Some programs apparently don't even have their interns take the test.
Its worth remembering though that the AAOS puts out the OITE and often cites OKU in their answer references - so that is not a bad place to start if you are just focusing on the exam. As a former/life-long Hoya, I am partial to the 2 books put out from there:
Essentials of Orthopaedic Surgery (Paperback)
by Sam W. Wiesel (Author), John N. Delahay (Author)
-Short enough to read during intern year, more guided toward med studs though.
Principles of Orthopaedic Medicine and Surgery (Hardcover)
by Sam W. Wiesel (Author), John N. Delahay (Author)
-A bit bigger, more information but probably manageable during intern year.
But again, I have a huge bias - I wouldn't be in ortho if it weren't for the people there.
If you have little time (very likely) the most bang for you buck for the in-training is doing old questions and if you are repeatedly getting stuck on certain topics try to find a JAAOS article (again put out by AAOS) on the topic for an overview.
Just my 2 cents, good luck.