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How does a bursa reduce friction around a moving joint?

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Medical illustration of a human knee joint in a parasagittal section just lateral to the midline, labeling ligaments, cartilage, meniscus, patella, synovial structures, and surrounding muscles and fat pads. — joint The ligaments and cartilage in a knee joint.

A bursa reduces friction around a moving joint by acting as a small, fluid-filled cushion or sac positioned between moving structures, such as tendons, muscles, ligaments, and bones.12

These sacs are typically lined with a synovial membrane that secretes synovial fluid. This transparent, viscous fluid serves as a lubricant, allowing the surrounding tissues to glide smoothly over one another during motion without excessive mechanical irritation or stress. By providing this cushioning effect, bursae protect the integrity of the tissues at points where they would otherwise experience significant friction against bony prominences.123