Basically, not much.
He did some tests (physical stuff to check Cavan's reflexes) and came to the same conclusion that the pediatrician did: brachial plexus palsy.
He doesn't know the extent of the damage. He said there's no way to know without an MRI, which is risky, since Cavan would have to be put to sleep for it. If the nerve is severed (which isn't likely since he has minimal movement) there's no hope that it will recover. If the outside of the nerve was stretched (leaving the fibers inside intact) it will likely recover.
He also doesn't know whether or not he will recover, or to what extent. He is optimistic, since the baby seems to show minimal improvement since he was born. I realized that I had the video camera with me, and that Hubs had taken video of his first bath at the hospital, so the neurologist and I watched it together. It looks like Cavan is moving his arm slightly more now than he was two weeks ago. Slightly. As in, I can't really tell that much difference.
Basically, we have to just be patient, wait, and continue to pray. The doctor said that if Cavan's nerves heal, and he regains use of his muscles, it will happen within the next six months. Beyond that time period, there usually isn't any progress.
He also said he doesn't think Cavan is in pain from this. I think that's bunk. It's only when you move his arm (not every time, and not in every position) that he starts screaming and can't catch his breath. It's a completely different cry from his "I'm hungry," "I'm wet," "I'm bored," "I'm sleepy" cries.
I left the office frustrated. I wanted answers, and there weren't any. We don't know any more today than we did last week.
He either wants to see the baby in a month, or have another neurologist see him, to check his improvement. I think I'm going to try to get an appointment with another doctor, just to see what they think.
Please keep praying for Cavan. It looks like (unless God gives him a miracle) that we won't know for sure for another six months.