For my Oregon claim in 03 , after a denial, my atty wrote letters to billers so I could keep being treated, they more or less put the billing on hold , but I gave my med ins as a secondary payer.

If you weren't getting any tx for the arthritis previously, then it shouldn't be considered..
The injury set it off & aggravated it.

I don't know how different the WA rules are , but it seems like your atty should have some ways to get you treatment and have the bills on hold until the hearing..

Plus does your atty have any suggestions for the illegal firing?? You might get a lot more it that can be proven or changed to a layoff, or at least unemployment benefits.. or any FMLA benefits???
How many employes at that company?

My brother tore his meniscus while hiking and after 6 months eventually had surgery for it. But he didn't have any arthritis.

I would look around for wrongful firing information..on the WA state website first, rules might vary state to state...