A joint is the connection between two bones. Joints and their surrounding structures allow you to bend your elbows and knees, wiggle your hips, bend your back, turn your head, and wave your fingers to say bye-bye.
Smooth tissue called cartilage and synovium and a lubricant called synovial fluid cushion the joints so bones do not rub together. But increasing age, injury,or carrying too much weight can wear and tear your cartilage. This can lead to a reaction that can damage your joints and lead to arthritis.