I'm so sorry to hear that your husband is back in the hospital and having so many problems.
It still sounds like the scar tissue is wrapping around nerves and causing the pain.
I would think that the steroids are helping because of their strong anti-inflammatory affect that they have in the body.
Foot drop can come from the nerve compression.
If these doctors can't find what the cause of his pain is, you really, really need to get some other opinions from other spine surgeons.
Obviously there is a cause for the pain and you have an MRI that show scar tissue buildup.
It should be obvious to them that this is or may very well be the cause of his pain, yet they are saying they don't know what is causing the pain.
If the pain is nerve pain then pain meds really won't help him.
Have they started him on any meds for nerve pain, either Neurontin or Lyrica?
That is something he should be taking to help ease the pain from nerve pain.
Signs of Cushing Syndrome from the steroids is not good, and he will have to stop taking them.
Please consult some other spine surgeons that are not part of the practice that your husband's present spine surgeons are part of.
Preferably consult with spine surgeons that are not part of the hospital that he is in as well.
Doing both of those will give you a real different opinion and not one that is tied to the present doctors and hospital.
Good luck and keep us posted.
Fran