Stop in for a cup of coffee

Well based on my experience the letter always reads that way. You go to a medical review based on the Dr's comments.
A medical review board then determines if you go on to a discharge board.
I'd guess you wouldn't face discharge with a pending surgery for your knee.
I served more than 10 years with a 50% hearing loss and tinnitus. They do give waivers.
Don't get discouraged, its a process, its the Army.