Skeletal System Articulations and Disorders

Introduction to Articulations

• Definition: Articulations are the site where two or more bones meet.
• Vulnerability: Joints are considered the weakest part of the skeleton.

Functional Classification of Joints

Joints are classified functionally based on the amount of movement they allow:

• Synarthroses: These are categorized as immovable joints.
• Amphiarthrosis: These are categorized as slightly movable joints.
• Diarthroses: These are categorized as fully movable joints.

Structural Classification of Joints

Joints are classified structurally based on the material that binds the bones together.

1. Fibrous Joints

In fibrous joints, the bone ends are united by collagenic fibers. There are three types:

• Sutures: Fibrous joints found in the skull.
• Syndesmoses:
  • The joint is held together by a ligament.
  • The fibrous tissue can vary in length but is generally longer than the tissue found in sutures.
  • Example: The joint between the fibula and the tibia.
• Gomphoses:
  • Ligaments hold the tooth in its bony socket.
  • This is an immovable joint.
  • Anatomical Components:
    • Enamel
    • Dentin
    • Gum
    • Pulp
    • Root of tooth
    • Socket of alveolar process
    • Periodontal ligament (membrane)

2. Cartilaginous Joints

In these joints, the bones are united by cartilage. They lack a synovial cavity and can be amphiarthrosis (slightly movable) or synarthrosis (immovable).

• Bonds: Bones are connected by fibrocartilage or hyaline cartilage.
• Types:
  • Synchondrosis: Bones united by hyaline cartilage.
  • Symphyses: Bones united by fibrocartilage.

3. Synovial Joints

Synovial joints are characterized by the presence of a synovial cavity and are generally diarthrotic (freely movable).

Specific Types of Synovial Joints

• Planar Joint:

  • Structure: Bone surfaces are slightly curved.
  • Movement: Allows side-to-side movement only; rotation is prevented by ligaments.
  • Examples: Intercarpal to intertarsal joints, sternoclavicular joint, and vertebrocostal joints.

• Hinge Joint:

  • Structure: The convex surface of one bone fits into the concave surface of a second bone.
  • Movement: Uniaxial (like a door hinge). Movements produced include flexion, extension, and hyperextension.
  • Examples: Knee, elbow, ankle, and interphalangeal joints.

• Pivot Joint:

  • Structure: The rounded surface of one bone articulates with a ring formed by a second bone and a ligament.
  • Movement: Monoaxial; only allows rotation around a longitudinal axis.
  • Examples:
    • Proximal radioulnar joint (allows supination and pronation).
    • Atlanto-axial joint (allows turning the head side to side to signal "no").

• Saddle Joint:

  • Structure: One bone is saddle-shaped, and the other bone fits like a person riding on that saddle.
  • Movement: Biaxial.
    • Circumduction: Allows the tip of the thumb to travel in a circle.
    • Opposition: Allows the thumb to touch the tips of other fingers.
  • Example: Trapezium of the carpus and metacarpal of the thumb.

• Ball & Socket Joint:

  • Structure: A ball fitting into a cup-like depression.
  • Movement: Multiaxial. Includes flexion/extension, abduction/adduction, and rotation.
  • Examples: Shoulder joint and hip joint.

• Condyloid (Ellipsoid) Joint:

  • Structure: An oval-shaped depression fits into another oval depression.
  • Movement: Biaxial. Flexion/extension and abduction/adduction are possible.
  • Examples: Wrist and metacarpophalangeal joints for digits $2$ to $5$.

Anatomy and Mechanics of Specific Joints

The Knee Joint and Cruciate Ligaments

• Cruciate ligaments prevent undesirable movements at the knee joint.
• Anterior Cruciate Ligament (ACL): When the knee is flexed or extended, the anterior cruciate prevents anterior slipping movements of the tibia.

Temporomandibular Joint (Complex Joint)

• Contains an articular disc.
• Features gliding movement above the disc and hinge movement below the disc.
• Movements: Depression, elevation, protraction, and retraction.

Glossary of Body Movements

• Flexion: Decreasing the angle of a joint (e.g., bent knee).
• Extension: Increasing the angle of a joint (e.g., extend knee).
• Hyperextension: Continuation of extension beyond the anatomical position (e.g., bringing the leg back).
• Dorsi flexion: Lifting the foot toward the shin (heel movement).
• Plantar flexion: Depressing the foot (toe movement).
• Abduction: Movement of a limb away from the midline (e.g., leg out).
• Adduction: Movement of a limb toward the midline (e.g., leg in).
• Rotation: Twisting motion of a bone around its own axis (can be medial or lateral).
• Circumduction: Moving a limb so that it describes a cone in space (circular motion).
• Supination: Rotating the forearm so the palm faces up (radius and ulna are parallel).
• Pronation: Rotating the forearm so the palm faces down (radius rotates over the ulna).
• Eversion: Turning the sole of the foot outward.
• Inversion: Turning the sole of the foot inward.
• Protraction: Moving a body part forward in a transverse plane (e.g., chin forward).
• Retraction: Moving a body part backward in a transverse plane (e.g., chin back).
• Elevation: Lifting a body part superiorly (e.g., shoulders up).
• Depression: Moving a body part inferiorly (e.g., shoulders down).

Clinical Disorders and Diseases

• Bursitis: Inflammation of a bursa.
• Tendonitis: Inflammation of tendon sheaths.
• Lyme Disease: An inflammatory disease caused by bacteria.
• Ankle Sprains and Fractures.
• Osteoarthritis (OA):
  • Degenerative joint disease associated with aging and wear and tear.
  • Non-inflammatory: Only the cartilage is affected, not the synovial membrane.
  • Deterioration of cartilage produces bone spurs, which restrict movement.
  • Symptom: Pain upon awakening that disappears with movement.
• Gouty Arthritis (Gout):
  • Caused by the buildup of uric crystals in joints, leading to pain.
  • Uric acid is a waste product of $DNA$ and $RNA$ metabolism.
  • Uric acid builds up in the blood and is deposited in cartilage, causing inflammation and swelling.
  • In advanced stages, bones may fuse.
  • Primarily affects middle-aged men with an abnormal gene.
• Rheumatoid Arthritis (RA):
  • An autoimmune disorder where the immune system attacks the cartilage.
  • Results in inflammation, swelling, and pain.
  • The final step of the disease is the fusion of the joint.

Medical Procedures and Examinations

• Arthroscopy:
  • Examination of a joint using an instrument the size of a pencil.
  • Used to remove torn knee cartilage through small incisions.
• Arthroplasty:
  • Replacement of joints.
  • Total Hip Replacement: Replaces the acetabulum and the head of the femur using a plastic socket and a metal head.
  • Knee Replacement: A common procedure to restore joint function.

Questions & Discussion

• Question 1: What is a meniscus?
• Question 2: Demonstrate adduction.
• Question 3: What does the acronym RICE stand for?
• Question 4: What type of joint is a synovial joint?
• Question 5: Where is a planar joint found?
• Question 6: Why is it a good idea to warm up before running?
• Question 7: What is gout?
• Question 8: What causes Lyme disease?