I hope your husband has gotten some relief. I have had severe headaches for 1 1/2 years after retro surgery and they've recently gotten better. I attribute it to several things. Maybe he can test some of these to see if they help him.
1. There is something about the position of our couch: if I sit there I will have headaches later. I've heard reclining backward is not good.
2. If I am on the computer for too long, I will get a headache.
3. Sleep position - try to avoid sleeping on your stomach - it bends your neck. Ideally, sleep on your back if possible.
4. Diet - This is the hard one but if you are desperate enough like me, you will try anything. For just ONE WEEK, try eating no dairy, meat, or oil and see how you feel. For the first time in 1 1/2 years, I haven't needed Tylenol and Aleve around the clock. This is the 3rd day without medicine and I am really amazed. My head is still sensitive and I still need to be careful not to move too quickly and trigger it, but this is amazing. Some cookbooks with recipes are by Alan Goldhamer, Caldwell Esselstyn and John McDougal.
5. Sometimes fruit gives me a headache if I eat it on an empty stomach - so try eating it after something more substantial.
I hope he may be able to glean something helpful from this.