I broke my arm.
In my language (Persian), if I say this to one of my friends, her response would be like this: “Are you out of your mind? Why did you break your arm?” because it implies that I broke my arm on purpose. And we usually say this in passive voice.
So I actually think passive is more correct. I mean, you fell down and your arm was broken. You didn't want to break your arm. So I don't get why we say this in the active voice.