I was watching the Biggest Loser recently, and there was a guy on there who tore his ACL, but stayed on the show for quite a bit. He was still losing lbs weekly, and he wasn't even able to hardly! There are some machines at the gym, or even exercises you can do at home that can still get you moving a bit. I would google wheelchair exercises or something similar. It may have some good stretching and exercising tips that can keep you going.
I am a full believer though that the main culprit in weight gain is what you are eating. 28 Lbs (or 13 kg) is a lot to gain in 7 months. There had to be more to it than just being off your feet. Just remember, that taking it off is way harder than it was to put it on! (oh how I wish it was the other way around).
Also, if you are restricting calories, make sure you are restricting the right amount. Serving sizes are always "based on a 2000 calorie diet" but I've recently found that very few people should be on that high of a calorie allowance, and thats only to maintain. Never to lose. There is a calculator online somewhere that you put in your age, weight, height, and amount of exercise you do, and it gives you how many calories you should eat to maintain or lose. For me, I am 183 lbs and 5'5" and with moderate activity, it suggests I eat no more than 1,500 calories a day to lose weight. That is with moderate exercise. I changed the setting to "sedentary lifestyle" and it said no more than 1,100 calories. That's a big jump. So maybe just make sure that you are eating enough to lose, not just maintain.