While you’re having pain around your kneecap, eliminate elements that require the knee to do extra stabilizing work. Run on flat, even surfaces, stay off of tracks and twisting trails, and avoid downhills. Runner’s knee (patellofemoral pain syndrome to the medicos) is a good injury to finesse your way through on a treadmill. Putting the treadmill on a slight uphill grade should relieve some of the pressure on the knee.
Weak hips and glutes have been shown to be a key factor in developing running-related knee pain, because the knee tries to pick up some of the stabilizing work the muscles of your
midsection are supposed to be doing. Every runner should devote time to building stronger hips, but especially those with one or more episodes of knee pain.