How are your other CD symptoms? You could be headed into a flare. My joints always get worse prior to a flare. You are correct about
arthritis showing up after the CD diagnosis in some patients. I would go ahead and ask for a Rheumy referral. Some patients have trouble with the joints actually fusing together and anything preventative you can do certainly would be worth it's weight. If it turns out to be nothing but regular old CD joint pain then at least you'll be established with a Rheumy should you need him/her in the future. You could also use the google search at the top of this page for "Crohns and Spinal Arthritis" for more detailed info.
Good Luck and let us know what happens.