Repetive injury. Some people do, of course some don't but you are more likely if you are doing the same repetitive activity daily without a rest period. Also changing the workout routine is important. Running is a high stress and overweight people and those with either knock knees or bowlegs also may develop knee pain.
Possibly. All exercise provides wear and tear on your joints. Treadmill would be less damaging that running on hard pavement. You can also minimize the damage by taking glucosamine supplements; eating a well balanced diet and adequate hydration as well as treating any inflammation rapidly. I would suggest cats claw for this and definitely protandim. Check www.Medacpc.Com for info on this.