The plan, however, is for one of the bullet fragments to have ended up in the spinal canal somewhere in the lumbar spin--only pressing against the spinal cord, not particularly injuring it. Character A might have some clumsiness or pain, more at first thanks to swelling, but compared to the pain and trouble recovering from major abdominal surgery, it's minimal, and he knows the fragment is in there, so it's not going to be a big deal up to this point. However, later in the story, (this is a pretty long-term plot, it takes place over a minimum of five years) the fragment starts to migrate, causing problems; pain, possible urinary and/or fecal incontinence, trouble walking, etc... depending on what vertebral space I end up using. Not so much enough to really disable the character, or if so, definitely not to a wheelchair-requiring level, but enough to be very annoying, frustrating, and be something both characters have to deal with in their daily lives.
Would they have left the fragment in there? The idea was that it would have been more of a risk to try and operate on such a delicate area than to leave it in there. Is this possible/accurate? ( Irelize that this is a very case-by-case sort of thing, but just in general, would it be reasonably likely.)
If it's not really possible to generalize on the above question, what would be the criteria for removal/non-removal
Would they have done anything to immobilize the area to prevent migration? (Brace, pins, anything?)
How fast/much would the bullet migrate? Does it make sense for it to have stayed relatively put for at a very minimum of several months, and then start to migrate? Does it make sense for it to continue to migrate, probably affecting different sections of the spinal cord at different times throughout the years the story is set in?
How much of the damage would be caused by the actual presence/migration of the fragment versus the toxic effects of the lead/copper/aluminum that the bullet was made out of? (I've read that copper does cause toxic effects to surrounding spinal nerve tissue in this kind of situation, and I know lead causes brain issues when in the blood stream, but other than that, I haven't found much about this at all)
Googled: Bullet fragment in spine, toxic effects from bullet metals, spinal injury, and various similar terms and combinations
(this: http://www.spine-dr.com/site/surgery/surgery_mib.html was very helpful, and did answer many questions I had, just not these)