Joint pain and inflammation is not uncommon with UC. Fibromyalgia or chronic fatigue are also often related. Osteoporsis can be caused (or at least sped up) by steroids prescribed for UC.
I've experienced inflammation of the lower spine in relation to a UC flare. I've also noticed joint pain, stiffness and popping off and on. Mine seems to get worse if I consume dairy.
Have you tried supplementing with Omega-3? It's excellent for reducing inflammation in the colon and in the joints.
Diagnosed with ulcerative colitis spring 1999.
Maintenance dose sulfasalazine.
Probiotics, l-glutamine and fish oil caps. George's aloe vera juice. Oregano oil antibiotic, antiviral, antifungal. Long-term remission with only minor blips.