Spine surgery can be remarkably effective at reducing or eliminating chronic pain. By far, the primary reason that patients consult with Dr. Lipani for revision spine surgery is that they continue to experience pain after their procedure.  Often, the reason for this continued pain is that the initial surgery operated on a structural issue that was not the direct cause of nerve compression.
Some of the reasons for failed back surgery include:
Failure of spinal structure to properly fuse.
Recurrent spinal stenosis or disc herniation after decompression surgery.
Inadequate decompression of the nerve root.
Scar tissue formation around a nerve root.
Continued pain originating from a secondary generator.
Spinal surgery is nuanced in nearly every situation. The term "failure" doesn't ascribe blame to the patient or doctor in most cases but is simply a matter of inadequate healing based on numerous physiological factors.