daybyday, so sorry to hear that. I've been plagued by knee issues for what seems like all my life! I've been skiing since I was 3 and used to be on a racing team, also used to play basketball and volleyball (those dives will kill ya) so yeah I've pretty much distroyed my knees. Even had an ACL reconstruction when I ripped it in half, apparently your leg isn't ment to turn completely around, haha.
But anyway, back to the point, don't let your knees get you down! Talk to your physio about different options/ideas for continuing your weight loss. They may suggest water therapy, which is great for your knee and has good overall health benefts. I'm sure they'll start you on a strength training routine, the best thing to do is ask questions and explain your goals/situation, they're there to help. You can then build up a good routine once your knee(s) get stronger and before you know it you'll be back to your ole running self! Believe me, once you regain a limb you have such a better appreciation for it. I never realized how much I enjoy just walking!
Good luck! Hope all goes well!