last year, i had to read trauma X-rays at Pitt, UCLA, Wash U, and HSS. read a joint XR at rush, had to identify a vertebrea at Rush (know where the cord ends, orientation of facets for lumbar vs. thoracid and you should be fine) Harvard asked tons of questions about my research (a few questions about all 5 things I had on my CV) in the chairmen room. not hard questions, but definitely in a rapid fire method from one topic to another. as long as you really know your research, it was fine, just be prepared. almost all programs ask about research, but none as thoroughly as harvard.
i don't think you can really prepare for the x-rays as it varied from a pelvic fx (wash u) to humerus fx (pitt & hss) to ankle fx (ucla). just know the descriptive factors for any fx. i don't think they expect you to know classification systems (none asked me to classify the fx). although i was asked about open fx classification at hss (i.e. gustillo).