I know how you feel as I am in the same boat as you -- I fractured my left calf bone some years ago and it never really healed properly (had a blood clot in it etc); and it still swells up to this day esp as the day goes on. I also damaged my right knee severely (kept dislocating); but it is much better than before. If I over=strain it by walking or standing on it too much or for too long, it collapses on me.
I would read about all these people doing running or jogging to help them in their WL and saw how much it was helping; but like you, I can't -- too many injuries there. SOOOO, I did some research and found some other alternatives ~ the one you might like to try most is called POWER WALKING (used to be called Speed-walking and is an Olympic event even). You start off walking normal but pumping your arms; then as you go along, you speed up the pace. You go back and forth; faster, slower, faster, slower, etc. You burn more calories this way too; similar to running.
The other one that I can do right now is -- NORDIC or SKI-WALKING; you can do this winter and summer. Some people call it TREKKING or hiking too; so take your pick. You buy a pair of ski poles or trekking poles. Trekking poles have 3 different pairs of pick ends; one for snow, hiking, and walking, I think. I picked up two pairs of almost new poles at our local second-hand thrift shop for only $2.00 a pair. I love them.
They give you a full body workout becuz your arms are going as you walk; and the poles help you to walk FASTER too. That helps you to burn more energy as well. The first few times, my shoulders were sore, but that was becuz they weren't used to it; later on, that goes away. I use them a lot now (as well as my two canes) for walking anywhere; especially on uneven ground or surfaces.
You can get a nice MP3 or IPOD or tape recorder and listen to bouncy music as you go, that can help you pick up the pace a bit. I bet you could do this instead; if I can, anybody can.