It certainly is but surprisingly, it is not much more prevalent than in the general population.  This is largely because runners are typically more fit than the average person, maintain a healthier body weight than the average person, and have generally very good lower limb muscular strength.  Runners suffer knee pain and injury from different causes, most commonly repetitive strain.  Running is very much a front-to-back based activity, meaning that certain muscles including your quadricep and hamstring, become disproportionately strong.  If a runner does not take care to cross train and work specifically on lateral strengthening for both groin and lateral pelvic muscles, their risk of suffering knee pain and injury increases.