Dynamic Stabilisation Systems

Conventional fusion stops movement at a spinal segment by joining the vertebrae with rigid rods and, usually, a bone graft. The theoretical concern with fusion is that removing movement at one level may load the segments above and below. Dynamic stabilisation attempted to occupy a middle ground: screws are placed into the vertebrae as in a fusion, but they are connected by a flexible system intended to allow controlled, limited movement rather than rigid locking. The hope was to relieve pain from an unstable segment while avoiding both the stiffness of fusion and the loading of adjacent levels. It is a reasonable-sounding idea, and that is exactly why it attracted interest.

Here the picture is not encouraging. There are very few high-quality randomised trials. Most of the literature consists of retrospective series and meta-analyses of low-quality studies. Where dynamic stabilisation has been compared with fusion, the results are broadly comparable at best — that is, it does not clearly outperform fusion — and some studies have reported worse outcomes than fusion. Reviews of complications describe screw loosening as a recognised problem, and detailed studies have shown that the "dynamically stabilised" segment often stiffens and effectively fuses anyway over time, which undermines the whole rationale of preserving motion. Positional MRI studies confirm that these systems reduce, but do not abolish, segmental movement. The fair summary is that dynamic stabilisation has not been shown to be superior to the alternatives, that its central promise of durable motion preservation is doubtful, and that it carries its own device-specific problems.

Several factors keep this subject unsettled. The trials that exist are small and often of modest quality; the devices have evolved and been marketed under several names, making the literature hard to compare; and the outcome that matters most — protection of the adjacent segments over many years — is precisely the one that short and medium-term studies cannot answer. When a technology's main theoretical advantage cannot be demonstrated, and independent studies are lukewarm or negative, caution is the appropriate response.

I do not use dynamic stabilisation systems. My reasoning is straightforward: I am not persuaded that they offer a reliable advantage over well-established treatments, the evidence base is weak, and the concept's key benefit — lasting preservation of movement — appears not to hold up. This is not a criticism of every patient who has one of these devices, nor a claim that they never help anyone; it is an honest reflection of where the evidence stands. Patients considering such a device deserve to know that it is a contested option, not a proven one.

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• —Lee CH, et al. Neurosurg Focus. 2016. Meta-analysis: comparable outcomes, no clear adjacent-segment advantage. PMID 26721581
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• —Zhou LP, et al. BMC Surg. 2023. Medium/long-term meta-analysis vs instrumented fusion. PMID 36855117
• —Pham MH, et al. Neurosurg Focus. 2016. Review of Dynesys complications including screw loosening. PMID 26721576
• —Fay LY, et al. Neurosurg Focus. 2016. Dynesys segment often fuses; motion not truly preserved. PMID 26721578
• —Haddad B, et al. Acta Orthop Belg. 2013. Dynesys gave worse outcomes than fusion at 4 years. PMID 23547523
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• —Peng BG. World J Clin Cases. 2020. Editorial questioning whether Dynesys is superior to fusion. PMID 33344539
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