Hi9 | What is Knee Replacement Surgery | మోకాలి మార్పిడి అంటే ఏమిటి - The Human being the knee joint is built between the two bones like thigh bone and leg bone that is Femur and Tibia when ever the joint is form there is a very smooth cartilage here, which is like a wet coconut. This is nourished by synovial fluid but as you grow older and as you become fat the cartilage becomes rough and the wetness of the cartilage goes down.