From another perspective -
You have a disability.
Albeit a short term one, but a disability nonetheless.
You didn't say where your employer is, but if it's in any of the English speaking countries, then it's very likely there is some kind kind of employment law in place to protect you from any kind of discrimination based on your disability. That means your employer cannot treat you any differently (in a negative way, at least) than any other employee. In fact, they may even be required to provide certain additional accommodations specifically for disabled employees. An injury requiring crutches probably won't limit your mobility all that much so it's unlikely they'd really need to change anything to accommodate this specific ailment, but still, they will be aware of this possibility and may have already added automatic doors, elevators, ramps, etc. for other disabled employees, and so you'd at least benefit from those improvements.
To be honest, when they see you come in on crutches, your employer is probably going to be more nervous about themselves making a good impression on you than the other way around. After all, they now have all the aforementioned additional responsibilities to live up to, at least until you get better.
All that said, I would not expect anyone to think you're making a bad impression anyway. As others have said - accidents happen. It may even be a nice little icebreaker, giving you something to start a conversation over with your new team mates, as long as you're comfortable chatting about whatever happened.