Hello, and I am glad to see you're pursuing information before undergoing surgery. I guess my question is what test is your decision going to be based on. According to your question, it appears that you're speaking about a series of 3 X-rays which can be good for diagnosing some issues, but definitely not appropriate for making the type of decision you are speaking of.
An appropriate pre-surgical test for any back surgery would be an MRI of the neck as well as the lumbar spine. This is the only test that's going to allow the physician to get a true idea of any narrowing of the spinal canal, as well as any disc issues. The reason I mention the neck or cervical spine, is that this would be the location of any issues in your spine that would cause arm numbness. I would be concerned about the loss of bowel and bladder function, and would pursue these issues with your physician at your earliest convenience.
I hope this answers your question, but if you'd like further clarification, or have more questions, please feel free to let me know. Best wishes...
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