The old adage that running will ruin your knees has long been debunked. (If you need another example, here's one from last year.) However, if you already have a 'bum' knee that's suffering from osteoarthritis, should running be avoided? A new study in the journal of Clinical Rheumatology, led by Grace Low, tested 5,000 Americans. Within that group, 1,203 of them had OA (osteoarthritis) in at least one knee. Of that group, 138 were runners. (And yes, I know this isn't a big