Your best bet is probably to access (and probably pay for, sorry) articles from the American College of Veterinary Surgeons or the European College of Veterinary Surgeons. If your university has a veterinary school (or you have access to one), you may have free access to these journals. These will likely be the best sources of published articles on hip dysplasia. As far as assessing the radiographs, you can contact either the American or European College of Veterinary Radiologists. I haven't had to do these kind of radiographs in a while, but back when I did there are at least 2 different grading systems for hip dysplasia (at least early grading), so that may also complicate things. Hopefully these two sets of specialists can help you make sense of everything.

Ok thank you i will then try to have access to these two journals through my university. Thank you for the help :)

send me your email ....I will send you some articles regarding hip dysplasia;

look also to http://info.antechimagingservices.com/pennhip/

You should peruse the Orthopedic Foundation for Animals (OFA) website regarding this topic. They have a HUGE database on numerous breeds and will give you a good background on the German Shepherd Dog as they were one of the first breeds studied by OFA due to their use as working dogs. Additionally, if you haven't read it yet you should see if your university library has the textbook by Thrall called Textbook of Veterinary Diagnostic Radiology or our imaging journal Veterinary Radiology and Ultrasound, which are the primary literature for both the American and European diagnostic imaging specialty colleges. Thrall has a brief discussion on both PennHip and OFA style pelvis radiographs as well as the Roentgen findings correlated to hip dysplasia in dogs. 

I performed my MSc evaluating clinical signals of hip dysplastic dogs according with hip dysplasia degree. It is one of my publications. best regards

http://www.ncbi.nlm.nih.gov/pubmed/25394914