Also known as "runner’s knee," patellofemoral pain syndrome is knee pain and swelling caused by stress put on the knees by runners and other athletes. It involves a dull pain under the kneecap where it connects with the thigh that is worse with flexion and use for running.

Patellofemoral pain syndrome is often caused by improper conditioning and running in shoes that do not fit properly. Runner’s knee can be treated using the RICE (Rest, Ice, Compression, Elevation) formula initially, and with physical therapy once acute symptoms have subsided. Surgery may be needed in some serious cases.