5. CLASSIFICATION, TYPES AND MOVEMENTS OF JOINTS, DISORDERS OF JOINTS

Introduction

A joint (also called an articulation) is a point where two or more bones meet.
Joints make our body flexible, allowing different types of movements like bending, rotation, and stretching.
They also help maintain body posture and balance.

Classification of Joints

Joints can be classified based on structure and function.

A. Structural Classification

1. Fibrous Joints (Synarthroses)
   • Bones are joined by fibrous connective tissue.
   • No joint cavity and no movement.
   • Examples: Sutures of the skull, teeth sockets.
2. Cartilaginous Joints (Amphiarthroses)
   • Bones are connected by cartilage.
   • Allow slight movement.
   • Examples: Between vertebrae, pubic symphysis.
3. Synovial Joints (Diarthroses)
   • Freely movable joints.
   • Have a joint cavity filled with synovial fluid.
   • Enclosed by a capsule and supported by ligaments.
   • Examples: Shoulder, knee, hip, elbow.

Original Notes:

B. Functional Classification

Based on the degree of movement, joints are classified as:

1. Immovable (Synarthrosis): No movement (e.g., skull sutures).
2. Slightly Movable (Amphiarthrosis): Limited movement (e.g., vertebral joints).
3. Freely Movable (Diarthrosis): Wide range of movements (e.g., shoulder joint).

Structure of a Synovial Joint

A synovial joint has the following main parts:

• Articular Cartilage: Smooth covering on bone ends that reduces friction.
• Synovial Cavity: Space filled with synovial fluid that lubricates the joint.
• Synovial Fluid: Nourishes cartilage and reduces wear.
• Joint Capsule: Outer fibrous covering that encloses the joint.
• Ligaments: Strong bands that connect bones and stabilize the joint.
• Bursae: Fluid-filled sacs that reduce friction between tendons and bones.

Types of Synovial Joints and Their Movements

1. Ball and Socket Joint
   • Round end of one bone fits into the cup-shaped cavity of another.
   • Allows movement in all directions — rotation, abduction, adduction, flexion, extension.
   • Examples: Shoulder, hip joints.
2. Hinge Joint
   • Movement only in one direction (like a door hinge).
   • Examples: Elbow, knee, ankle joints.
3. Pivot Joint
   • One bone rotates around another.
   • Example: Joint between atlas and axis (neck rotation).
4. Gliding (Plane) Joint
   • Flat bone surfaces slide over one another.
   • Examples: Wrist (carpal bones), ankle joints.
5. Condyloid (Ellipsoid) Joint
   • Oval surface fits into an elliptical cavity — allows movement in two planes.
   • Examples: Wrist joint, between skull and first vertebra.
6. Saddle Joint
   • Both bones have concave and convex surfaces like a saddle.
   • Example: Thumb joint (carpometacarpal joint).

Types of Movements at Joints

1. Flexion: Bending a joint (e.g., bending elbow).
2. Extension: Straightening a joint (e.g., straightening leg).
3. Abduction: Moving a limb away from the body (e.g., raising arm sideways).
4. Adduction: Moving a limb toward the body.
5. Rotation: Turning a bone around its axis (e.g., head movement).
6. Circumduction: Circular movement of a limb (e.g., arm circles).
7. Supination: Turning palm upward.
8. Pronation: Turning palm downward.
9. Elevation: Lifting a part upward (e.g., shrugging shoulders).
10. Depression: Moving a part downward.

Disorders of Joints

1. Arthritis:
   Inflammation of joints causing pain, swelling, and stiffness.
   • Types:
     • Osteoarthritis: Due to wear and tear of cartilage (common in old age).
     • Rheumatoid arthritis: Autoimmune condition where body attacks joint lining.
2. Gout:
   Deposition of uric acid crystals in joints (commonly affects big toe).
3. Dislocation:
   Bones are forced out of their normal joint position (common in shoulder).
4. Sprain:
   Stretching or tearing of ligaments around a joint.
5. Bursitis:
   Inflammation of the bursae due to friction or infection.
6. Ankylosis:
   Abnormal stiffness and immobility of a joint due to fusion of bones.