
Have you been in touch with pups breeder? If they are experienced and knowledgable in the breed they should be a great source of info for you.
My Mastiff develpoed a limp and at 6 months old, xrays confirmed he had elbow displasia, he also had his hips xrayed at the same time because both myself and the vet were concered with his movement - it seemed too 'loose' but on waking seemed stiff and he looked like he lacked strength in the back legs and had intermittant limp in them. The vet said the hip-xrays showed his hips were not very good. He also had problems with his pasterns which the vet said would need opperating on.
I got in touch with the breeder who explained that it's very common in this breed to go through some very akward growth stages etc..he also told me be about a 'corrective diet' (as I had deviated from what I was frst told :( ) and not to worry he would be fine, he also advised against any operation for the ED until the pup was at least 12 months old.
In the mean-time, the vet had sent the x-rays to a specialist who said the hips were fine!!! The specialist aslo confirmed the pasterns would need operationg on.
Now the dog is 15months old, his back end is great and he is walking fantsatically and there is no problem with his pasterns (& not had the Ed opperated on), everything the breeder said was spot on :)
Large and giant breeds can go through some very odd growth stages that some vets will not recognise. Please get in touch with pups breeder before you consider an opperation, 5 months seems so very young, they should be able to offer advice on what route to go down, if any.
Oh, just to add, when my pups ED was first diagnosed he could barely walk (hence the vet saying it needed opperating on ASAP), after sticking to the breeders advice you wouldn't even know there was a problem with him :)