Are you on any medication for the arthritis/inflammation from the UC, anti-inflammatories, immunosuppressants etc...? Maybe for the UC itself?
Is there any way they can brace it? I've been referred to orthotics as my feet are a bit problem at the moment with RA, my ankles too but my feet are worse. Maybe something similar could help support wise?
Are you under rheumatology or orthopaedics (maybe the orthopaedic surgeon who did the arthroscopy) that you can get an appointment back with them or assess it or would you need a GP referral back.