Anatomy of Joints in the Human Body

Introduction

• Joints: Connections between two bones in the skeleton.
• Classification Criteria:
  • Structure
  • Mobility
  • Range of Motion

Structural Classification

1. Synovial Joints

   • Most common type of joint.
   • Surrounded by an articular capsule:
     • Outer fibrous layer: Stabilizes the joint.
     • Inner synovial layer: Secretes synovial fluid for lubrication.
   • Articular surfaces covered in hyaline cartilage (articular cartilage).
   • Additional structures:
     • Articular discs (e.g., knee joint menisci).
     • Bursae: Small sacs reducing friction.
   • Subclassifications:
     • Ball and socket, hinge, pivot, condylar, saddle, and plane joints.

2. Fibrous Joints

   • Connected by tough, fibrous connective tissue.
   • Types:
     • Sutures: Found between skull bones (e.g., coronal suture).
     • Gomphoses: Teeth roots articulated with dental alveoli.
     • Syndesmoses: Ligaments and membranes hold bones (e.g., interosseous membrane between radius and ulna).

3. Cartilaginous Joints

   • Bones connected by fibrocartilage or hyaline cartilage.
   • Types:
     • Synchondroses: Bones connected by hyaline cartilage (e.g., growth plates in long bones).
     • Symphysis: Bones connected by fibrocartilage (e.g., pubic symphysis).

Mobility Classification

• Diarthrosis: Freely mobile joint (e.g., knee joint).
• Amphiarthrosis: Slightly mobile joint (e.g., pubic symphysis).
• Synarthrosis: Immobile joint (e.g., skull sutures).

Range of Motion Classification

• Axes of Movement:
  • Sagittal, frontal, vertical.
• Types:
  • Uniaxial: Hinge and pivot joints.
  • Biaxial: Condylar and saddle joints.
  • Polyaxial/Multiaxial: Ball and socket joints.

Detailed Joint Types

1. Ball and Socket Joint

   • Polyaxial, highly mobile.
   • Examples: Hip (acetabulofemoral) and shoulder (glenohumeral) joints.

2. Hinge Joint

   • Uniaxial, allows flexion and extension.
   • Examples: Knee (tibiofemoral) and elbow joints.

3. Pivot Joint

   • Uniaxial, allows rotation.
   • Example: Atlanto-axial joint.

4. Condylar Joint

   • Biaxial, allows multiple movements.
   • Example: Wrist (radiocarpal) joint.

5. Saddle Joint

   • Biaxial, unique articulation.
   • Example: Carpometacarpal joint of the thumb.

6. Plane Joint

   • Allows sliding or gliding movements.
   • Example: Acromioclavicular joint.

Joint Stability

• Factors Influencing Stability:
  • Degree of contact between surfaces.
  • Presence of ligaments (e.g., knee joint ligaments).
  • Muscle tone around joints (e.g., rotator cuff for shoulder stability).

Conclusion

• Stability vs mobility trade-off.
• Importance of understanding joint types for clinical anatomy.