Yes, it could be an extra-intestinal complication of having an UC. In fact, it is the top complaint for us, about
25-30% of us get joint pains. It's known as an arthritis (meaning an inflammation of the joints), and can happen to us at any age. It mostly effects the large joints in the hip, based of spine, legs, and arms. Here's a good read on it from the CCFA:
https://www.crohnscolitisfoundation.org/sites/default/files/legacy/assets/pdfs/arthritiscomplications.pdf