If your doctor told you to lay off any exercise to let your tibia heal, you're going to have to listen. you will NOT derail any of your efforts at good health or weight loss because you can't exercise. the fact is, when it comes to losing weight or even gaining it, what matters most is what we eat. Good nutrition is what takes the weight off and keeps it off. Exercise is what keeps our bodies fit and healthy. In short, you can't outrun a bad diet with exercise.
So, as long as you eat right and watch your portions you will not gain any weight while your leg heals. Take this time to really pay closer attention to your diet. And don't drastically cut your calories either. Your body needs those calories to MEND your fracture.
See, that's another problem. When you cut calories and continue to exercise, your body doesn't have enough energy to repair itself. Thus the reason to eat as healthfully as possible. Try to eat at maintenance level calories. Don't starve your body of the calories it needs to be healthy.
As far as exercise, the jumping has to stop. If your doctor gave you the okay to walk, stick to walking. And if you really want to do something intense, sit in a chair and do some upper body strength exercises. Use resistance bands or hand weights. Using heavy enough weights will get your HR up.
But once again, increasing your heart rate is not what helps a person lose weight. Watching what they eat is what does.