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Study design:Comparative effectiveness review.
Study rationale:Spinal fusion is believed to accelerate the degeneration of the vertebral segment above or below the fusion site, a condition called adjacent segment disease (ASD). The premise of dynamic stabilization is that motion preservation allows for less loading on the discs and facet joints at the adjacent, non-fused segments. In theory, this should decrease the rate of ASD. However, clinical evidence of this theoretical decrease in ASD is still lacking. We performed a systematic review to evaluate the evidence in the literature comparing dynamic stabilization with fusion.
Clinical question:In patients 18 years or older with degenerative disease of the cervical or lumbar spine, does dynamic stabilization lead to better outcomes and fewer complications, including ASD, than fusion in the short-term and the long-term?
Methods:A systematic search and review of the literature was undertaken to identify studies published through March 7, 2011. PubMed, Cochrane, and National Guideline Clearinghouse Databases as well as bibliographies of key articles were searched. Two individuals independently reviewed articles based on inclusion and exclusion criteria which were set a priori. Each article was evaluated using a predefined quality-rating scheme.
Results:No significant differences were identified between fusion and dynamic stabilization with regard to VAS, ODI, complications, and reoperations. There are no long-term data available to show whether dynamic stabilization decreases the rate of ASD.
Conclusions:There are no clinical data from comparative studies supporting the use of dynamic stabilization devices over standard fusion techniques.
Spinal fusion is believed to accelerate the degeneration of the vertebral segment above or below the fusion site, a condition called adjacent segment disease (ASD).1 Dynamic stabilization systems have increased in popularity in the past decade as an alternative to fusion for treatment of degenerative spine conditions. In theory, they allow for less loading on the adjacent discs and facet joints and preserve adjacent segmental motion. Theoretically, this should lead to a decrease in ASD. However, it is unclear that such devices lead to better outcomes compared with traditional fusion, and it is unclear if it truly leads to a decrease in ASD.
In patients 18 years or older, with degenerative disease of the cervical or lumbar spine, does dynamic stabilization lead to better outcomes and fewer complications, including ASD, than fusion in the short-term and long-term?
Study design: Comparative effectiveness review.
Search: PubMed, EMBASE, Cochrane Database of Systematic Reviews, bibliographies of key articles.
Dates searched: up through March 7, 2011.
Inclusion criteria: Studies directly comparing dynamic stabilization devices with traditional fusion (CoE I–III) in patients 18 years or older with degenerative spine disease (including spinal stenosis, spondylosis, spondylolisthesis, and/or degenerative disc disease).
Exclusion criteria: Studies in patients younger than 18 years, those with tumors, trauma, primary infection or inflammatory cause, fracture, Paget disease, osteochondrosis, congenital malformation, or visceral diseases, or previous lumbar surgery; studies comparing single versus multilevel dynamic stabilization without a comparison arm for fusion; studies of interspinous spacers (as sole device), dynamic devices, case series, non-human in vivo, in vitro, and biomechanical studies.
Outcomes: Visual analogue scale (VAS) for low back and lower leg pain; Oswestry disability index (ODI); ASD, reoperation, and other complications.
Analysis: Means and information on variation (eg, standard deviation or range) for continuous variables were abstracted from the report as available or if necessary, estimated from author figures and change scores calculated. The mean percentage improvement in the outcome score from baseline at each given follow-up time was calculated by dividing the change score by the baseline score to get the total percentage improvement. Rates of ASD, reoperation, and complications were calculated. Pooling of data was not done due to concerns regarding heterogeneity of treatments and populations as well as study quality.
Additional methodological and technical details are provided in the electronic supplemental material at www.aospine.org/ebsj.
Most published reports were case series, in vitro or biomechanical studies. From a total of 79 citations retrieved, 14 were selected for full-text review (Fig. 1). Of these, five met the inclusion criteria; however, duplicate papers on the same population were found2,3 and the most updated study was included for analysis.2 Thus, four relatively small comparative studies are critically summarized,2,3,4,5 three of which were prospective. Populations were predominantly female (Table 1). Different dynamic stabilization systems were used including: the Cosmic dynamic pedicle screw-rod system, Twinflex rod system, Interspinous Soft Stabilization (ISS) with tension band system, and dynamic (hinged) pedicle screws (Table 2). All studies are class of evidence III.
Further details on the class of evidence rating for these studies can be found in the supplemental material at www.aospine.org/ebsj.
Adjacent segment disease (Table 5)
Reoperation (Table 5)
Other complications (Table 5)
|Pain and disability|
|Outcomes||Strength of evidence||Conclusions/comments|
|1. VAS–back pain|
|2. VAS–leg pain|
|Outcomes||Strength of evidence||Conclusions/comments|
|3. Other complications|
Conclusions from this review are limited by the following:
This article was funded by AOSpine.
The controversy surrounding the role and actual function of so-called “dynamic” fixation devices was reflected in the reviewers' comments. The devices in question are different from one another and defy simple biomechanical categorization. Their ability to provide long-term stabilization of a damaged operated-on segment remains to be seen–toggle loosening, implant breakage, foreign body reactions all await further clarification.
The other question that remains unanswered: Are patients with dynamic stabilization devices still mobile in their target level, or did they in fact inadvertently fuse? As more of these devices push on the market, a comparative biomechanical analysis using variety of loading mechanisms, including load to failure and fatigue loading together with monitoring of adjacent segment disc mechanics would appear to be a helpful first step to allow clinicians to understand the effects of the devices that are being offered for implantation. Again, at this time the basic first step, indications remain unclear. Then, the same can be said for the phenomenon of ‘adjacent disc disease.’ Is it patient borne, surgeon created, or a mixture of both? It is this first step that we need to understand before we can move ahead and try to identify preventative variables.