Had Lumber Fusion. Have Chronic Pain. Need Surgery?
During the 360 degree fusion, it is during the anterior approach the large veins and arteries of the abdomen, especially the iliac vessels/aorta or the inferior vena cava which are close. Therefore, usually removing the posterior hardware should not place these vessels at risk.
I presume your doctor must have looked at scans and X-rays and has offered to remove the hardware, if there is a possibility of the pain being caused due to the hardware. Unfortunately, most of the time it is difficult to know how much one single factor is the cause of the backache. The muscle atrophy and scarring happens due to the fact that the back has to be opened and the muscles stretched in order to put in the metalwork. The metalwork itself is not the direct cause of paraspinal muscle atrophy/scaring.
Once the posterior metalwork has been removed, your doctor/surgeon will reassess your condition after you have recovered from the surgery and start getting back on your feet. At that time, he/she will also explore the suitability of other pain reliving procedures like intrathecal drug infusion pumps and spinal cord stimulation. This would be done in consultation with the Pain specialist.
I have given this answer assuming your fixation has been in the lumbo-sacral region. Hope this has answered your questions.
If you have any other questions or any further clarifications are needed please get back to me.