I see Danimal answered with much of the same information, but I wrote all of this earlier and forgot to hit submit. Seems a shame to waste it, so *submit*
The SCS doesn't interfere with fusion hardware, artificial disks, etc. directly. Keep in mind is that the SCS leads are typically placed at a healthy area of your spinal cord, not
at the injury site or problem area of your spine. For example, the majority of people that have an SCS implanted for lumbar problems find their leads placed in the thoracic spine - T8 through T12. My issues are mainly L4/L5/S1 and normally, my doctor said he'd place the leads for that area between T10-T12. I have some non-symptomatic disk issues in that area too, so my leads are placed at T7-T8.
The problem with defibrillators is that the leads can pick up the electric charge, transmit it backwards, and damage the impulse generator. The FDA requires the implant manufacturers to advise patients and doctors of any device that can cause damage to the system or that the system make interfere with. As far as defibrillation goes, the stimulator and leads have potential to interfere with the function of the defibrillator and that's the most important reason for the warnings - you must always carry the card so that emergency medical personnel can make any adjustments required to render effective care to you (i.e. turn off the stimulator if you're unable, change settings on their equipment, etc.) As far as letting you die because of the device, Medtronic states clearly in multiple places in their literature (including the patient instruction manual) that preserving the life of the patient is the primary concern, and repairing any damage to the system is secondary.
To answer the first part - if your doctor needs imaging of your spine and you have an SCS, they will most likely turn to the CT scanner.
I'm assuming by NMR, you're referring to magnetic resonance imaging. I recently had a long discussion about
this topic with my doctor.
The reason you can't have an MRI with the SCS implant is because of the electromagnetic field created by the scanner; the pulse generator and the lead wires absorb heat during the scanning process and rise to a temperature that literally burns and destroys the tissue around them. Even when doctors explant an SCS system, they rarely remove the lead wires entirely; typically, they remove the IPG, remove the electrode ends of the leads, but they leave the wires along the tunnel intact because removing the wire from the scar tissue would require an incredibly invasive surgery for very little actual benefit. And, unless you've had every single bit of the SCS system removed, the MRI remains off limits because the remaining pieces of the lead wires will still conduct heat.
I asked my doctor specifically what we'd do if he needed
another MRI of my spine. He sort of laughed and said that needing
an MRI is a very relative thing. His explanation of that was to tell me that the MRI scan is a lot like "one stop shopping" at Walmart. You can get what you need, all in one store, and the price is pretty good when you look at the average cost per item, and you're in and out pretty quick. What people tend to forget is that with a little more effort, you can also get all the same things at several little Mom & Pop shops, but you might pay a little higher cost per item, drive a little farther, and it'll take a bit longer. Either way, when you're done shopping, you have what you need to make dinner. Doctors can run a single MRI and obtain a lot of information (i.e. Walmart), but people fail to realize an MRI isn't the only
way we can get that information; it can also be obtained through a combination of other diagnostic tests (i.e. Mom & Pop Shops).