Not sure if this is comparable, but I fell HARD and shattered my patella this past December and I'm still recovering. Even though my body type is classic ectomorph, I assumed that the inactivity combined with the time of year (Christmas cooking & cold weather) would lead to weight gain. Instead, my weight stayed steady and I actually put on a little more muscle up top and my fat % dropped thanks to being on crutches for months.
Between the pain and the meds, my appetite just wasn't there. A friend of mine runs an Italian restaurant and he said he's noticed regular patrons who've had ankle and knee injuries don't eat as much as they had been and they all claimed to be losing weight. Perhaps the body is trying to protect itself from further injury and stress caused by increased load and pressure on the joint? Hard to say, but stranger things happen.
If you find yourself in a brace/cast, though, you will certainly lose muscle in that limb since it takes almost no time for an immobile muscle to forget how to function and start to atrophy. Recovery will be slow, but you're fortunate to have warmer temps on your side so no excuse for not getting out on your crutches for as much cardio as your body can handle.
Oh, and I'm sure they told you this, but DO NOT SMOKE! It seriously slows bone recovery (and you know how horrible it is for your body on a good day). Try to keep as much protein-rich food around as possible for the cravings. Maybe an easy to prepare, cold protein shake could be your new addiction.