I signed up for a study using a nerve stimulator inside my spinal cord. It's supposed to help reduce my back and leg pain by as much as 50 per cent. The brochure says some people aren't eligible for this treatment. How do they decide who is and who isn't eligible?
You may be referring to a spinal cord stimulator (SCS). This device is also called a dorsal column stimulator.It is an implanted electronic device used to help treat chronic pain.

The device delivers a low level electrical current through wires placed near the spinal cord. The pulse generator is about the size of a 50-cent piece.

The spinal cord stimulator will not cure your pain. Most people report at least a 50 percent decrease in pain. This should allow you to be more active. The need for less pain medication is also considered a successful result. Before having the device implanted, a trial is done with an external device for about a week.

If you do not obtain at least a 50 per cent decrease in painful symptoms, then you may not be eligible for internal implantation. Other factors that may be considered are the ability to operate the system or a psychiatric condition that might affect your ability to use the device.

A past history of blood clots may prevent your participation in the study. The presence of other health problems or conditions may exclude you. This can include conditions such as diabetes, arthritis, or lupus. Each study will have its own eligibility requirements. You can ask whoever is setting up the study what are their eligibility and exclusion categories.