I have osteoarthritis in one knee, and I've been to several rheumatologists and orthopedists. When they find out that I have Crohn's, they all reiterate that I must never take aspirin or Ibuprofen, because both drugs have been documented as causing additional damage to the digestive tract of people with CD. When I've asked them what I can use to treat arthritis pain, they basically tell me that I'm totally out of luck--I can use Tylenol for the pain, but I can't take anything that will deal with the inflammation.
When my arthritis acts up, I tough it out--or give up and take a hydrocodone for relief.