Lecture 9 notes & study guide

1. Classification of Body Joints

Joints (articulations) are sites where two or more bones meet. They are classified both functionally and structurally.

1.1 Functional Classification

Based on the amount of movement allowed at the joint:

Synarthroses: Immovable joints.
- Examples: Sutures of the skull.
Amphiarthroses: Slightly movable joints.
- Examples: Pubic symphysis, intervertebral discs.
Diarthroses: Freely movable joints.
- Examples: Shoulder, hip, knee, elbow joints. All diarthroses are synovial joints.

1.2 Structural Classification

Based on the material binding the bones and the presence or absence of a joint cavity:

Fibrous Joints: Bones joined by fibrous connective tissue; no joint cavity; most are synarthrotic (immovable).
- Sutures: Seams between bones of the skull. During middle age, they ossify and fuse, becoming synostoses (bony junctions).
  - Example: Coronal suture, sagittal suture.
- Syndesmoses: Bones connected by a ligament, cord, or band of fibrous tissue. Amount of movement varies.
  - Example: Ligament connecting tibia and fibula (immovable); interosseous membrane between radius and ulna (slightly movable).
- Gomphoses: Peg-in-socket fibrous joint.
  - Example: Articulation of a tooth with its alveolar socket.
Cartilaginous Joints: Bones united by cartilage; no joint cavity; not highly movable.
- Synchondroses: Bar or plate of hyaline cartilage unites bones; virtually all are synarthrotic.
  - Example: Epiphyseal plates in children (temporary), joint between costal cartilage of first rib and sternum.
- Symphyses: Articular surfaces covered with articular (hyaline) cartilage, which is then fused to an intervening pad of fibrocartilage. Amphiarthrotic (slightly movable).
  - Example: Pubic symphysis, intervertebral discs.
Synovial Joints: Bones separated by a fluid-filled joint cavity; all are diarthrotic (freely movable).
- Characteristic features:
  1. Articular Cartilage: Hyaline cartilage covers the ends of bones, providing a smooth, frictionless surface.
  2. Joint (Articular) Cavity: A potential space containing synovial fluid.
  3. Articular Capsule: Two layers.
    - Fibrous layer: Outer layer of dense irregular connective tissue, continuous with periosteum.
    - Synovial membrane: Inner layer of loose connective tissue, produces synovial fluid.
  4. Synovial Fluid: Viscous, slippery fluid that lubricates and nourishes articular cartilage.
  5. Reinforcing Ligaments: Capsular (intrinsic), extracapsular, or intracapsular ligaments strengthen the joint.
  6. Nerves and Blood Vessels: Nerves detect pain and joint position; blood vessels supply the synovial membrane.
- Additional features:
  - Articular discs (menisci): Pads of fibrocartilage (e.g., in knee, temporomandibular joint) that improve fit, reduce wear, and absorb shock.
  - Bursae: Flattened fibrous sacs lined with synovial membrane, containing synovial fluid, reduce friction where ligaments, muscles, skin, tendons, or bones rub together.
  - Tendon Sheaths: Elongated bursae that wrap around a tendon subjected to friction.
- Types of Synovial Joints (based on shape of articular surfaces and movement allowed):
  - Plane joints: Flat articular surfaces, allow short gliding movements. Example: Intercarpal joints, intertarsal joints.
  - Hinge joints: Cylindrical projection of one bone fits into a trough-shaped surface on another, allow flexion and extension. Example: Elbow joint, knee joint, interphalangeal joints.
  - Pivot joints: Rounded end of one bone fits into a sleeve (bone or ligament) of another, allow rotation. Example: Atlantoaxial joint, proximal radioulnar joint.
  - Condylar (ellipsoidal) joints: Oval articular surface of one bone fits into an oval depression in another, allow all angular movements (flexion, extension, abduction, adduction, circumduction). Example: Radiocarpal (wrist) joints, metacarpophalangeal (knuckle) joints.
  - Saddle joints: Articular surfaces have both concave and convex areas, shaped like a saddle, allow greater freedom of movement than condylar joints. Example: Carpometacarpal joint of the thumb.
  - Ball-and-socket joints: Spherical head of one bone fits into a cup-like socket of another, allow most freedom of movement (flexion, extension, abduction, adduction, rotation, circumduction). Example: Shoulder joint, hip joint.

2. Body Movements

2.1 General Movements

Flexion: Decreases the angle of a joint (e.g., bending elbow).
Extension: Increases the angle of a joint (e.g., straightening elbow).
Hyperextension: Excessive extension beyond anatomical position (e.g., looking up at the sky).
Abduction: Movement of a limb away from the midline of the body (e.g., raising arm sideways).
Adduction: Movement of a limb toward the midline of the body (e.g., lowering arm to side).
Circumduction: Movement of a limb so that it describes a cone in space; combination of flexion, extension, abduction, and adduction (e.g., rotating arm in a circle).
Rotation: Turning of a bone around its own long axis.
- Medial (internal) rotation: Toward the midline (e.g., turning arm inward).
- Lateral (external) rotation: Away from the midline (e.g., turning arm outward).

2.2 Special Movements

Pronation: Forearm rotates medially, palm faces posteriorly or inferiorly.
Supination: Forearm rotates laterally, palm faces anteriorly or superiorly (anatomical position).
Dorsiflexion: Lifting the foot superiorly toward the shin.
Plantarflexion: Depressing the foot (pointing the toes).
Inversion: Sole of the foot turns medially.
Eversion: Sole of the foot turns laterally.
Protraction: Non-angular anterior movement (e.g., jutting out the jaw).
Retraction: Non-angular posterior movement (e.g., pulling jaw back).
Elevation: Lifting a body part superiorly (e.g., shrugging shoulders).
Depression: Moving a body part inferiorly (e.g., lowering shoulders).
Opposition: Movement of the thumb to touch the tips of other fingers.

3. Structure and Movements of Specific Body Joints

3.1 Shoulder Joint (Glenohumeral Joint)

Type: Ball-and-socket joint.
Structure: Head of the humerus articulates with the glenoid cavity of the scapula. It is the most freely moving joint, but also the most unstable.
- Stability: Sacrificed for mobility, primarily due to rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis) and associated tendons.
- Ligaments: Coracohumeral ligament, three glenohumeral ligaments.
- Glenoid labrum: Rim of fibrocartilage that deepens the glenoid cavity.
Movements: Flexion, extension, hyperextension, abduction, adduction, medial and lateral rotation, circumduction.

3.2 Elbow Joint

Type: Hinge joint (primarily).
Structure: Formed by the articulation of the trochlea of the humerus with the trochlear notch of the ulna, and the capitulum of the humerus with the head of the radius.
- Stability: Medial (ulnar collateral) and lateral (radial collateral) ligaments provide strong reinforcement.
- Annular ligament: Encompasses the head of the radius, securing it to the ulna.
Movements: Primarily flexion and extension. The radioulnar joints allow pronation and supination of the forearm.

3.3 Hip Joint (Coxal Joint)

Type: Ball-and-socket joint.
Structure: Head of the femur articulates with the acetabulum of the pelvic bone. Designed for weight-bearing and stability.
- Stability: Deep acetabular socket, reinforced by the acetabular labrum (fibrocartilage rim), and powerful ligaments (iliofemoral, pubofemoral, ischiofemoral).
Movements: Flexion, extension, abduction, adduction, medial and lateral rotation, circumduction.

3.4 Knee Joint

Type: Largest and most complex joint; primarily a hinge joint, but also allows some rotation when flexed.
Structure: Articulations between the femur and tibia (femorotibial joint) and the patella and femur (femoropatellar joint).
- Menisci: Medial and lateral menisci (C-shaped fibrocartilage) improve congruency between femur and tibia, absorb shock.
- Ligaments:
  - Extracapsular: Patellar ligament, medial (tibial) collateral ligament, lateral (fibular) collateral ligament.
  - Intracapsular: Anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) cross within the joint capsule, preventing anterior/posterior displacement of tibia relative to femur.
Movements: Primarily flexion and extension. Some rotation is possible when the knee is flexed.

4. Common Joint Injuries and Disorders

4.1 Injuries

Sprains
- Cause: Ligaments reinforcing a joint are stretched or torn. Common in ankle, knee, and lumbar region of spine.
- Symptoms: Pain, swelling, bruising, instability of the joint.
- Treatment: RICE (Rest, Ice, Compression, Elevation) for mild sprains. Severe tears may require surgical repair or immobilization.
Strains
- Cause: Overstretching or tearing of muscles or tendons.
- Symptoms: Pain, muscle spasms, swelling, limited range of motion.
- Treatment: RICE, pain relievers. Severe tears may require surgery.
Dislocation (Luxation)
- Cause: Bones forced out of alignment at a joint. Often accompanied by sprains, inflammation, and difficulty moving the joint.
- Location: Common in shoulder, fingers, thumb, and jaw.
- Symptoms: Severe pain, deformity of the joint, inability to move.
- Treatment: Reduction (bones returned to proper position) by a medical professional, followed by immobilization.
Cartilage Tears
- Cause: Often due to high-impact trauma, usually to the menisci of the knee; common in athletes.
- Symptoms: Pain, clicking or popping sound, joint locking, instability.
- Treatment: Arthroscopic surgery to remove or repair the torn cartilage. Cartilage itself is avascular and rarely heals spontaneously.

4.2 Disorders

Bursitis
- Cause: Inflammation of a bursa, usually caused by a blow or friction.
- Location: Common in shoulder, knee (housemaid's knee, olecranon bursitis).
- Symptoms: Pain, swelling, redness over the affected joint.
- Treatment: Rest, ice, anti-inflammatory drugs. Aspiration of fluid or injection of corticosteroids may be necessary.
Tendonitis
- Cause: Inflammation of tendon sheaths, typically caused by overuse.
- Location: Common around shoulder, elbow (tennis elbow), wrist, and ankle.
- Symptoms: Pain and tenderness, especially with movement, swelling.
- Treatment: Rest, ice, anti-inflammatory drugs.
Arthritis (Inflammation of the joint)
- Symptoms (general): Pain, stiffness, and swelling of a joint.
- Osteoarthritis (OA): Most common chronic arthritis, often called "wear-and-tear arthritis."
  - Cause: Breakdown of articular cartilage due to normal aging, genetic factors, or excessive joint stress. As cartilage erodes, bones rub together, forming bone spurs (osteophytes).
  - Location: Common in weight-bearing joints (knees, hips, lumbar spine) and hands.
  - Symptoms: Slow onset, joint stiffness (especially in the morning or after rest), pain that worsens with activity and eases with rest, crepitus (grating sound).
  - Treatment: Pain relievers, anti-inflammatory drugs, exercise, weight loss, physical therapy. Joint replacement surgery (arthroplasty) for severe cases.
- Rheumatoid Arthritis (RA): Chronic, inflammatory, autoimmune disease.
  - Cause: Immune system attacks the body's own tissues, specifically the synovial membrane, leading to inflammation, joint destruction, and eventual ankylosis (fusion of bones).
  - Location: Usually affects smaller joints bilaterally (e.g., fingers, wrists, ankles, feet), but can involve larger joints.
  - Symptoms: Gradual onset, joint tenderness, stiffness (often severe in the morning), swelling, pain, fatigue, fever, anemia. Can lead to joint deformities.
  - Treatment: No cure. Immunosuppressants (e.g., methotrexate), NSAIDs, corticosteroids, biological response modifiers. Physical therapy to maintain joint function.
- Gouty Arthritis (Gout): Inflammatory arthritis.
  - Cause: Deposition of uric acid crystals in joints and soft tissues, followed by inflammation. Uric acid is a waste product of nucleic acid metabolism.
  - Location: Typically affects one joint, most commonly the base of the great toe, but can also affect knees, heels, wrists, and fingers.
  - Symptoms: Sudden onset of excruciating pain, swelling, redness, and tenderness, often at night.
  - Treatment: Anti-inflammatory drugs (NSAIDs, corticosteroids), colchicine during acute attacks. Lifestyle changes (dietary restrictions of purine-rich foods, alcohol), medications to lower uric acid levels (e.g., allopurinol) for long-term management.
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