...i run (casually) with my girlfriend sometimes...excuse the wardrobe malfunction in the pic below
(it's a Picasso)...but i prefer a fast walk because it's less stress on my body.
...btw martian...my girlfriend had surgery on her knee...Arthroscopy...NOT knee-replacement. The surgeon goes in and cleans out the arthritis...and she's as good as new now. It took 3 months of therapy before she was running again...and not really back to normal for a year...but now all is perfect...but i highly recommend that surgery for you...choice of doctor is critical.
...Picasso