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

Liu, Chien Lin; Zhong, Zheng Cheng; Hsu, Hung Wei; Shih, Shih Liang; Wang, Shih Tien; Hung, Ching-Hua; Chen, Chen Sheng

doi:10.1007/s00586-011-1817-3

Cited by 60 publications

(54 citation statements)

References 26 publications

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“…These studies also indicate that the high stiffness of the Dynesys system itself may be a major contributing factor to disc stress. Our previous study implanted with the Dynesys system [23] demonstrated that reducing the preload on the cord can alleviate stress of the disc and improve ROM at the adjacent levels during flexion. In a subsequent study, we changed the stiffness of the spacers by altering their diameter [24], and showed that spacers with smaller diameters reduce disc stress and ROM at adjacent levels during extension.…”

Section: Discussionmentioning

confidence: 99%

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Effects of cord pretension and stiffness of the Dynesys system spacer on the biomechanics of spinal decompression- a finite element study

Shih

Liu

Huang

et al. 2013

BMC Musculoskelet Disord

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BackgroundThe Dynesys system provides stability for destabilized spines while preserving segmental motion. However, clinical studies have demonstrated that the Dynesys system does not prevent adjacent segment disease. Moreover, biomechanical studies have revealed that the stiffness of the Dynesys system is comparable to rigid fixation. Our previous studies showed that adjusting the cord pretension of the Dynesys system alleviates stress on the adjacent level during flexion. We also demonstrated that altering the stiffness of Dynesys system spacers can alleviate stress on the adjacent level during extension of the intact spine. In the present study, we hypothesized that omitting the cord preload and changing the stiffness of the Dynesys system spacers would abate stress shielding on adjacent spinal segments.MethodsFinite element models were developed for - intact spine (INT), facetectomy and laminectomy at L3-4 (DEC), intact spine with Dynesys system (IntDyWL), decompressed spine with Dynesys system (DecDyWL), decompressed spine with Dynesys system without cord preload (DecDyNL), and decompressed spine with Dynesys system assembled using spacers that were 0.8 times the standard diameter without cord pretension (DecDyNL0.8). These models were subjected to hybrid control for flexion, extension, axial rotation; and lateral bending.ResultsThe greatest decreases in range of motion (ROM) at the L3-4 level occurred for axial rotation and lateral bending in the IntDyWL model and for flexion and extension in the DecDyWL model. The greatest decreases in disc stress occurred for extension and lateral bending in the IntDyWL model and for flexion in the DecDyWL model. The greatest decreases in facet contact force occurred for extension and lateral bending in the DecDyNL model and for axial rotation in the DecDyWL model. The greatest increases in ROMs at L2-3 level occurred for flexion, axial rotation and lateral bending in IntDyWL model and for extension in the DecDyNL model. The greatest increases in disc stress occurred for flexion, axial rotation and lateral bending in the IntDyWL model and for extension in the DecDyNL model. The greatest increases in facet contact force occurred for extension and lateral bending in the DecDyNL model and for axial rotation in the IntDyWL model.ConclusionsThe results reveals that removing the Dynesys system cord pretension attenuates the ROMs, disc stress, and facet joint contact forces at adjacent levels during flexion and axial rotation. Removing cord pretension together with softening spacers abates stress shielding for adjacent segment during four different moments, and it provides enough security while not jeopardizes the stability of spine during axial rotation.

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Section: Discussionmentioning

confidence: 99%

“…In our previous study we examined the effect of different cord preloads on the Dynesys system [23] and revealed that high stiffness was related to high preloads of approximately 300 N on the cord. We also demonstrated that preloads as low as 100 N can reduce facet joint contact forces and disc stress at adjacent levels during flexion.…”

Section: Introductionmentioning

confidence: 99%

Effects of cord pretension and stiffness of the Dynesys system spacer on the biomechanics of spinal decompression- a finite element study

Shih

Liu

Huang

et al. 2013

BMC Musculoskelet Disord

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“…29 The use of a 300-N cord pretension causes a much higher stiffness at the implanted level than the intact lumbar spine. 20 Because the effects of spacer length and cord tension on segmental flexibility and rigidity are still debated in the literature, many surgeons adjust the pretension below 300 N depending on the patient's condition. 24,32 Other advantages of the Dynesys system are that the procedure to implant it is less invasive than PLIF and it results in earlier recovery.…”

Section: Evaluation Of Possible Advantages Of the Dynesys Systemmentioning

confidence: 99%

Dynamic stabilization using the Dynesys system versus posterior lumbar interbody fusion for the treatment of degenerative lumbar spinal disease: a clinical and radiological outcomes-based meta-analysis

Lee

Jahng

Hyun

et al. 2016

FOC

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OBJECTIVE The Dynesys, a pedicle-based dynamic stabilization (PDS) system, was introduced to overcome the drawbacks of fusion procedures. Nevertheless, the theoretical advantages of PDS over fusion have not been clearly confirmed. The aim of this study was to compare clinical and radiological outcomes of patients who underwent PDS using the Dynesys system with those who underwent posterior lumbar interbody fusion (PLIF). METHODS The authors searched PubMed, Embase, Web of Science, and the Cochrane Database. Studies that reported outcomes of patients who underwent PDS or PLIF for the treatment of degenerative lumbar spinal disease were included. The primary efficacy end points were perioperative outcomes. The secondary efficacy end points were changes in the Oswestry Disability Index (ODI) and back and leg pain visual analog scale (VAS) scores and in range of motion (ROM) at the treated and adjacent segments. A meta-analysis was performed to calculate weighted mean differences (WMDs), 95% confidence intervals, Q statistics, and I2 values. Forest plots were constructed for each analysis group. RESULTS Of the 274 retrieved articles, 7 (which involved 506 participants [Dynesys, 250; PLIF, 256]) met the inclusion criteria. The Dynesys group showed a competitive advantage in mean surgery duration (20.73 minutes, 95% CI 8.76–32.70 minutes), blood loss (81.87 ml, 95% CI 45.11–118.63 ml), and length of hospital stay (1.32 days, 95% CI 0.23–2.41 days). Both the Dynesys and PLIF groups experienced improved ODI and VAS scores after 2 years of follow-up. Regarding the ODI and VAS scores, no statistically significant difference was noted according to surgical procedure (ODI: WMD 0.12, 95% CI −3.48 to 3.72; back pain VAS score: WMD −0.15; 95% CI −0.56 to 0.26; leg pain VAS score: WMD −0.07; 95% CI −0.47 to 0.32). The mean ROM at the adjacent segment increased in both groups, and there was no substantial difference between them (WMD 1.13; 95% CI −0.33 to 2.59). Although the United States is the biggest market for Dynesys, no eligible study from the United States was found, and 4 of 8 enrolled studies were performed in China. The results must be interpreted with caution because of publication bias. During Dynesys implantation, surgeons have to decide the length of the spacer and cord pretension. These values are debatable and can vary according to the surgeon's experience and the patient's condition. Differences between the surgical procedures were not considered in this study. CONCLUSIONS Fusion still remains the method of choice for advanced degeneration and gross instability. However, spinal degenerative disease with or without Grade I spondylolisthesis, particularly in patients who require a quicker recovery, will likely constitute the main indication for PDS using the Dynesys system.

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“…A three-dimensional nonlinear FE model of the human lumbar spine was created using the commercial software ANSYS 11.0 (ANSYS Inc., Canonsburg, PA, USA) in our previous studies [18,19]. Much of detailed description for this lumbar spine FE model had been reported [19,20].…”

Section: Validation Of the Fe Modelmentioning

confidence: 99%

“…The DY [18,24] and the KD models ( Fig. 2) were bilaterally inserted into the L3-L4 level of the model.…”

Section: Fe Model Of the Dy And Kd Systemsmentioning

confidence: 99%

Biomechanical comparison of the K-ROD and Dynesys dynamic spinal fixator systems – A finite element analysis

Lin

Pan

Liu

et al. 2013

Bio-Medical Materials and Engineering

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Dynamic spinal fixators, such as the Dynesys (DY) and K-ROD (KD) systems, are designed to restore spinal stability and to provide flexibility. The long-term complications of implant breakage and the biomechanics of the adjacent and the bridged levels using the KD system are still unknown. Therefore, this study aims to investigate and compare the biomechanical effects of the KD system and the DY system. Finite element (FE) models of the degenerated lumbar spine, the DY system, and the KD system were each reconstructed. Hybrid-controlled analysis was applied in the three FE models. The FE results indicated that the KD system supplies the most stiffness during extension and the least stiffness during flexion, in contrast to the DY system. In contrast to the DY system, the KD system increased the facet contact force of the adjacent level, but this system decreased the screw stress on the cranial adjacent disc and the pedicle during flexion.

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

Cited by 60 publications

References 26 publications

Effects of cord pretension and stiffness of the Dynesys system spacer on the biomechanics of spinal decompression- a finite element study

Effects of cord pretension and stiffness of the Dynesys system spacer on the biomechanics of spinal decompression- a finite element study

Dynamic stabilization using the Dynesys system versus posterior lumbar interbody fusion for the treatment of degenerative lumbar spinal disease: a clinical and radiological outcomes-based meta-analysis

Biomechanical comparison of the K-ROD and Dynesys dynamic spinal fixator systems – A finite element analysis

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