Synovial fluid is a clear, viscous (thick and slippery) flui
Synovial fluid is a clear, viscous (thick and slippery) fluid found inside synovial joints, such as the knee, shoulder, hip, elbow, and ankle. It is produced mainly by the synovial membrane that lines the joint capsule.
Functions of synovial fluid
* Lubrication: Reduces friction between the articular cartilage during movement.
* Shock absorption: Cushions the joint and distributes forces during weight-bearing activities.
* Nutrition: Supplies oxygen and nutrients to the articular cartilage, which has no direct blood supply.
* Waste removal: Removes metabolic waste products from cartilage.
* Protection: Contains immune cells and proteins that help defend the joint against infection.
Composition
Synovial fluid consists of:
* Hyaluronic acid – gives the fluid its thick, slippery consistency.
* Lubricin – further reduces friction.
* Water
* Electrolytes
* Glucose
* Proteins (small amounts)
* White blood cells (normally very few)
Normal characteristics
* Color: Clear to pale yellow
* Appearance: Transparent
* Consistency: Viscous (“stringy”)
* Volume: About 0.5–4 mL in a normal knee joint
Clinical significance
Analysis of synovial fluid helps diagnose joint disorders:
* Infection (septic arthritis): Cloudy fluid with a very high white blood cell count and bacteria.
* Gout: Presence of needle-shaped monosodium urate crystals.
* Pseudogout: Presence of rhomboid-shaped calcium pyrophosphate crystals.
* Osteoarthritis: Usually clear fluid with a mild increase in cells.
* Rheumatoid arthritis: Cloudy fluid with increased inflammatory cells.
In summary, synovial fluid is essential for smooth joint movement, cartilage nutrition, shock absorption, and joint health.
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