TMJ dislocation is common due to shallow socket; may lead to various symptoms including pain and stiffness.

Shoulder Joint

  • Definition: Glenohumeral joint; most freely moving but least stable due to ball-and-socket feature.

  • Structure: Thin articular capsule with a fibrocartilaginous glenoid labrum enhancing stability.

  • Ligaments Involved: Supportive ligaments are primarily anterior; include coracohumeral and glenohumeral ligaments.

  • Muscle Contributions: Rotator cuff muscles provide significant joint stability.

Elbow Joint

  • Definition: Hinge joint primarily between humerus and both radius and ulna.

  • Function: Permit flexion and extension only; supported by the anular ligament and collateral ligaments.

Hip Joint

  • Definition: Coxal joint; ball-and-socket structure with a deep acetabulum for stability; less prone to dislocation.

  • Reinforcing Structures: Various ligaments provide stability but play a limited role during hip movement.

Knee Joint

  • Definition: Largest and most complex joint, consisting of three joints in a single cavity.

  • Structure: Includes the femoropatellar joint, lateral joint, and medial joint. Has critical anatomy including menisci and numerous ligaments.

  • Clinical Notes: Known for injuries termed “Unhappy Triad.” Vulnerable to horizontal blows affecting major ligaments and cartilage.

Disorders of Joints

Common Joint Injuries

  1. Cartilage Tears: Caused by compression; healing is challenging; surgical intervention may include meniscectomy.

  2. Sprains: Ligament injuries characterized by stretching/torn ligaments; treatment can include surgical repair or immobilization.

  3. Dislocations: Alignment loss; treatment involves reduction of the joint.

Inflammatory and Degenerative Conditions

  1. Bursitis: Inflammation induced by friction; managed by rest and pain relief.

  2. Tendonitis: Overuse inflammatory condition; treated similarly to bursitis.

  3. Arthritis: >100 types damaging joints; symptoms include pain and swelling; types include osteoarthritis, rheumatoid arthritis, etc.

  4. Osteoarthritis: “Wear-and-tear” arthritis with aging and cartilage breakdown; treatment involves lifestyle changes and pain management.

  5. Rheumatoid Arthritis: Autoimmune condition leading to joint damage; treatment may involve drug therapy and surgery.

  6. Gouty Arthritis: Caused by uric acid crystal buildup; management includes medication and dietary changes.

  7. Lyme Disease: Bacterial infections leading to joint issues; treated with antibiotics.

Developmental Aspects of Joints

  • Joint structures generally resemble adult forms by embryonic week 8.

  • Joint health can be affected by use; increased activity can strengthen joint stability over time.