Years ago, we had a samoyed. When she was a pup I knew something was wrong with her back end. The vet said no she was fine.
We lived in the Yukon and the only vet did not have any equipment. I insisted on an X ray. So we had to wait for an X ray machine to come in. When it arrived she had an X ray and it turned out that she did have hip displaysia (sp??)
The vet told my husband that he was surprised that this was so. (He was new out of school and we were so glad to have a vet) She lived to 13 years of age.
No operations available at that time.
The moral of the story is, if your dog is yelping when you touch an area, there is something wrong. The only way to find out what it is, is thru the vet.
Good luck and please let us know how you make out.