Flexible rods and the case for dynamic stabilization

Abstract

The widespread use of instrumentation in the lumbar spine has led to high rates of fusion. This has been accompanied by a marked rise in adjacent-segment disease, which is considered to be an increasingly common and significant consequence of lumbar or lumbosacral fusion. Numerous biomechanical studies have demonstrated that segments fused with rigid metallic fixation lead to significant amounts of supraphysiological stress on adjacent discs and facets. The resultant disc degeneration and/or stenosis may require further surgical intervention and extension of the fusion to address symptomatic adjacent-segment disease. Recently, dynamic stabilization implants and disc arthroplasty have been introduced as an alternative to rigid fixation. The scope of spinal disease that can be treated with this novel technology, however, remains limited, and these treatments may not apply to patients who still require rigid stabilization and arthrodesis. In the spectrum between rigid metallic fixation and motion-preserving arthroplasty is a semirigid type of stabilization in which a construct is used that more closely mirrors the modulus of elasticity of natural bone. After either interbody or posterolateral arthrodesis is achieved, the fused segments will not generate the same adjacent-level forces believed to be the cause of adjacent-segment disease. Although this form of arthrodesis does not completely prevent adjacent-segment disease, the dynamic component of this stabilization technique may minimize its occurrence. The authors report their initial experience with the use of posterior dynamic stabilization in which polyetheretherketone rods were used for a posterior construct. The biomechanics of dynamic stabilization are discussed, clinical indications are reviewed, and case studies for its application are presented.