What might this knee problem be?

Hello, my dad says his knee hurts, it's a dull throbbing pain and he seems to make it worse by doing things like climbing ladders, etc. It's only in one knee, he also has gout and is 6 foot and 300 lbs., I'm trying to get him out walking to lose weight but he says his knee is pretty bad.....is this arthritis maybe? Just wondering since his hands are okay and it's only in one knee......thank you