ADR vs. fusion

I've been reading alot of studies comparing disc replacement to fusion. In a nutshell, ADR seems better in the very short term (<6 months) but things supposedly even out after that. At two years, there appears to be little difference in patient pain level and satisfaction. The presumed primary benefit of ADR is that degeneration of adjoining levels would be prevented due to the preservation of mobility, however that hypothesis is as yet unproven since ADR has not been around long enough. There is evidence to show that fusion does lead to adjacent segment degeneration (ASD) after a decade or so. At which point, I guess you just go in for another fusion...? And of course no one really knows the long-term prognosis of ADR.

The Ontario study is the best one I've read so far. Some selected excerpts:

Disadvantages of surgical fusion include loss of movement in the spine, which is thought to promote ASD. Adjacent segment degeneration is the degeneration of the vertebrae above or below the fusion site. It is thought that increased mobility of the adjacent vertebrae, as well as more pressure on the adjacent intervertebral discs as a result of motion transfer from the fused vertebrae may play a key role in the development of ASD. However, it is unclear if ASD is solely related to the spinal fusion process or to the natural degeneration of the vertebrae. The development of ASD is concerning because it can increase the need for additional surgery if it causes symptoms like pain and disability.

The surgical management of chronic low back pain due to DDD is still controversial, with inconsistent evidence to support its effectiveness. In a 2005 systematic review on surgical interventions for lumbar DDD, researchers were unable to determine the superiority of any one fusion technique or combination of techniques when compared with other types of surgical and nonsurgical interventions.

Unlike spinal fusion, ADR preserves movement of the spine, and this is thought to reduce or prevent the development of ASD. The surgical procedure for disc replacement involves an anterior approach for exposure of the spine, which predisposes the patient to vascular injury of the great vessels more so than does the posterior approach of spinal fusion. However, an anterior approach to fusion surgery is also an accepted method. Often a vascular surgeon is needed to carry out the anterior approach, while the actual disc replacement is completed by either an orthopedic surgeon or a neurosurgeon. Revision surgery for ADR is a complicated process because of the scarring around the great vessels from the initial surgery. It has been suggested that the artificial disc is unlikely to have the exact characteristics of the native vertebrae, and because of this different models can be expected to yield different long-term results. The long-term durability of artificial intervertebral discs is unknown.