Anatomy means the 'shape' of the structures in the body, and how the different parts correspond to one another.
Three separate articulations
The anatomy of the knee seems quite simple, but the 'functional anatomy', ie how the pieces operate together, is quite complex. The knee joint is really three separate joints - two 'tibio-femoral' joints (contact surfaces of tibia and femur), and one 'patellofemoral' joint (contact surface of patella and femur). The thinner fibula bone at the side of the tibia does not form part of the knee joint itself.