Actually, the change fee is waived for medical. I just did the same with United. My dad went into the ER like 2 days prior to my flight date. I cancelled my trip immediately. (turned out not a serious problem, so I got to go on a different trip the following week).I just looked it up, and they waive the change / rebooking fee if the schedule change is more than 30 minutes (which it is). If it is more than 2 hours, you can request a refund (it's not). It's not clear about fare difference, though. I'm hoping if flights in March are more expensive, they won't charge me the difference. Will let you know what I find.
I haven't tried to use the credits yet. But I supplied the necessary information and was told that would qualify for waiving the change fee. Will know when I need to use it.
I presume the arm break was non-displaced? If so, I wouldn't ski. In fact, I would walk carefully for the next 6 weeks. A fall that displace the break would means surgery to pin it back to position. That's a big risk to take.