Every segment of the spinal column permits a small amount of motion through the intervertebral disc and the facet joints. This allows for flexion and extension, lateral flexion, and some rotation. These movements, when combined over many segments, allow for all of our usual daily activities to be performed. Whenever possible, artificial discs are preferred over fusion operations to preserve this motion. However, if the primary problem is with instability or abnormal motion, then a fusion may well be the most appropriate intervention.