The knee joint is formed by three bones: the femur, the tibia and the patella. the knee joint is the largest synovial joint and provides the flexion and extension movements of the leg as well as relative medial and lateral rotations while in relative flexion.
The knee joint articulations are two condylar joints between the femur and the tibia as well as a joint between the patella and the femur. Although the fibula is closely related to the knee joint but it doesn't share in articulation.
The knee joint is also formed by some ligaments and cartilage called (menisci) which are best imaged by MRI.
This 3D model was created from the file STS_045. The source scan be be found here.