my dogs back legs

Question
Hi,
My dog is an black lab and australian shepherd.  We adopted her when she was about 4 mo old and she is about 15 mo right now.  She was obviously abused in some way b/c she is very timid w/ new people and growls and barks w/ them.  She is scared of loud noises and is very skiddish.  She has improved but we have noticed that she gets up like an old lady as if she has arthritis.  She will not let me touch her back legs and i cannot trim her her back paws nails.  What could be wrong?  She is very sweet, but I fear she will bite someone, b/c of her shyness and her back legs.  Could it be arthritis already or possible hip dysplasia.  
Thanks,
Beth

Answer
Hello Beth,  I think you are on the right track, take her to the vet for x-rays, this will answer your questions of arthritis or hip dysplasia.  There is however also the chance she might have lyme disease.  This disease affects the joints and her symtons are very similar to lyme disease.  A trip to the vet will get you the correct answer.  Good luck, she is lucky to have been adopted by such a concerned owner.  Thanks for asking, Cindy Lou :)