“Myth” or “Fact”

Abstract

One of the potential allures of nonrigid stabilization of the spine is the possibility that adjacent level disease could be eliminated or reduced. We explore whether this prospect is myth or fact. For spinal fusion, it is generally recognized that there is a definite risk of adjacent level degeneration. Ghiselli et al. have estimated that the rate of surgery for adjacent level disease was 3.9% for the 10 years following a primary lumbar fusion. Thus, at 10 years, the survivorship analysis predicted that 36.1% of lumbar fusion patients would have further operative intervention. Interestingly, their study also showed that the risk of adjacent level degeneration was significantly less for a multiple level fusion compared to a single segment arthrodesis. There is a limited amount of data available on the influence of pedicle screw-based stability/nonfusion technologies. Several authors have addressed the influence of disk arthroplasty on adjacent levels. Cunningham [31] looked at the biomechanics of TDA and found that the normal centrode of rotation was relatively maintained with TDA. In terms of motion, this would give TDA a favorable mechanical profile compared to fusion regarding shifting mechanical stresses to adjacent levels. Chang [32] performed disk pressure studies of adjacent levels in the cervical spine comparing TDA and fusion. Pressures were slightly lower at adjacent levels compared to fusion, except in flexion where pressures were higher with ProDisc–C. Longer-term follow-up is more available for lumbar TDA. David [34] has reported a 13.2-year follow-up of Charite. Lemaire [33] has an 8.7-year follow-up of ProDisc. Rates of symptomatic ASD varied between 1.9 and 2.6% for fusion, adjacent level disease is certainly Fact. One could argue this for lumbar TDA as well. For pedicle screw-based nonfusion technologies and cervical TDA, further time and studies will be required to bring issues out of the realm of myth.