@kmf Thank you for further details. I can understand why the doctors are focusing on the issues that could affect your heart because the heart gets priority over everything. What I wonder about is why your symptoms change with different body positions? Have they confirmed if the fusion process has started? By 9 months post op, it should have, but sometimes there may be a non union. If there is any instability of other vertebrae that can slip or move position, that may be a clue. I also think about possible changes in circulation that may bring about symptoms since you said your leg feels swollen.

Have the doctors done x-rays in these positions to check if your spine is actually fused or to look for any hardware failures and if change of position changes spine alignment? Likewise, a Doppler study on circulation can show if your circulation is being diminished or if there could be a deep vein thrombosis or if there are circulation changes with different body positions. I have a situation where that happens because of my arm position with Thoracic Outlet Syndrome. There could be a similar issue with the lower limbs. Those would be simple tests to request if not done already. If you have an online patient portal with your medical system, you may want to read your medical records and look up everything. That will tell you what your doctors are thinking.

Here are a few links to information that may be useful for information.
https://mskneurology.com/chronic-spinal-pain-and-radiculopathy-diagnostic-approach-and-common-imaging-pitfalls/
https://mskneurology.com/identify-treat-lumbar-plexus-compression-syndrome-lpcs/
I can also tell you that one way to find specialists is to look for medical research papers and look to see who the authors are and authors of other literature that is cited. That will take a long time, but you may find some experts who understand complex situations. If you start looking up terminology in your medical records, you may find literature about similar cases.

I was also able to find this on the Mayo website with an Information Service office for Canada you can call with questions, but not medical visits.
https://www.mayoclinic.org/departments-centers/international/locations/canada
Jennifer