Well that sucks. I've cycled with a leg half-cast and have had a full arm cast but never just a forearm cast, so can't say I have hiked with one.

First challenge will be putting the pack on and off. Trekking poles would be dubious, although one will be fine. Various camp chores will be harder and the whole bathroom routine will be...interesting. But as long as you're not in pain you'll adjust and adapt.

Happy hiking,
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--Rick