Safety is always a key concern whenever spinal surgery is done. Damage to nerves or even the spinal cord is possible. The result can be permanent loss of sensation and/or motor function. Surgeons do everything they can to avoid neurologic problems.
Surgeons doing disc replacements should have a lot of practice with spinal surgery before replacing discs. The anterior approach (from the front) is better than a posterior approach (from the back). Using the anterior approach, the surgeon is less likely to damage the blood vessels, nerves, and spinal cord.
Some surgeons ask for help from a general or vascular surgeon to prevent these kinds of problems. They can also use a special device to monitor for any changes in spinal cord function during the operation. The overall complication rate is very low for this operation.