[gemy]

Leggs Perthes can start to evidence itself about 7mths or sometimes earlier if it is particularly bad.
I would be going to a board certified orthopaedic vet. They won't recommend surgery if surgery is not required. Also their Xray techs tend to be better, and your dog may not need to be sedated for this Xray.

If the knee is good, then holding leg up, logically can come from two different places, look upwards towards the hip, and below knee to "ankle" and all the toe digits. Something is obviously bothering your pup, given the leg up position.

I had Razzle's OFA's on hips done, and no sedation was necessary.