The important parts of the knee include bones, ligaments, tendons, and cartilage. The Femur is the large bone of the thigh. The Tibia is the large bone of the lower leg. The Fibula is the small bone of the lower leg. Two ligaments are found on either side of the knee joint - the Medial (inside) Collateral Ligament and the Lateral (outside) Collateral Ligament.

Inside the knee joint, two ligaments stretch between the femur and the tibia. The Posterior Cruciate Ligament lies behind the Anterior Cruciate Ligament. The difference between ligaments and bones is that ligaments connect bones together, while tendons connect muscles to bone. Two structures called Menisci sit between the femur and the tibia. These structures are sometimes referred to as the cartilages of the knee.

Articular Cartilage is the material that covers the ends of the bones of any joint. This white, shiny material has a rubbery consistency. The function of articular cartilage is to absorb shock and provide an extremely smooth bearing surface to facilitate motion. There is articular cartilage essentially everywhere that two bony surfaces articulate. In the knee, articular cartilage covers the ends of the femur, the top of the tibia and the back of the patella.

Finally, the Extensor Mechanism sits in front of the knee joint. The Patella is the fourth bone of the knee joint. The Patellar Tendon connects the patella to the tibia. This tendon covers the patella and continues up the thigh as the Quadriceps Tendon.