Crohn's Arthritis is not damaging to the actual joint. The reason for joint pain caused by Crohn's(other than chronic steroid use) is because inflammation from the gut circulates through your body and targets joints as it is circulating- Thus the feeling of joint pain.
Usually, not always, Crohn's arthritis means their is inflammation in the gut somewhere and for the joint pain to go away, the Crohn's flare needs to get taken care of first. I have Juvenile Rhuematoid Arthritis AND Crohn's. The Sulfasalazine does take a while to kick in. I've been flaring for a while & just started Sulfasalzine in April? It is a DMARD and an 'old drug' used for RA. Crohn's arthritis is more of a painful nuisance rather than a disabling disorder like osteoarthritis/RA/JRA. It's worth discussing with the GI about switching over to a Biologic. The biologics work great for Crohn's arthritis. I know a few people with Crohn's & their only symptom is joint pain. No gut pain, 'D', cramps etc. They have found joint pain relief & remission with Remicade. Some people never get relief from the bad joint pain. That's just Crohn's for ya. For my arthritis(not sure if it works for Crohn's arthristis)but I use a heating pad/blanket(depends on how many joints are hurting) and then rotate heating pad and ice packs. Icyhot is always good too. Exercise is good for relief. It may hurt and you may feel too tired but in the long run, it's for the best. My joints usually feel better after some stretching/jog.
Like previously mentioned, this is very common and probably the most common EIM of Crohn's. Other than Sulfasalazine & biologics, a Rhuematologist can't offer much help.
Take care!