When I saw your post this morning, my reaction was that I had already replied to it. But when I looked, I couldn't find a response. Then I remembered. I had written several paragraphs when I managed to make my response disappear into cyberspace...and I didn't have the heart to start over at that point...so, I apologize for not replying sooner.
Can you describe how the pain is different from what you had before?
I had a foraminotomy in between my two fusions and the results lasted a brief time. When I told my first surgeon about this when we ran into each other at a hardware store, he told me he no longer performs a foraminotomy as a "stand-alone" surgery because he found they just do not last. I suspect this is the problem with yours. In theory, it makes sense and should work to relieve the nerve compression, but sooner or later, the nerve becomes compressed again.
My reaction would be to go ahead and have the SI joint injected, figuring it probably won't hurt anything and just might be enough to get you over the hump. But I suspect you may have an issue with L4-L5 that is still compressing one or more spinal nerves.
Do you have another orthopedic spine surgeon you could see for another opinion, or are you comfortable with the neurosurgeon (Doc #3)?
It may be that the "bone spur" that the surgeon removed was really cartilage rather than bone, and for this reason, it didn't show up. It may be that the facet joint at this level was impinging on the nerve and he shaved off a little bit of it. The main reason for me having 3 surgeries was caused by degenerative facets that did not show up on MRIs.
Do you know the condition of your L5-S1 segment?
Sorry for all the questions...I'm just trying to think out of the box a bit.
Also...would it be possible for you to make some changes in your office so you could also working standing up? My husband is also a runner and almost 20 years ago he ruptured L5-S1. When he returned to work I remember going along to carry his briefcase! But he quickly realized that he was much better off when he stood up whenever he could...and on occasion he would close his door and conduct business while lying on the floor.
Sitting puts 30% more stress on the discs than other positions....so avoid as much as possible and break it up as often as you can by taking just a few steps back and forth...just to give the discs a little break.
When you get home try this form of natural traction:
Lie on the floor in a straight line, knees bent, feet flat on the floor. Place arms close to your sides with the palms facing upward toward the ceiling. Now, relax and breathe deeply from the belly, so your stomach rises and falls. Stay like this for 5 minutes, breathing deeply and relaxing.
This position allows the discs to decompress and get out from under the weight of gravity. I still do this twice a day, and if I've been working in the garden, or doing anything that I know will cause back pain, I automatically hit the floor and rest like this. I think it is what has kept me going!