Over the last year, my left knee gradually started creaking as I walked up stairs, and became mildly uncomfortable during jogging and indoor rock-climbing sessions. After a few visits to my family doctor, a CT scan and some reading on the web, it's become clear that I have "runner's knee".
Runner's Knee occurs when the soft tissues under the kneecap become irritated, which usually happens because the kneecap doesn't track properly as the knee bends. The kneecap should move up and down smoothly in the groove between the two ball-like protrusions at the bottom of the upper leg bone.
As described here, the kneecap often fails to track properly is usually because one's foot pronates too much as one walks or runs.
Non-steroidal anti-inflammatory drugs like ibuprofen prevent soft-tissue regeneration, so should not be taken.
A period of rest from one's regular exercise regime is necessary. At least a couple of months.
Supportive, stable footwear is likely the most important single element in improving joint mechanics. No high heels or loose shoes.
Strengthening exercises such as squats (very light or no extra weight).
Glucosamine, Chondroitin and MSM may improve the rate at which the joint tissues heal.
I wouldn't be surprised if walking on cobblestones was good too, even though the study concentrates on the blood pressure benefits.