Patellofemoral pain syndrome (PFPS) is a condition that causes aching pain and irritation throughout the knee. Also referred to as runner's knee, PFPS usually affects the young, athletic, and the constantly active.PFPS is usually caused by overuse. Activities that involve running, jumping, and squatting put intense pressure on the knee, which can eventually cause damage. Other causes of PFPS include direct injuries to the knee, abruptly changes in the frequency of exercise, and misalignment of the knee joint. Those affected by patellofemoral pain syndrome, usually experience feelings of dull or aching pain in the knee. This pain will become worse when taking part in physical activities that require the knee to bend. This includes walking up and down stairs, sitting, or kneeling for extended periods of time, and going up or down hills.