existed in Europe. Since then, the initial excitement has given way to skepticism and concern. Various failure rates and strategies for revision of total disc replacement have been reported. The role of artificial or total disc replacement in the treatment of spinal disorders remains ill-defined and unclear. Evaluation of any new technique is difficult or impossible because physician experience may be minimal or lacking. Patient expectations may be distorted. It has been difficult to establish clear cut indications for artificial disc replacement. It may not be a replacement procedure or alternative to fusion, since recent studies have shown that 100% of fusion patients had one or more contraindications to disc replacement. The role of disc replacement must come from new indications not defined in today's literature or a relaxation of current contraindications. A study by Regan found the result of replacement was the same at L4-5 and L5-S1 with the CHARITE disc. However, the ProDisc II had more favorable results at L4-5 compared with L5-S1. A younger age was predictive of a better outcome in several studies. In others it has been found to be a negative predictor or of no predictive value. Older patients may have more complications. Prior spinal surgery has mixed effects on disc replacement. It has been reported to be negative in several studies. It has been reported to have no effect in other studies. Many studies are simply inconclusive. Existing evidence does not allow drawing definite conclusions about the status of disc replacement at present. Electrical stimulation Many failed back patients are significantly impaired by chronic pain in the back and legs. Many of these will be treated with some form of electrical stimulation. This can be either a transcutaneous electrical nerve stimulation device placed on the skin over the back or a nerve stimulator implanted into the back with electrical probes which directly touch the spinal cord. Also, some chronic pain patients utilize fentanyl or narcotic patches. These patients are generally severely impaired and it is unrealistic to conclude that application of neurostimulation will reduce that impairment. For example, it is doubtful that neurostimulation will improve the patient enough to return to competitive employment. Neurostimulation is palliative. TENS units work by blocking neurotransmission as described by the pain theory of Melzack and Wall. Success rates for implanted neurostimulation has been reported to be 25% to 55%. Success is defined as a relative decrease in