What does it mean if my son has been recently diagnosed with radialulnar synostosis.?

Can be congenital or: acquired. It means there are abnormal connections between the radius and ulna, bones of the forearm, and as a result it is difficult to accomplish rotational movements of the forearm. It can result from trauma and in that situation may be able to be surgically corrected. http://rarediseases.info.nih.gov/gard/10876/congenital-radio-ulnar-synostosis/resources/1http://emedicine.medscape.com/article/124