Mamby,
I saw you posted this 8 years ago. My daughter is 27 month old an she has the same problem. I took a video on youtube to show you her arm movements. If this is like what your son was doing PLEASE tell me what the problem was an/or how it has progressed and how you treated it.
THANKS SO MUCH i hope you get this email.
please watch the video below. it could be so helpfull
http://www.youtube.com/watch?v=pzEUTuJ_0_Q
you can call me on my cell if you want... its 314-803-4115 my name is Gus