Treadmill Vs. Stationery Bike: A Fat Burner's Query

Hey all,

Wanted to ask a simple question.

I have been on a steady exercise program for the last 7 months or so that involved me simply walking outside with weight training at home. I recently began using my university's gym and went straight for the treadmill. I began using a preset workout that incorporated incline. Now, according to the machine in about 45 mins I'll burn between 300-400 calories in a workout. This is all fine and dandy but I do not feel like I am getting the full potential out of what the treadmill has to offer because of some physical limitations on my end.I was hit by a car about 2 years ago and because of the leg injury I cannot go past 4.7 speed on the treadmill without my knee giving out or simply losing my balance. I read somewhere that a stationary bike can get more done for someone in my position because of the lack of impact on the knee. Have you guys experienced any truth to this?

The goal here is to burn fat. Though I am getting a decent workout on the treadmill I feel that I am not pushing myself as far as I can be. Could the change to the bike potentially heighten my rate of fat burning?

TL;DR Treadmill or Bike, What burns more fat.

Edit: Couldn't fix the spelling for "Stationary" in the title but did in the paragraph.