The knee is the largest joint in the body. A healthy knee moves easily, allowing you to walk, turn, and squat without pain. A complex network of bones, cartilage, ligaments, muscles, and tendons work together to make a knee flexible.
Your knee joint is made up of three bones. Your thigh bone (femur) sits on top of your shin bone (tibia). When you bend or straighten your knee, the rounded end of your thigh bone rolls and glides across the relatively flat upper surface of your shin bone. The third bone is often called the kneecap (patella), which is attached to the muscles that allow you to straighten your knee. Your kneecap provides leverage that reduces strain on these muscles.
Ligaments (another type of soft tissue) lie along the sides and back of the knee, holding the bones of the knee joint in place. These ligaments work with the muscles that control the bones, and the tendons that connect the muscles to the bones, so you can bend and straighten your knee. Fluid-filled sacs (bursae) cushion the area where skin or tendons glide across bone. The knee also has a lining (synovium) that secretes a clear liquid called synovial fluid. This fluid lubricates the joint, further reducing friction and making movement easier.
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