Would a dislocated knee show on x-ray?

Yes: Usually a dislocated patella will spontaneously reduce with knee extension.

Sometimes.: If you dislocate your patella and it remains dislocated, then you will see it on X-Ray. Similar findings are seen at other joints in the knee, possibly with fractures. However, in adults more than 50% of the dislocations are NOT seen on X-Ray because these joints tend to spontaneously reduce after the injury. In these cases, a dislocation with possible fracture is best seen with MRI or CT study.