The problem with fusion & instrumentation

Surgery to relieve the symptoms of a herniated disc involves removing some or all of the damaged disc. But something has to be inserted between the two vertebrae in the place of the disc tissue that is removed. For the majority of patients a spinal fusion is the typical surgery. A piece of bone is inserted and often a fixation plate holds the fusion in position. However, this is less than ideal in that two vertebrae are then locked together, which can stress other discs above and below. The artificial disc, conversely, is designed to retain natural motion.