I've rarely talked to a runner who has not had a knee problem at some point in their running background. The following excerpt from "Healthy Runner's Handbook" does a terrific job of explaining some of the sources.

"The knee is the largest and most complex joint in the body. Given the enormous stresses to which it is subjected during running, it is natural that knee injuries are common among runners. The potentially debilitating consequences of a knee injury reinforce the need for a focus on prevention.

Knee overuse injuries include patellofemoral pain syndrome (kneecap pain), meniscus wear and tear, tendinitis conditions both above and below the kneecap, bursitis, and loose bodies in the knee.

Overuse knee injuries are usually caused by excessive running, but