Lecture Notes on Synovial Joints and Osteoarthritis

Introduction

• Teaching by video can be challenging despite experience.
• Today's focus: Synovial joints, specifically the knee joint.

Overview of Synovial Joints

• Definition: Joints allowing a wide range of movement.
• Importance of structure for mobility and stability.

Key Structures of Synovial Joints

1. Articular Cartilage

   • Covers the articulating surfaces of bones.
   • Composed mainly of type II collagen, with type IX and XI collagens.
   • Contains proteoglycans, particularly aggrecan, which hold water.
   • Provides low friction and withstands compressive loads.
   • Chondrocytes maintain the extracellular matrix, responding to loading.
   • No nerves or blood vessels present; nutrients diffuse through synovial fluid.

2. Synovial Capsule

   • Surrounds the joint, consisting of two layers:
     • Outer Fibrous Layer: Tough, continuous with the periosteum.
     • Inner Serous Layer: Responsible for creating synovial fluid.
   • Provides stability and contains synovial fluid, which lubricates the joint.

3. Synovial Fluid

   • Acts as a lubricant, allowing smooth movement.
   • Carries nutrients and removes waste from articular cartilage.
   • Non-Newtonian fluid: its properties change with load.

Functionality and Mechanics

• Synovial joints must balance mobility with stability.
• Example: Knee joint is a hinge joint with limited rotation, surrounded by ligaments and muscles for support.
• Menisci: Fibrocartilaginous structures that stabilize joints and distribute load.

Osteoarthritis

• Definition: Degenerative disease affecting articular cartilage.
• Causes: Imbalance in degradation and repair of cartilage, hereditary factors, injury, and abnormal loading patterns.
• Common misconceptions: Running does not wear out cartilage; rather, improper loading does.
• Current recommendations: Maintain joint use to prolong cartilage health, manage pain, and keep active.
• Treatments: Joint replacement may be necessary in severe cases.

Conclusion

• The structure of the synovial joint includes articular cartilage, synovial capsule, and synovial fluid for effective movement.
• Understanding osteoarthritis is crucial for managing joint health and activity levels.