Biomechanical Analysis of Different Lumbar Interspinous Process Devices: A Finite Element Study

doi:10.1016/j.wneu.2019.04.051

World Neurosurgery

Volume 127, July 2019, Pages e1112-e1119

https://doi.org/10.1016/j.wneu.2019.04.051 Get rights and content

Background

Recently, interspinous stabilization with the interspinous process device (IPD) has become an alternative to treat lumbar spinal stenosis. The biomechanical influence of different design features of IPDs on intradiscal pressure (IDP) and facet joint force (FJF) has not been fully understood. The aim of this study was to investigate the biomechanical performance of different IPDs using finite element (FE) method.

Methods

A FE model of the L1-5 segments was developed and validated. Four surgical FE models were constructed by inserting different implants at the L3-4 segment (Coflex-F, DIAM, Wallis, and pedicle screw system). The 4 motion modes were simulated.

Results

The IPDs decreased range of motion (ROM) at the surgical level substantially in flexion and extension, but little influence was found in lateral bending and torsion. Compared with the DIAM and Wallis devices, the Coflex-F device showed advantages in stabilizing the surgical level, especially in flexion and extension, while it increased FJF at adjacent levels by 26%–27% in extension. Among the 3 IPDs, the DIAM device exhibited the most comparable ROM, IDP, and FJF at adjacent levels compared with the intact lumbar spine. The influence of the Wallis device was between that of the Coflex-F and DIAM devices.

Conclusions

Compared with rigid fixation, the IPDs demonstrated less compensation at adjacent levels in terms of ROM, IDP, and FJF, which may lower the incidence of adjacent segment degeneration in the long term.

Introduction

Rigid fixation using a metal plate or pedicle screw system has been a widely used surgical intervention for treating lumbar spinal stenosis (LSS).¹ However, rigid fixation may result in adverse changes at adjacent levels, including increased range of motion (ROM) and intradiscal pressure (IDP).² Recently, nonfusion devices such as the interspinous process device (IPD) have been developed to mitigate adjacent segment degeneration (ASD) through preserving spinal movement and improving load transmission of the lumbar spine.³ Previous studies have indicated that the IPD is an efficient alternative to rigid fixation because it provides satisfactory clinical and functional outcomes.⁴ In addition, a meta-analysis including 27 clinical studies and 2241 patients also reported that compared with rigid fusion, the IPD showed the same postoperative outcome, but may lower the incidence of ASD.⁵

A number of IPDs, such as Coflex (Paradigm Spine, Wurmlingen, Germany), DIAM (Medtronic Sofamor Danek, Paris, France), Wallis (Abbott Laboratories, Bordeaux, France), and X-Stop (Medtronic, Inc., Sunnyvale, California, USA) have been developed to treat LSS with different biomechanical designs. Some studies have investigated the biomechanics of different IPDs. Wilke et al.⁶ reported that the IPDs strongly stabilized and reduced the IDP only in extension, but had little effect in other motion modes in their in vitro study. Lo et al.⁷ in their finite element (FE) study found that Coflex-F (addition of 2 rivets to the Coflex device) can stabilize the surgical level in all motion modes, and their results were consistent with a previous in vitro study.⁸ Park et al.⁹ researched the effects of the ligature's pretension on the spinous process fracture by FE method. Some scholars also optimized the structure of IPDs by topology optimization.10, 11 However, the influence of the different biomechanical designs of IPDs on lumbar stability, IDP, and facet joint force (FJF) has not been fully understood.

Hence, the aim of this study was to investigate the biomechanics of different IPDs using FE method. Three IPDs (Coflex-F, DIAM, and Wallis) and a pedicle screw system were selected in this study. The main variables include ROM and IDP at the surgical and adjacent levels, and FJF at adjacent levels.

Section snippets

FE Modeling of the Intact Lumbar Spine and IPDs

A 3-dimensional (3D) FE model of the L1-5 segments was developed as shown in Figure 1. The geometry of the lumbosacral spine was obtained from 0.7-mm-thick computed tomography scans of a healthy adult female (age, 36 years; height, 158 cm; weight, 52 kg). The computed tomography scan images were transformed into a 3D geometric model in Mimics (Materialise Inc., Leuven, Belgium). Then the geometric model was meshed in Hypermesh (Altair Technologies, Inc., Fremont, California, USA). The final FE

Model Validation

Under 4 pure moments, the results of ROM were compared with the previous experimental results by Renner et al.,²⁰ as shown in Figure 3A. For the L4-5 IDP and axial displacement, the results were compared with those in the studies by Berkson et al.²¹ and Brinckmann et al.²² (Figures 3B and 3C). A mesh convergence test was performed based on the ROM of the intact model. The final mesh density was chosen since the difference was within 5%.

ROM

At the surgical level (L3-4), the results of the ROM were

Discussion

IPDs are designed based on the concept of restoring foraminal and disk heights and unloading the facet joints while allowing ROM to some extent.²⁵ Encouraged by its minimally invasive characteristics, IPDs have become popular as an alternative treatment for LSS, and various products are currently available in the market. However, comparative biomechanical studies among the different systems are rare. It is necessary to evaluate how different design features of the IPDs influence lumbar

Conclusions

In this study, we used a L1-5 FE model to investigate the biomechanics of different IPDs. Each implant exhibited advantages and disadvantages. Compared with rigid fixation, the IPDs demonstrated less compensation at adjacent levels in terms of ROM, IDP, and FJF, which may lower the incidence of ASD in the long term. Among the 3 IPDs, the DIAM device exhibited the most comparable ROM, IDP, and FJF at adjacent levels compared with the intact model. However, the DIAM device cannot provide

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Cement-augmentation is a technique commonly used during posterior lumbar instrumented fusion (PLIF) to reinforce compromised osteoporotic vertebral bone, minimize the risk of loosening screws, enhance stability, and improve overall surgical outcomes. In this study, we introduce a novel segmented vertebral body regional modeling approach to investigate the effects of osteoporosis and cement-augmented lumbar fusion on disc biomechanics at spinal levels adjacent to the fused vertebrae. Using our previously validated personalized-poroelastic-osteoligamentous FE model of the spine, fusion was simulated at L4-L5, and the biomechanics of adjacent levels were studied for 30 patients (non-osteoporotic patients (N = 15), osteoporotic patients (N = 15)). PLIF models, with and without cement-augmentation, were developed and compared after an 8 h-rest period (200 N), following a 16 h-cyclic compressive loading of 500–1000 N (40 and 20 min, respectively). Movement in different directions (flexion/ extension/ lateral bending/ axial rotation) was simulated using 10Nm moment before and after cyclic loading. The material mapping algorithm was validated by comparing the results of voxel-based and parametric models. The FE cement-augmented models, subject to daily activity loading, demonstrated significant differences in disc height loss and fluid loss as compared to non-cemented models. The calculated axial stress and fiber strain values were also significantly higher for these models. This work demonstrates that although osteoporosis does not significantly alter the time-dependent characteristics of adjacent IVDs post-surgery, cement-augmentation increases the risk of adjacent segment disease (ASD) incidence. A holistic understanding of the trade-offs and long-term complex interplay between structural reinforcement modalities, including cement augmentation, and altered biomechanics warrants further investigation.
Decompression Alone Versus Interspinous/Interlaminar Device Placement for Degenerative Lumbar Pathologies: Systematic Review and Meta-Analysis
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Interspinous devices (ISDs) and interlaminar devices (ILDs) are marketed as alternatives to conventional surgery for degenerative lumbar conditions; comparisons with decompression alone are limited. The present study reviews the extant literature comparing the cost and effectiveness of ISDs/ILDs with decompression alone.
Articles comparing decompression alone with ISD/ILD were identified; outcomes of interest included general and disease-specific patient-reported outcomes, perioperative complications, and total treatment costs. Outcomes were analyzed at <6 weeks, 3 months, 6 months, 1 year, 2 years, and last follow-up. Analyses were performed using random effects modeling.
Twenty-nine studies were included in the final analysis. ILD/ISD showed greater leg pain improvement at 3 months (mean difference, −1.43; 95% confidence interval, [−1.78, −1.07]; P < 0.001), 6 months (−0.89; [−1.55, −0.24]; P = 0.008), and 12 months (−0.97; [−1.25, −0.68]; P < 0.001), but not 2 years (P = 0.22) or last follow-up (P = 0.09). Back pain improvement was better after ISD/ILD only at 1 year (−0.87; [−1.62, −0.13]; P = 0.02). Short-Form 36 physical component scores or Zurich Claudication Questionnaire (ZCQ) symptom severity scores did not differ between the groups. ZCQ physical function scores improved more after decompression alone at 6 months (0.35; [0.07, 0.63]; P = 0.01) and 12 months (0.23; [0.00, 0.46]; P = 0.05). Oswestry Disability Index and EuroQoL 5 dimensions scores favored ILD/ISD at all time points except 6 months (P = 0.07). Reoperations (odds ratio, 1.75; [1.23, 2.48]; P = 0.002) and total care costs (standardized mean difference, 1.19; [0.62, 1.77]; P < 0.001) were higher in the ILD/ISD group; complications did not differ significantly between the groups (P = 0.41).
Patient-reported outcomes are similar after decompression alone and ILD/ISD; the observed differences do not reach accepted minimum clinically important difference thresholds. ISD/ILDs have higher associated costs and reoperation rates, suggesting current evidence does not support ILD/ISDs as a cost-effective alternative to decompression alone.
Biomechanical analysis of a customized lumbar interspinous spacer based on transfacetopedicular screw fixation: A finite element study
2022, Medical Engineering and Physics
The interspinous spacer (ISP) is a minimally invasive surgical device implanted into the interspinal space to treat lumbar degenerative diseases. Unfortunately, ISPs sometimes cause device breakage and spinal process fracture. Our aim was to elaborate the design of lumbar customized posterior fixation system (CISP system), encompassing a customized ISP body and transfacetopedicular screws, and examine its biomechanical effect on the lumbar spine using finite element (FE) analysis. We constructed the CISP system, based on the interspinal anatomical data at the surgical level. We generated the L3-S1 FE models, implanted with the polyetheretherketone (PEEK) CISP system, titanium alloy (TI) CISP system, and Coflex device at the L4/L5 segment, and determined the lumbar segmental range of motions (ROMs), intervertebral discs (IVD) peak stress, and implant stresses. The CISP system enhanced mobility restriction at the surgical level, compared to the Coflex device. Furthermore, the IVD peak stress reduction was more obvious in the CISP system than the Coflex device, particularly during extension. Under the same motion mode, the maximum stress on the TI CISP system was smaller than on the Coflex device, but larger than the PEEK CISP system. Given these evidences, PEEK appeared to be a better material for the CISP body.
Comparative biomechanical analysis of rigid vs. flexible fixation devices for the lumbar spine: A geometrically patient-specific poroelastic finite element study
2021, Computer Methods and Programs in Biomedicine
Citation Excerpt :
Combined with topology optimization methods, FE modeling has been successfully used to evaluate the performance of novel ISP devices [21]. Such studies yielded significant results, particularly for comparative analyses, where biomechanical evaluation of different ISPs demonstrated that flexible devices result in less functional compensation of motion at adjacent spinal levels [22]. On the other hand, most existing FE studies for the biomechanical assessment of healthy, diseased, and treated spines are constrained to unique geometries.
Lumbar spinal stenosis (LSS), or the narrowing of the spinal canal, continues to be the leading preoperative diagnosis for adults older than 65 years who undergo spine surgery. Although the treatment of LSS depends on its severity, the optimal surgical technique towards decreasing the risk of adjacent segment disease (ASD) remains elusive. This study aimed to comparatively analyze spinal biomechanics with rigid and flexible fixation devices (i.e., rigid and dynamic posterolateral fusion (PLF) and interspinous process (ISP) devices) during daily activities.
Using a validated parametric poroelastic finite element modeling approach, 8 subject-specific pre-operative models were developed, and their validity was evaluated. Parametric FE models of the lumbar spines were then regenerated based on post-operation images for (A) rigid PLF (B) dynamic PLF (C) rigid ISP device (Coflex) and (D) flexible ISP device (DIAM) at L4-L5 level. Biomechanical responses for instrumented and adjacent intervertebral discs (IVDs) were analyzed and compared subject to static and cyclic loading.
The preoperative models were well comparable with previous works in literature. The postoperative results for the PLF and Coflex rigid systems, demonstrated greater ROM; higher values of stress and strain in the AF region; and increased disc height and fluid loss at the adjacent levels, as compared with the pre-op models and the post-op results of the flexible systems (i.e., dynamic PLF and DIAM). The calculated forces on the facet joint were of smaller magnitude for the ISP devices as compared to the PLF, particularly during extension.
This study demonstrates that the dynamic PLF construct and DIAM implants could be effective to maintain the natural poroelastic characteristics of adjacent IVDs, which could be beneficial for enhancing long-term clinical outcomes. FEM provides clinicians with an invaluable patient-specific quantitative tool for informed surgical planning and discerning follow-up management.
Posterior Lumbar Interbody Fusion Versus Transforaminal Lumbar Interbody Fusion: Finite Element Analysis of the Vibration Characteristics of Fused Lumbar Spine
2021, World Neurosurgery
Citation Excerpt :
An in vitro biomechanical study by Sim et al.17 reported that PLIF provided a higher immediate stability than TLIF in flexion, extension, lateral bending, and axial rotation. The finite element (FE) method provides an easy way to investigate the mechanical stress and deformation in the spinal components.18-20 For example, some FE studies found that under the bending moments in all directions, compared with PLIF, TLIF decreased intradiscal pressure and intersegmental rotation at adjacent motion segments than PLIF,21 but slightly increased the posterior screw stress.22
Previous studies have investigated biomechanical characteristics of the lumbar spine after different types of lumbar interbody fusion surgery under static loadings. However, very few have dealt with the whole-body vibration (WBV) condition that is typically present in vehicles. The aim of this study was to compare the influence of posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF) on dynamic responses of the fused lumbar spine to vertical WBV.
The PLIF and TLIF procedures with bilateral pedicle screw fixation at L4-L5 level were simulated by modifying a previously validated intact lumbar L1-S1 finite element model. The PLIF and TLIF models were subjected to a sinusoidal vertical load with a compressive follower preload, and computed for transient dynamic analysis. The obtained dynamic responses for the models at the fused and adjacent levels were collected and compared.
The results showed that the contact force between endplate and cage was higher in the PLIF model than in the TLIF model, indicating that PLIF allowed for higher compressive load across the anterior structure. At fused L4-L5 level, the TLIF led to a higher stress in the endplate and posterior BPSF system than the PLIF. At adjacent L3-L4 level and L5-S1 level, the computed dynamic responses, in terms of stress and deformation, for the PLIF and TLIF models showed very few differences.
This study may be helpful to quantify dynamic mechanical properties of the fused lumbar spine, and better understand biomechanical differences between the PLIF and TLIF procedures during vibration.
Biomechanical evaluation of anterior lumbar interbody fusion with various fixation options: Finite element analysis of static and vibration conditions
2021, Clinical Biomechanics
Citation Excerpt :
The model included cortical bone, cancellous bone, posterior elements, intervertebral discs, and 7 types of ligaments. Detailed modeling procedures and validation results were described elsewhere (Shen et al., 2019). To simulate the ALIF procedure, with the patient in the supine position, the L3–4 segment of the lumbar spine underwent partial discectomy and total nuclectomy by the anterior approach, which included removal of the anterior longitudinal ligaments, entire nucleus pulposus, and partial annulus (Fan and Guo, 2019).
Anterior lumbar interbody fusion combined with supplementary fixation has been widely used to treat lumbar diseases. However, few studies have investigated the influence of fixation options on facet joint force and cage subsidence. The aim of this study was to explore the biomechanical performance of anterior lumbar interbody fusion with various fixation options under both static and vertical vibration loading conditions.
A previously validated finite element model of the intact L1–5 lumbar spine was employed to compare five conditions: (1) Intact; (2) Fusion alone; (3) Fusion combined with anterior lumbar plate; (4) Fusion combined with Coflex-F fixation; (5) Fusion combined with bilateral pedicle screw fixation. The models were analyzed under static and vertical vibration loading conditions respectively.
Bilateral pedicle screws provided highest stability at surgical level. Applying supplementary fixation diminished the dynamic responses of lumbar spine. Compared with anterior lumbar plate and Coflex-F device, bilateral pedicle screws decreased the stress responses of the endplates and cage under both static and vibration conditions, while increased the facet joint force at adjacent levels. As for comparison between Coflex-F device and anterior lumbar plate, results showed a similarity in biomechanical performance under static loading, and a slightly higher dynamic response of the latter under vertical vibration.
The biomechanical performance of lumbar spine was significantly influenced by the variation of fixations under both static and vibration conditions. Bilateral pedicle screws showed advantages in stabilizing surgical segment and relieving cage subsidence, but may increase the facet joint force at adjacent levels.

View all citing articles on Scopus

: Conflict of interest statement: This study was supported by the National Key Research and Development Plan (2016YFC1102002) and the Application Demonstration Project of Shenzhen (KJYY20170405161248988).

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Original ArticleBiomechanical Analysis of Different Lumbar Interspinous Process Devices: A Finite Element Study

Background

Methods

Results

Conclusions

Introduction

Section snippets

FE Modeling of the Intact Lumbar Spine and IPDs

Model Validation

ROM

Discussion

Conclusions

Clin Neurol Neurosurg

Clin Biomech

Comput Biol Med

Med Eng Phys

BMC Musculoskelet Disord

J Biomech

Clin Biomech

Kinematic evaluation of lumbar fusion techniques

Spine

Adjacent segment degeneration and adjacent segment disease: the consequences of spinal fusion?

Spine J

Dynamic interspinous process technology

Spine

Interspinous implants (X Stop (R), Wallis (R), Diam (R)) for the treatment of LSS: is there a correlation between radiological parameters and clinical outcome?

Eur Spine J

Biomechanical effect of different lumbar interspinous implants on flexibility and intradiscal pressure

Eur Spine J

Biomechanical effect after Coflex and Coflex rivet implantation for segmental instability at surgical and adjacent segments: a finite element analysis

Comput Methods Biomech Biomed Eng

Pre-tension effects from tightening the ligature on spinous process fracture risk in interspinous process device implantation

Int J Precision Eng Manufacturing

Biomechanical analysis of a new lumbar interspinous device with optimized topology

Med Biol Eng Comput

Finite element analysis and design of an interspinous device using topology optimization

Med Biol Eng Comput

Original Article
Biomechanical Analysis of Different Lumbar Interspinous Process Devices: A Finite Element Study