Chapter 9

Joints

Articulations

• Definition: A point where two skeletal elements meet.

• Skeletal elements include bones, cartilage, and teeth.

• Study of joints: Arthrology.

• Study of movement: Kinesiology.

• Classification by structure or function.

Classification Based on Function

• Synarthrosis: Immovable joints (syn = together).

• Amphiarthosis: Slightly movable joints (amphi = on both sides).

• Diarthrosis: Freely movable joints (diarthro = double joint).

Classification Based on Structure

• Fibrous Joints:

  • No joint cavity; bones held by fibrous connective tissue.

  • Types: Suture (immovable), Syndesmosis (slightly movable), Gomphosis (immovable).

• Cartilaginous Joints:

  • No joint cavity; bones held by cartilage.

  • Types: Synchondrosis (immovable, e.g., epiphyseal plate, ribs), Symphysis (slightly movable, e.g., intervertebral discs).

• Synovial Joints:

  • Presence of joint cavity, allowing free movement.

  • Examples: Knee, TMJ, shoulder, hip, elbow.

Synovial Joint Structure

• Articular Capsule:

  • Encloses the synovial cavity; unites articulating bones.

  • Consists of a fibrous capsule and synovial membrane.

• Articular Cartilages:

  • Hyaline cartilage covering bone ends.

• Synovial Fluid:

  • Secreted by synovial membrane; lubricates and nourishes articular cartilages.

Accessory Structures in Synovial Joints

• Ligaments: Extracapsular (outside capsule) and intracapsular (within capsule).

• Articular Discs (Menisci): Pads of fibrocartilage enhancing fit and stability.

• Bursae: Reduces friction; inflammation leads to bursitis.

Types of Movements at Synovial Joints

1. Gliding: Back and forth and side to side movements; occurs in wrist and ankle.

2. Angular Movements: Increase or decrease angle between bones (flexion/extending/circumduction).

3. Rotation: Bone revolves around its own long axis.

4. Special Movements: Inversion, eversion, dorsiflexion, plantar flexion, supination, pronation, elevation, depression.

Types of Synovial Joints

1. Planar (Gliding) Joint: Side-to-side movements (e.g., intercarpal joints).

2. Hinge Joint: Flexion/extension movements (e.g., knee, elbow).

3. Pivot Joint: Rotation (e.g., proximal radioulnar joint).

4. Condyloid (Ellipsoid) Joint: Biaxial movement (e.g., wrist).

5. Saddle Joint: Biaxial movement (e.g., thumb).

6. Ball and Socket Joint: Triaxial movement (e.g., shoulder, hip).

Disorders of Joints

• Arthritis:

  • Osteoarthritis: Wear and tear, degeneration of cartilage.

  • Gouty Arthritis: Urate crystals cause joint inflammation.

  • Rheumatoid Arthritis: Autoimmune disorder attacking cartilages.

• Other Disorders:

  • Lyme disease: Bacterial joint infection.

  • Ankylosing spondylitis: Affects vertebrae joints.

  • Ankle sprains: Treated with RICE (rest, ice, compression, elevation).

Aging and Joints

• Decreased synovial fluid production.

• Thinning cartilage.

• Loss of ligament length and flexibility.

• Arthroscopy: Minimally invasive joint examination and repair.

• Arthroplasty: Joint replacement surgery (often hip, knee, shoulder).