It can be a little confusing when deciding the best test for knee osteoarthritis and degeneration. However, it's really quite simple - if the pain came on without trauma "atraumatically", then an erect radiogram is the best way to start. An erect AP, lateral , flexed AO and Patellofemoral view is the place to start, especially if the patient is middle aged or older. US or CT have no place, and MRI is really best for traumatic injuries on young patients.