Final answer:
The knee joint is formed by the articulation of the femur (thighbone) with the tibia (shinbone), and the femoropatellar joint with the patella (kneecap), making the Femur and tibia the correct answer.
Step-by-step explanation:
The anatomic structures that articulate to form the knee joint include the femur and tibia, which create the medial and lateral tibiofemoral joints, and the patella, which forms the femoropatellar joint with the distal femur. The femur, or thighbone, is the longest and strongest bone in the body, articulating with the hip bone at the hip joint on its proximal end and with the tibia at the knee joint on its distal end. The patella, or kneecap, improves knee extension by reducing friction as a sesamoid bone embedded in the quadriceps tendon. The tibia, or shinbone, directly below the knee, articulates with the femur and serves as an essential weight-transmitting structure from the femur to the foot.
The correct answer to the question, "What anatomic structures articulate to form the knee joint?" is therefore option (a): Femur and tibia.