The knee joint is the largest joint in the body, It is made up of the lower end of femur (the thigh bone), and the upper end of tibia (the shin bone). The femoral condyles (lower rounded end) usually glides smoothly on the tibial plateau (flat upper surface) allowing for smooth, painless motion of the lower limb. The knee joint is a hinge joint. The third bone is often called the kneecap (patella), which is attached to the muscles that allow you to straighten your knee. This bone provides leverage that reduces strain on these muscles.
A complex network of bones, cartilage, ligaments, muscles, and tendons work together to make a knee function normally.The quality of smoothness where each bone moves upon the other becomes important in the function of the knee joint. The surfaces of all three bones coming into contact with each other are normally covered with a smooth gliding surface known as articular cartilage, This cartilage cushions the bones and enables them to move easily.Disease or injury can disrupt this resulting in pain, muscle weakness, and restriction of mobility at the knee. The surfaces in knee joint are covered by a thin, smooth tissue liner called the synovial membrane. This membrane releases a special fluid that lubricates the knee which reduces friction thus making movement easier in a healthy joint.