Hi, sorry for the late reply.

The following article on eMedicine, which is a good reference that I use, could be useful:
http://emedicine.medscape.com/article/1240 467-overview

Does it happen in both arms? (bilateral cases make up 60 % of the only 350 documented cases)

As per date, I don't think we are sure of the exact aetiology because the condition is so rare. It is a congenital anomaly, so perhaps mentioning the drug to the dr might give insight towards if you have it or not.

When you turn your arm from palm facing down to up, as in turning back pages of a book, does it cause pain or the cracking sensation?

Thanks for the response! In my case, the cracking only happens in my right arm. It's hard to explain how I crack it...I bring my hand up towards my ear (palm facing my head) and then stretch it to the right so my palm is facing up...that's when the cracking occurs. Sometimes it feels like it catches and it hurts. It doesn't happen when just turning my arm from palm down to palm up though. The fact that I can even do that motion makes me think I don't have any form of radioulnar synostosis, since that's one of the main things my brother can't do from his elbow. He has to do that motion from his shoulder.

But thank you for the information and the link! I will definitely have to look more into this.

Hi,

My 24 month old son has been diagnosed with radial ulnar synostosis. We have found that it can run in families. After my son was diagnosed we found out my husband's grandmother (deceased) also had it. After doing some additional research we found that if you have been diagnosed with this you should be screened for heart and kidney problems as they can occur at the same time in fetal development that causes something to go wrong with the arms. We had my son screened and he does have a congenital heart defect, bicuspid aortic valve. He was showing no symptoms or problems because of this. After that, we decided to have my husband checked as this is coming through his family. It turns out he also has a bicuspid aortic valve and a very slight irregularity in his radius, which we found through an x-ray screening. (nothing you would ever know about, except on x-ray). You might want to have an xray done to check for any irregularities. I think I do recall reading that some drugs taken in pregnancy can cause arm irregularities. I believe it was Thalidimyde, but can't really recall.
Liz

Oh wow! That's really interesting. Thank you for the response. I'll definitely have to talk to my mom some more and try to get the name of the medication out of her. And I may go get an x-ray just to be on the safe side.

Thanks again for the response...it was really helpful!

I am a 65 year old female with radial-ulnar synostosis both arms, the left worse than the right. I have functioned very well during my life but now have arthritis in shoulders and hands and upper back and neck. I have compensated by using my shoulders to turn my right hand over. I have not been able to turn my left hand over. I now am having joint replacement in my left thumb due to collapse of my basal joint, I also have dupretrens contracture both hands and have had repair done on that. I wish I had oc therapy when I was younger but didn't know what I had till just recently