The patella (also known as the kneecap, Latin: patella) is a flat triangular movable bone at the front of the knee joint. The patella is embedded in the quadriceps tendon.

The patella is a sesamoid bone, the largest one in the human body. It is roughly triangular-shaped and has three main parts:

    • base of the patella,
    • apex of the patella, and
    • articular surface of the patella.

The base of the patella is the broad, superior border of the bone. The tendon of the quadriceps femoris muscle attaches to the base of the patella, with the vastus intermedius attaching to the base itself, while the vastus lateralis and vastus medialis attach to the outer and medial borders of the patella, respectively.

The apex of the patella is the pointed and most inferior portion of the bone, and it gives attachment to the patellar ligament.

The articular surface is the cartilage-covered posterior upper part of the patella that faces the femur, articulating with the patellar surface of the femur. Because of the significant stress on the patellofemoral joint during resisted knee flexion, the articular cartilage covering the patella is among the thickest in the human body.