Influence of Dynesys System Screw Profile on Adjacent Segment and Screw

Liu, Chien Lin; Zhong, Zheng Cheng; Shih, Shih Liang; Hung, Ching-Hua; Lee, Yong Eng; Chen, Chen Sheng

doi:10.1097/bsd.0b013e3181b63d89

Cited by 40 publications

(37 citation statements)

References 41 publications

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“…Our earlier study evaluated whether various depths of Dynesys screw placement would affect the biomechanical characteristics of the lumbar spine. We demonstrated that the profile of screw placement only had a minor influence on the ROM, annulus stress, and facet joint force, but that the screw stress was noticeably increased as the screw was moved further out of the pedicle [15].…”

Section: Introductionmentioning

confidence: 85%

Effect of the cord pretension of the Dynesys dynamic stabilisation system on the biomechanics of the lumbar spine: a finite element analysis

Liu

Zhong²,

Hsu³

et al. 2011

Eur Spine J

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The Dynesys dynamics stabilisation system was developed to maintain the mobility of motion segment of the lumbar spine in order to reduce the incidence of negative effects at the adjacent segments. However, the magnitude of cord pretension may change the stiffness of the Dynesys system and result in a diverse clinical outcome, and the effects of Dynesys cord pretension remain unclear. Displacement-controlled finite element analysis was used to evaluate the biomechanical behaviour of the lumbar spine after insertion of Dynesys with three different cord pretensions. For the implanted level, increasing the cord pretension from 100 to 300 N resulted in an increase in flexion stiffness from 19.0 to 64.5 Nm/deg, a marked increase in facet contact force (FCF) of 35% in extension and 32% in torsion, a 40% increase of the annulus stress in torsion, and an increase in the high-stress region of the pedicle screw in flexion and lateral bending. For the adjacent levels, varying the cord pretension from 100 to 300 N only had a minor influence on range of motion (ROM), FCF, and annulus stress, with changes of 6, 12, and 9%, respectively. This study found that alteration of cord pretension affects the ROM and FCF, and annulus stress within the construct but not the adjacent segment. In addition, use of a 300 N cord pretension causes a much higher stiffness at the implanted level when compared with the intact lumbar spine.

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Section: Introductionmentioning

confidence: 85%

Effect of the cord pretension of the Dynesys dynamic stabilisation system on the biomechanics of the lumbar spine: a finite element analysis

Liu

Zhong²,

Hsu³

et al. 2011

Eur Spine J

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“…Kim et al (35) observed through x-ray evaluation in 31 patients that the dynamic stabilization preserves only a limited motion, and may cause stress on the adjacent above level. Liu et al (13), through finite element analysis, evaluated the mechanical behavior of the lumbar spine after insertion of the Dynesys system: they found that under flexion and lateral bending, it alleviated annulus stress at the surgical level, but increased it at the adjacent level. In the same way, under extension, it decreased facet loading at the surgical level but increased facet loading at the adjacent level.…”

Section: Discussionmentioning

confidence: 99%

“…However, discordant findings were found using this treatment, as it did not always result in clinical improvement (7)(8)(9)(10)(11)(12). In fact a high incidence of accelerated disc degeneration at adjacent levels has been reported when patients were treated with a rigid instrumentation system (13)(14)(15).…”

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confidence: 98%

Mid‐term evaluation of the effects of dynamic neutralization system on lumbar intervertebral discs using quantitative molecular MR imaging

Ciavarro

Caiani

Brayda-Bruno

et al. 2011

Magnetic Resonance Imaging

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Purpose: To evaluate the mid-term effects of implant of dynamic neutralization system (Dynesys) on disc tissue in patients with lumbar discopathy, through the quantification of glycosaminoglycans (GAG) concentration, both in treated and adjacent levels, by analysis of delayed gadolinium-enhanced MRI contrast (dGEMRIC) images. Materials and Methods:Ten patients with low back pain underwent the dGEMRIC diagnostic protocol before, 6-months and after 2 years from surgery. Each patient was also evaluated with visual analog (VAS), Oswestry, and Prolo scales both at presurgery and during follow-up. From dGEMRIC images, a DT1 parametric map was obtained for each disc, as quantitative indicator of its GAG concentration, and divided in 13 sectors, which were classified at presurgery as normal or abnormal, based on a 70-ms threshold. Evolution of DT1 was studied during the follow-up.Results: Nine of ten patients completed the follow-up. VAS, Oswestry, and Prolo grades showed an improvement. This was accompanied by a reduction of DT1 in abnormal segments while normal segments showed a pattern of initial worsening at 6 months, followed by an improvement after 2 years. Conclusion:Our study confirmed the improvement in clinical evaluation, and for the first time related this to the changes in discs GAG concentration.

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“…7 Several researchers have investigated facet joint contact force in nonfusion dynamic stabilization, and the Dynesys system is reported to produce a greater facet contact force than that in the normal spine under all loading conditions. 11,14,16 A biomechanical FEM-based study of the Dynesys system at L4-5 showed that the facet contact force during extension increased with an increase in moment. 7 This undesirable effect on facet contact force would contribute to facet joint degeneration at the instrumented segment.…”

Section: Discussionmentioning

confidence: 99%

Facet joint changes after application of lumbar nonfusion dynamic stabilization

Lee

Jahng

Kim

2016

FOC

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OBJECTIVE The long-term effects on adjacent-segment pathology after nonfusion dynamic stabilization is unclear, and, in particular, changes at the adjacent facet joints have not been reported in a clinical study. This study aims to compare changes in the adjacent facet joints after lumbar spinal surgery. METHODS Patients who underwent monosegmental surgery at L4–5 with nonfusion dynamic stabilization using the Dynesys system (Dynesys group) or transforaminal lumbar interbody fusion with pedicle screw fixation (fusion group) were retrospectively compared. Facet joint degeneration was evaluated at each segment using the CT grading system. RESULTS The Dynesys group included 15 patients, while the fusion group included 22 patients. The preoperative facet joint degeneration CT grades were not different between the 2 groups. Compared with the preoperative CT grades, 1 side of the facet joints at L3–4 and L4–5 had significantly more degeneration in the Dynesys group. In the fusion group, significant facet joint degeneration developed on both sides at L2–3, L3–4, and L5–S1. The subjective back and leg pain scores were not different between the 2 groups during follow-up, but functional outcome based on the Oswestry Disability Index improved less in the fusion group than in the Dynesys group. CONCLUSIONS Nonfusion dynamic stabilization using the Dynesys system had a greater preventative effect on facet joint degeneration in comparison with that obtained using fusion surgery. The Dynesys system, however, resulted in facet joint degeneration at the instrumented segments and above. An improved physiological nonfusion dynamic stabilization system for lumbar spinal surgery should be developed.

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Influence of Dynesys System Screw Profile on Adjacent Segment and Screw

Cited by 40 publications

References 41 publications

Effect of the cord pretension of the Dynesys dynamic stabilisation system on the biomechanics of the lumbar spine: a finite element analysis

Effect of the cord pretension of the Dynesys dynamic stabilisation system on the biomechanics of the lumbar spine: a finite element analysis

Mid‐term evaluation of the effects of dynamic neutralization system on lumbar intervertebral discs using quantitative molecular MR imaging

Facet joint changes after application of lumbar nonfusion dynamic stabilization

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