The patella, the largest sesamoid bone in the body, is located in the tendon of the quadriceps femoris muscle. It protects the knee joint and increases the moment arm of the patellar tendon. The articular surface is situated on the proximal two-thirds of the underlying surface of the patella. The apex where the patellar tendon attaches is extraarticular part of the patella. The femoral condyles located at the distal part have the joint surfaces of patella. The trochlear notch divides these surfaces into two facets at the distal femur and utilizes intercondylar notch of the femur posteriorly. The entire articular surface of the patella is never in full contact with the femur at any time. In flexion of the knee, the articular surfaces in the proximal role of the patella, while in extension, the proximal of the patellar apex are in contact. During flexion, the patella descends vertically over a distance twice its length, about 8 cm. In complete flexion at 135°, patella is located in front of the interchondylar notch, contacting with the lateral joint facet and the residual medial joint facet. Both body weight and contraction of quadriceps femoris muscle lead to a pressure on the patellofemoral joint. High degree of reaction forces in the patellofemoral joint may be seen during activities in which knee flexion is higher, such as ascending and descending stairs.