Flexible rods and the case for dynamic stabilization

Abstract

<jats:p>✓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.</jats:p> <jats:p>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.</jats:p> <jats:p>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 inter-body 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.</jats:p> <jats:p>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.</jats:p>

Posterior dynamic stabilization for the treatment of patients with lumbar degenerative disc disease: long-term clinical and radiological results

“…Our understanding of the symptoms of discogenic pain has deepened with the increased resolution available in MRI, the development of new techniques in lumbar disc surgery, the emergence of new concepts regarding the ability to use bone morphogenetic proteins, and detailed research on the results of lumbosacral fusion (1,2,4,7,(15)(16)(17)20,22,23,(25)(26)(27)29,30,33).…”

“…These systems are suitable for the treatment of instability in each of the three columns and can also be used prophylactically in cases that can develop instability or in the treatment of instability as a result of painful black disc, degenerative spondylolisthesis, recurrent disc herniation, and lumbar canal stenosis treatment (11,16,20,23,26,29,32). It has low complication risks, and its revision is easy.…”

“…During the long-term follow-up period, the occurrence of further degeneration and instability as a result of increased mobility in the segments adjacent to fused spinal segments is an undesirable outcome. As a result, stabilization systems have become more physiological overtime (7,11,15,16,18,20,22,23,28,32).…”

“…The instrumentation used in dynamic stabilization is designed to control the amount of motion between adjacent vertebrae, but it does not completely eliminate this movement. Posterior dynamic stabilization is an ideal technique for providing stabilization in cases of chronic instability (4,7,11,15,16,18,20,22,23,29,30). The goals of the dynamic stabilization procedure are to control the neutral posture of the segment, control sagittal plane bending of the treated vertebra, unload the intervertebral disc at the treated level, and modify the distribution of loads within the segment, in particular within the intervertebral disc.…”

“…Fusion surgery of the spine is accomplished by stimulating bone to grow between two or more adjacent spinal segments, thus preventing future motion. To allow for continued mobility at the level that the patient is accustomed to in daily life, the load from immobilized segment angles is distributed to the other segments (2,11,13,16). This in turn results in accelerated degeneration, especially in the adjacent vertebrae, as shown by several studies.…”