P.K.
I'd be mad as well. I'd wait for a few days until you have your emotions on low, then I'd call, making sure that you don't use anger in your choice of words and talk directly to your doctor...not his assistant or voice-mail.
I'd start by saying, "I've still got some concerns about my son's back, and I was able to consult a chiropractor's view on my son's x-rays, which in her opinion, gave her the impression that my son may have scolosis."
Then, confirm with him or ask him to re-look at it to either verify or back-up his claim of "normal". Then, if he confirms the scolosis diagnsis, then...ask how the diagnosis and x-ray was mis-read. He needs to explain to you what happened and why he missed it. If he deny's the claim again, ask him for a referral to get a 2nd opinion.
Keep the diangosis of your chiropractor friend out of it. I'm pretty sure that in the medical field, Chiropractors and Doctors do not have a good bridge of working together so this could cause some stress in finding out the truth...simply because your doctor may not want to admit that a chiropractor dianosed his patient better than he did. If you ask him to re-look at the x-ray, perhaps once the problem has been laid out for him, he'll see it. Either way, he could be in hot water with you...and that is not your problem. You are the advocate for your son so be proud that you at least saught help from the chiropractor and are looking into this further.
Hopefully...your doctor will see nothing...because no one should suffer from scolosis. However, you'll be back to square one looking for a solution for your son's back pain. Sort of a double edge sword I guess. Like finding the lesser of two evils.
The hard thing about medicine is that us non-medical folk are stuck trusting our Doctors because we know nothing about medicine. People are mis-diagnosed everyday and it's really difficult persueing a malpractice case...not that you want to at this point, but...it's sort of fighting a losing battle. We all need to learn to be our own advocate for our health because even Doctors don't know everything. If in your case, your doctor did mis-dianose, you could start by filing your complaint with the Board of Directors at your Doctor's hospital. Hopefully it won't need to go that far.
Good luck.