Re: Sacroiliac joint dysfunction - numbness in toes/feet?
You really should talk to your spine specialist about the pain and show them exactly where the pain is on your back. As you said you had a spine specialist, I assume they are either a neurosurgeon or orthosurgeon rather than neurologist who does no surgery. It is possible that you need another test, but again they may look more intently at the MRI films, concentrating on the lumbar area after you tell them of the pain you are experiencing. There are other diagnostic tests that could be needed, but first a good comprehensive exam with you showing them where your pain is. It is quite possible that you have some stenosis or other problems in the sacral area, around the L5-S1 or even at the S2 area.
You may also wish to visit the spine-universe site which is BionicWitch posted for board members to see. It is at the top of the threads in a post about "good news for lots of you" and has the exact link as approved by the moderators. The site is excellent and if you will do a site search for " Neurological.Exams.Sensory.Nerves" you should find an article there of a longer name which displays chart or list of which nerves cause pain/numbess at which locations. Gives you a pretty good idea of what area is causing which pain.
Best wishes and hope you will cover all the bases with your spine specialist.