It is hard to say what the averages are for uro from year to year and the AUA does not publish such data. Specialty specific interview spreadsheets made on Reddit for Uro suggest it is around a 245, though it is all submitted by applicants. In reality you should be fine with a 240+ for most programs except the top 20. I know of some such top programs that screen out applications below a 250 and others screen at 245. I would say that your score of a 251 will not screen you out in that category from any program to be invited for an interview.
251 will not get you screened out anywhere. Now it's all the other stuff (letters, research, grades, etc.) that will determine where you get interviews