Hi, Allan. I'm sorry to hear about the pain and worry you must be undergoing.

One part of me wants to tell you simply to rest and not play any instrument. Another part recognizes how much you want to keep playing.

Do you know anybody who has a mountain/lap/fretted dulcimer you might try? They are easy to learn, and maybe playing one will not hurt your arms. You can put it on your lap and simply drop your arms down to it. Or you can put it on a table (as I do) and let the weight of your arm press the strings.

I like the DAA tuning because of its simple fingering.